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SPECIES COMPOSITION AND INFECTION RATES OF MOSQUITOES AND SAND
FLIES IN MRIMA HILL, KWALE COUNTY, KENYA
ONYIEGO JUDITH ADHIAMBO, B. Ed. (Sc.)
REG NO.: I56/CE/14164/2009
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE AWARD OF THE DEGREE OF MASTER OF SCIENCE
(APPLIED MEDICAL PARASITOLOGY) IN THE SCHOOL OF PURE AND
APPLIED SCIENCES OF KENYATTA UNIVERSITY
MAY 2016
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DECLARATION
This thesis is my original work and has not been presented for a degree in any other
University or for any other award.
Onyiego Judith Adhiambo
Department of Zoological Sciences
Signature: ……………………………….. Date …………………
SUPERVISORS:
This thesis has been submitted with our approval as supervisors
Professor Jones Mueke
Department of Zoological Sciences
Kenyatta University
Signature: ……………………………….. Date…………………….
Dr. Christopher O. Anjili
Centre for Biotechnology Research and Development
Kenya Medical Research Institute (KEMRI)
Signature: ………………….……………… Date…………………
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DEDICATION
This thesis is dedicated to my beloved husband Phineas and children Brent, Euan and
little Mary Dora. My parents: The late Mr and Mrs Onyiego in their memory for inspiring
me. My siblings: Beaty, Izo, Liz, Anuar and Lavenda.
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ACKNOWLEDGMENT
My uttermost gratitude goes to the Almighty God for his wholesome support, special and
sincere thanks to my supervisors, Professor Jones Mueke, for constantly keeping me on
toes when I was lazing and lagging behind schedule and his constant encouragement. I
sincerely appreciate Dr Chris Anjili‘s guidance, total devotion and mentoring. Together
and individually they inspired me by their commitment towards this work. I appreciate
the input of the Department of Zoological Sciences for the intellectual support especially
from Dr Joshua Mutiso. I am also indebted to Mr. Kevin Kimenyi for the assistance he
offered me during my trips to Mrima hill. My heartfelt gratitude goes to the villagers of
Mrima hill, headed by the chairman Mr. Omar Bakari and his nephew Mr. Ahmadi
Bakari for being my helper during my work in the village and to my institutional head
Mr. Godfrey Njoroge for all the ample time I needed during the whole process. I finally
acknowledge the special part played by my family; my husband for all round support, my
dear sons Brent Jamba and Euan Tiany for their admiration that inspired me to move on
even when things felt hard, my little girl Mary Dora for the sacrifice of time that mum
spent away. My sister, Mrs. Elizabeth Obura and her family for financial support and the
rest of Konyiego people for their love. Ms Everlyn Samita Khakai, my best friend, for the
greatest contribution; constant prodding, objective criticism and positive reinforcements
throughout this work. To all, I say thank you.
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TABLE OF CONTENTS
Declaration .......................................................................................................................... ii
Dedication .......................................................................................................................... iii
Acknowledgment ............................................................................................................... iv
Table of content…………………………………………………………………………...v
List of tables ..................................................................................................................... viii
List of figure……………………………………………………………………………...ix
List of plates ........................................................................................................................ x
Abbreviation and Acronyms ............................................................................................. xi
Abstract………………………………………………………………………………….xiii
CHAPTER ONE: INTRODUCTION ............................................................................. 1
1.1 Background information ............................................................................................... 1
1.2 Statement of the problem .............................................................................................. 4
1.3 Justification of study ..................................................................................................... 5
1.4 Research questions ........................................................................................................ 6
1.5 Hypotheses .................................................................................................................. 6
1.6 Objectives of the study.................................................................................................. 6
1.6.1 General objective ....................................................................................................... 6
1.6.2 Specific objectives………………………………………………………………......7
1.7 Significance of the study............................................................................................... 7
CHAPTER TWO: LITERATURE REVIEW ................................................................ 8
2.1 Mrima Hill .................................................................................................................... 8
2.1.1 Historical background ................................................................................................ 8
2.1.2 The Flora and Fauna of Mrima Hill ......................................................................... 11
2.1.2.1 The Flora ............................................................................................................... 11
2.1.2.2 The Fauna.............................................................................................................. 13
2.2 Natural radiation ........................................................................................................ 15
2.2.1 Thorium.................................................................................................................... 17
2.2.1.1 Physical properties of Thorium ............................................................................. 17
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2.2.1.2 Radioactivity ......................................................................................................... 17
2.2.1.3 Effects on humans ................................................................................................ 18
2.2.2 Effects of radiation on living organisms .................................................................. 19
2.2.2.1 Polytene chromosomes and genes ........................................................................ 19
2.2.2.2 The cytogenetic effects of thorium radiation on organisms.................................. 20
2.2.2.3 Insect sterilization by radiation…………………………………………………..22
2.2.2.4 Sterile insect technique ......................................................................................... 23
2.3 Species composition of mosquitoes and sand flies ..................................................... 24
2.3.1 Mosquitoes species and their infections .................................................................. 24
2.3.2 Sand flies species and their infections ..................................................................... 28
2.4 Vector-borne parasitic diseases in Kwale County ...................................................... 29
2.4.1 Prevalence of Malaria .............................................................................................. 29
2.4.2 Prevalence of Filariasis ............................................................................................ 29
2.4.3 Prevalence of Leishmaniasis .................................................................................... 31
2.5 Present study ............................................................................................................... 31
CHAPTER THREE: MATERIALS AND METHODS .............................................. 32
3.1 Study area.................................................................................................................... 32
3.1.1 Location of Mrima Hill ............................................................................................ 32
3.2 Pilot study ................................................................................................................... 36
3.3 Sampling procedure……………………………………………………………….....36
3.4 Laboratory procedures ................................................................................................ 38
3.4.1 Specimen preparation and staining with Giemsa stain ............................................ 38
3.4.2 Preparation of chloral hydrate mounting gum……………………………………..39
3.4.3 Procedure for mounting specimen using chloral hydrate mounting gum ................ 39
3.5 Species identification using anatomical features ........................................................ 40
3.5.1 Mosquitoes ............................................................................................................... 40
3.5.2 Sand flies.................................................................................................................. 40
3.6 Examination for parasites ........................................................................................... 40
3.7 Data Analysis .............................................................................................................. 41
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CHAPTER FOUR: RESULTS ...................................................................................... 42
4.1 Composition of trapped mosquitoes and sand flies .................................................... 42
4.1.1 Mosquitoes………………………………………………………………………....42
4.1.2 Sand flies.................................................................................................................. 44
4.2 Relationship between number of mosquitoes and sand flies………………………...46
4.3 Relationship between levels of radiation and number of mosquitoes and sand flies...46
4.3.1 Relationship between levels of radiation and number of mosquitoes……………...46
4.3.2 Relationship between levels of radiation and number of sand flies………………..47
4.4 Relationship between Radiation and Elevation .......................................................... 48
4.5 Vector infection rates .................................................................................................. 49
CHAPTER FIVE: DISCUSSION.................................................................................. 50
5.1 Trapped mosquitoes and sand flies ............................................................................. 50
5.1.1 Mosquito species ...................................................................................................... 50
5.1.2 Sand fly species........................................................................................................ 54
5.2 Infection rates.............................................................................................................. 56
5.3 Relationship between radiation and elevation ............................................................ 56
CHAPTER SIX: CONCLUSION AND RECOMMENDATIONS……………….....57
6.1 Conclusions ................................................................................................................. 57
6.2 Recommendations ....................................................................................................... 58
REFERENCES ................................................................................................................ 59
APPENDICES…………………………………………………………………………..69
APPENDIX I…………………………………………………………………………….69
APPENDIX II……………………………………………………………………………70
APPENDIX III…………………………………………………………………………...71
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LIST OF TABLES
Table 4.1: Number of mosquitoes species collected, their percentage, elevation (m (ASL)
and radiation level (mSv/yr) around the Mrima study area………………….43
Table 4.2: Number of sand fly species collected, their percentage, elevation (m (ASL)
and radiation levels (mSv/yr) around the Mrima study area……………...…..45
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LIST OF FIGURES
Figure 3.1 Map of mrima hill area where the study was carried out in Kwale County ...36
Figure 4.1 Relationship between number of mosquitoes and sand flies………………...46
Figure 4.2 Relationship between levels of Radiation and number of mosquitoes...…….47
Figure 4.3 Relationship between levels of Radiation and number of sand flies......…….48
Figure 4.4 Relationship between levels of Radiation and levels of Elevation...………...49
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LIST OF PLATES
Plate 2.1: Agricultural land on the North west of Mrima Hil ………..………………..10
Plate 2.2: A typical homestead on the South East of the Mrima Hill ...………………..11
Plate 2.3: Rhynchocyon petersi ……………………………...………………………...14
Plate 2.4: Galago zanzibaricus ……………………………...………………………....14
Plate 2.5: Colobus angolensis palliates …………...…………………………………...15
Plate 2.6: Myonycteris relicta the fruit bat …..………………………………………...15
Plate 2.7: Features found on the head of Myonycteris relicta fruit bat ……...…………15
Plate 3.1: Images of Mrima Hill …………………………………………..……………35
Plate 3.2: A light trap set in the upper part of the hill to trap mosquitoes and sandflies 37
Plate 3.3: A light trap suspended outside a house to trap mosquitoes and sandflies ...…38
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ABBREVIATION AND ACRONYMS
ARS
Acute radiation syndrome
ASL
Above sea level
CEPF
Critical Ecosystem Partnership Fund
CHIKV
Chikungunya
CPMs
Counters per Minute
CRC
Computing Research Centres
DNA
Deoxyribonucleic acid
DOD
Department of Defence
EARPO
East Africa Regional Programme Office
ELISA
Enzyme-linked immunosorbent Assay
GPS
Geographical Positioning Systems
HBRAs
High background radiation areas
ICPR
International Commission for Radiological Protection
IUCN
International Union for Conservation of Nature
IUPAC
International Union of Pure and Applied Chemistry
KEMRI
Kenya Medical Research Institute
MASL
Metres Above the Sea Level
Mrems
millirem
mSv/yr
milliSieverts per year
Nb
Niobium
NEMA
National Environmental Management Authority
NNDC
National Nuclear Data Center
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Pb
Lead
PBS
Phosphate-buffered saline
PCR
Polymerase Chain Reaction
PH
Power of Hydrogen
PPM
Parts per Million
Rem
Roentgen equivalent man
Sr
Strontium
SAM
Solid State Army
SI
Standard unit
SNAP
System for Nuclear Auxillary Power
SPSS
Statistical Package for the Social Sciences
SV
Sievert
SIT
Sterile insect technique
Th
Thorium
UEPA
United States Environmental Protection Agency
UNSCEAR
United Nation Science Committee on Environmental Atomic Radiation
WHO
World Health Organization
WNV
Western Nile Virus
WWF
World Wide Forests
2
Chi-square test
Yt
Yittrium
Zn
Zinc
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ABSTRACT
Mrima hill in Kwale County, along the Kenyan coast, is known to have high natural
background radiation caused mainly by 232 Thorium (Th). Currently, the area also has no
proper sanitary disposal system and people use bushes as toilets. There are no fresh water
bodies. Despite other parts of the coastal regions of Kenya having been studied for
human disease vectors including mosquitoes and sandflies, no studies have been carried
out in Mrima hill to establish the prevalence of these important vectors. The main aim of
the present study was to determine mosquitoes and sand flies species diversity as well as
vector infection rates in order to establish the level of risk of infection with malaria and
leishmaniasis for the local inhabitants. The relationship between radiation and population
sizes of both mosquitoes and sand flies was determined. This study also established the
relationship between levels of radiation and elevation. Thirty eight houses were randomly
selected and radiation levels taken using hand held Digilert 100 CPMS reader and
recorded. Mosquitoes and sand flies were caught using light traps and counted to
establish their population. Species identification was done on mosquitoes and sand flies
using standard taxonomic keys. All captured female insects were dissected and examined
for presence of parasites to establish the infection rates. Data were analyzed using the
Statistical Package for Social sciences (SPSS) Version 20 (2011) utilizing Chi-square and
Pearson correlation. A total of 131 mosquitoes and 39 sand flies were captured. Apart
from the Aedes aegypti species (1.9%), the only other species of medical importance that
were collected in the study area included: Culex pipiens (69.42%), Cx vansomernae
(1.5%), Mansonia africana (18.32%) and M. uniformis (9.6%). None of these mosquitoes
are known vectors of disease in Kenya. Phlebotomine sand fly species that were collected
included Sergentomyia bedfordi (74.36%), S. suberecta (15.35%), S. meilloni (5.12%) S.
schwetzi (2.56%) and S. inermis (2.56%). None of these species has been indicated to be
of any medical importance in Kenya. The highest radiation level recorded was 17.5
milliSieverts/year whereas the lowest was 5.9 mSv/year; with a mean radiation of 10.52
mSv/year. There was no significant relationship between radiation levels and number of
mosquitoes (2 = 103.7; df = 99; P = 0.353) or sandflies (2 = 40.0; df = 55; P = 0.936)
collected. There was no significant relationship between the number of mosquitoes and
sand flies (2 =36 and P=0.165). In addition, there was no correlation between radiation
levels and elevation (r = -0.389; df= 10; P=0.211). From the results of this study it can be
concluded that it is unlikely that the insect- borne diseases can occur in Mrima hill, unless
the disease causing pathogens are introduced. There is need for further studies to
establish the effect of radiation on reproductive capacity and survival of disease vectors
in the present study area.
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CHAPTER ONE: INTRODUCTION
1.1 Background information
Species composition of mosquitoes and sand flies have been researched and established
in different parts of the world. There are several species of mosquitoes that are vectors of
different tropical diseases. Studies have shown that there is low density of vectors across
sub-Saharan Africa. A study carried out in Mwea Kenya sampled about twenty one
species of mosquitoes where genera Culex, Anopheles, Mansoni, Ficalbia and Aedes
constituted the majority of the catches. In the study Culex quiquefasciatus Say was the
most abundant species caught (Muturi et al., 2007).
There are more than 4000 mosquito species in the world today but only a tenth of these
are efficient vectors of diseases that have impact on the welfare and health of humans
(Manguin et al., 2009). Malaria and lymphatic filariasis have been ranked as the two
most identifiable mosquito-borne parasitic diseases worldwide. These two infections are
transmitted by the same vector species of mosquitoes. Anopheles gambiae and A. funestus
s.l Giles have been classified as the most important vectors of malaria and lymphatic
filariasis. The two species occur all year round in their habitats with peaks of their
population abundance coinciding with seasonal rains (Onyango et al., 2013). Culex
quinquefasciatus is also known to transmit lymphatic filariasis. Mosquitoes also transmit
West Nile Virus through their bites. They acquire the virus from birds which are usually
the reservoir (Hayes et al., 2005). West Nile Virus is primarily transmitted by Culex
mosquitoes but can also be transmitted by mosquitoes from other genera. In Europe and
Africa, the principal vectors are Culex pipiens, Cx. univittatus and Cx. antennatus while
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in India, it is Cx. vishnui (Hayes et al., 2005). Mosquitoes are known vectors of
Chikungunya which was first reported in Tanzania in 1952. Chikungunya is a zoonotic
arthropod-borne virus endemic mostly in Africa, India and South East Asia spread and
transmitted by mosquito species of Aedes albopictus. In Africa, the virus is maintained in
circulation with sylvatic cycle with wild mosquitoes; Aedes furcifer, Ae. luteocephalus,
Ae. taylori, Ae. africanus with preferred feeding on primates (Vazeille et al., 2007).
Chikingunya virus is mainly transmitted within urban cycles in an inter-human
transmission in Asia. The transmission is done by the human biting Ae. aegypti which
breeds in man-made sites and the less anthrophilic, Ae. albopictus, also known as the
Asian tiger mosquito (the native of South East Asia) (Vazeille et al., 2007). Mosquitoes
transmit yellow fever which is the original viral hemorrhagic fever which was feared as
the most dangerous disease before the development of an effective vaccine. The disease
still affects as many as 200,000 persons annually in tropical regions of Africa and South
America. It also poses a significant hazard for unvaccinated travelers. The yellow fever is
transmitted by a cycle involving monkeys and mosquitoes but humans can also act as
viraemia host for mosquito infection (Monath, 2001). Dengue and Dengue hemorrhagic
fever are caused by four serotype viruses of the genus Flavivirus. Dengue fever is
majorly an urban disease of the tropics. This virus is caused and maintained in a cycle
that involves humans and day-biting mosquito Aedes aegypt, that prefer feeding on
human (Gubler and Clark, 1995).
Sand flies are also known to be of many species some of which are serious vectors of
deadly parasitic diseases. They transmit infections that affect humans and various animal
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populations throughout much of the tropics and subtropics. The infected female
phlebotomine sand flies spread the infection through their bites. Phlebotomine sand flies
are dipteran insects of the family psychodidae and approximately 700 species have been
described in different places. The female sand flies (Phlebotomine species in the Old
world and Lutzomyia species in the new world) acquire Leishmania parasites when they
feed on infected mammalian host in search of the bloodmeal (Bates, 2007). The parasites
produce a spectrum of diseases in their human hosts including cutaneous and visceral
forms which always depend on the species of sand flies that are transmitting these
parasites (Sacks, 2001). Sergentomyia sand fly species usually feed on reptiles as well as
other vertebrates thereby transmitting Leishmania parasites which are also commonly
referred to as Sauro leishmania (Bates, 2007).
Although studies on species composition and infection rates have been done elsewhere in
the world, no research has been conducted in areas with high natural background
radiation. High natural background radiation level in Mrima hill has been reported and is
attributed to presence of weathered carbonatite rock with high Thorium concentration
(Patel, 1991; Malathi, 2005). High natural background radiation has also been reported in
some other areas in Kenya including: Ruri, Kuge, Sokolo and Rangwa on the shores of
Lake Victoria. This is associated with carbonate rock containing high concentration of
thorium and uranium (Achola et al., 2012).
Mrima hill in Kwale County has been reported to have elevated radiation (Patel, 1991).
Apart from the total solar radiation (TSI), the area has high radiation believed to have
4
been caused by among other elements;
232
Thorium (Th), which is also the main element
releasing radiation into the environment (Patel, 1991). Radioactivity studies have shown
that the upper and lower parts of Mrima hill have an annual radiation of 10,670 mrems
[106.7 milliSieverts (mSv)] and 1,372 mrems [13.72 milliSieverts (mSv)], respectively.
These doses are approximately 53 times higher than the natural background dose of 240
mrems (2.4 mSv per year), what the Commission on International Radiological
Protection considers normal (UNSCEAR, 1988). The upper and middle parts of the hill
have 106.7 milliSievert yet the annual limit of effective dose is equivalent to 50
milliSieverts (Patel, 1991). The aim of the present study was to establish the composition
of species and infection rates of mosquitoes and sand flies in Mrima hill in Kwale
County.
1.2 Statement of the problem
It has been suggested that Mrima forest conservation zone, particularly Mrima hill has
elevated radiation levels (Patel, 1991). There is limited information available on species
composition of any vectors of disease in such areas with High Natural Background
Radiation. However, there is data on the use of radiation in the laboratory to sterilize
insects such as male tsetse flies (the sterile male technique), as a control measure for their
population and the disease (Dyck et al., 2005). Data on the endemicity of the human
vector-borne parasitic diseases in the Mrima hill and its environs is inadequate even
though Kwale County is known to be endemic for diseases such as malaria, filariasis and
trypanosomiasis (Wanyiri, 1996; Mwandawiro et al., 1997; Mbogo et al., 2000). As early
as 1964, it was reported that phlebotomine sand flies (Diptera: Psychodidae) are present
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in Kwale (Minter, 1964). Since then, no follow up studies have been carried out to
establish the variety of species which are capable of transmitting human leishmaniases in
this area. Transmission of vector borne diseases is known to be prevalent in Kwale, but
the species of vectors at Mrima hill have not been determined. It is for this reason that
studies were undertaken to establish the species composition of mosquitoes and sand fly
vectors of human diseases in this area. This study also aimed at investigating the levels of
radiation in the area of study and parasite infection levels in the vectors.
1.3 Justification of study
Arthropod-borne infections have emerged as a major human health concern worldwide.
Those spread by mosquitoes have caused most serious and wide spread parasitic diseases
and arbovirus diseases worldwide and are ubiquitous in both feral and urban settings
(Ottesen, 2000). The viruses include; Dengue, yellow fever, rift valley fever and
chikungunya among others. Malaria and Lymphatic filariasis are among the world‘s most
dreaded killer diseases claiming several million lives yearly and disabling and disfiguring
more and hence the need to establish their vector status in Mrima Hill. Leishmaniasis,
transmitted by infected female phlebotomine sand flies, is also one of the most important
vector-borne diseases reported world-wide with estimated half a million new cases and
around 50 thousand deaths per year (Bates, 2007). These facts led to the study of the
species composition and infection rates of mosquitoes and sand flies in the area of Mrima
hill to be able to establish their role in disease transmission in high natural background
radiation area owing to the fact that the neighbouring areas have been studied.
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1.4 Research questions
i) What is the species composition of mosquitoes in the study area of Mrima hill,
Kwale County?
i) What is the species composition of sand flies in the study area of Mrima hill,
Kwale County?
ii) What is the infection rate of mosquitoes in the study area of Mrima hill, Kwale
County?
iii) What is the infection rate of sand flies in the study area of Mrima hill, Kwale
County?
iv) What is the relationship between radiation and elevation in Mrima hill, Kwale
County?
1.5 Hypotheses
i) There are no mosquito species that are vectors of diseases in Mrima hill.
ii) There are no sand fly species that are vectors of diseases in Mrima hill.
iii) There are no infections transmitted by mosquitoes in Mrima hill.
iv) There are no infections transmitted by sandflies in Mrima hill.
v) There is no relationship between radiation and elevation around Mrima hill.
1.6 Objectives of the study
1.6.1 General objective
To establish the species composition and infection rates of mosquitoes and sand flies in
Mrima hill, Kwale County in Kenya.
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1.6.2 Specific objectives
i) To determine the species composition of mosquitoes in Mrima hill, Kwale
County.
ii) To determine the species composition of sand flies in Mrima hill, Kwale County.
iii) To evaluate the infection rate of mosquitoes in Mrima hill, Kwale County
iv) To evaluate the infection rate of sand flies in Mrima hill, Kwale County.
v) To determine the relationship between radiation and elevation around a high
natural background radiation of Mrima hill, Kwale County.
1.7 Significance of the study
Results obtained from the study will provide information on the species composition of
mosquitoes and sand flies in the study area and the parasitic infections transmitted by
these disease vectors (mosquitoes and sand flies). The information could be used by the
Ministry of Public Health and Sanitation to put in place the relevant control measures
against vector borne diseases in the area.
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CHAPTER TWO: LITERATURE REVIEW
2.1 Mrima Hill
2.1.1 Historical background
The Mrima hill is a small hill rising within the forest on an alkaline igneous complex that
is reported to have significant deposit ores containing manganese and niobium.
Considerable mining activities have been undertaken in the area measuring about 390
hectares (Kenya Forest Department, 1994). Mrima hill is biologically important and
significant as a kaya. The kayas are relict patches of forest that once sheltered the
fortified villages of the Mijikenda people (in Mrima‘s case, the Digo) on the Kenyan
coast. The Mrima Forest Reserve was gazetted in 1961 (NEMA, 2001). A survey in 1986
brought the kaya to the attention of the Government as a valuable cultural and natural
heritage leading to its gazettement as Mrima Sacred Grove National Monument under the
antiquites and Monuments Acts in 1992 (Githitho, 2004). The Kayas have spiritual and
ceremonial significance and are customarily protected and managed by a council of
elders. National Museums of Kenya manages the National monuments for their historical
importance. The site was made a strict nature reserve under the Forests Act in the early
1980s (Githitho, 2004).
As a forest reserve, it is managed by the Forest Department but the level of protection is
weak, given very insufficient capacity to patrol and ensure protection (Africa News
Service, 2010). Mrima hill area was one of the earliest Swahili settlements in Africa.
People who lived there depended on the forest for herbs and source of water. The main
land use in the area is forestry, nature conservation and research. Survey of Sacred Kaya
9
Forest highlighting the conservation importance for trees led to a comprehensive survey
of Kenya Coastal Forest commissioned by World-Wide Forest (Roberson and Luke,
1993). It mainly paid close attention to the plant species and status of the forest. The
survey also made recommendation for their conservation (WWF-EARPO, 2002).
The forest provides a source of building wood and fuel which include, firewood and
charcoal, making the main source of the rural household energy consumption and also the
urban energy consumption to growing towns like Mombasa and Lunga lunga (Burgess
and Muir, 1994). According to Burgess and Muir (1994), the forest was used for timber
production and main local uses such as pole collection and sawing; religious (spiritual)
and ceremonial, gathering of medicinal plants; clearing of the forest to grow crops
(agriculture); collection of edible plants and honey and mining and building hotels for
tourism. Kayas have been seriously encroached by mining for lead and other minerals
(Clark and Burgess, 2000). The forest has suffered selective logging and pole cutting.
Cutting of trees and destruction of vegetation around the Kaya was prohibited while the
surrounding areas slowly turned into farmland, leaving the Kaya site as forested patches
of varying size. Restriction by the Government due to overexploitation means much
material is harvested illegally from the Forest Reserves and other areas (Kenya Forest
Department, 1994; Githitho, 2004). Population density around the hill has increased with
encroachment on the lower slopes of the hill to the west. Mining and other activities have
also increased due to population increase. There are medium-sized forests occurring in
Kwale which have been gazetted as forest reserves for many decades yet have no
significant management presence due to the difficulty of looking after the small scattered
10
forests. These sites include, Mrima and Dzombo, a nearby hill (Kenya Forest
Department, 1994).
Subsistence farming is practised around the forest. Many people in this area are
smallholder farmers with most of them owning between 5 and 10 acres of land. However,
these farms are becoming smaller and smaller as they are sub-divided and passed onto the
male children (NEMA, 2001). Only a few farmers keep large numbers of cattle due to
lack of grazing area and lack of water supplies (especially during the dry season). Goats
and poultry, however, are found in almost every household. There are no rivers in the
area such that all the residents only use water from bore-holes. The bore-holes draw
water from rainfall permeating the soil and provide most of the groundwater resources in
Kenya (Nyaoro, 1999). A typical agricultural land is shown in Plate 2.1.
Plate 2.1: Agricultural land on the North West of Mrima Hill (Adapted from NEMA,
2001).
11
Most of the households have houses that are made of mud and are thatched with coconut
plant leaves commonly known in Kiswahili as ‗Makuti‘ (Njenga, 2007). They have no
ceilings and usually have many openings (Plate 2.2).
Plate 2.2: A typical homestead on the South East of the Mrima hill (Adopted from
Njenga, 2007).
2.1.2 The Flora and Fauna of Mrima hill
2.1.2.1 The Flora
The vegetation in Mrima hill is diversified. A record from a group of scientists on an
expedition in 1989 listed about 270 taxa, with about 25 taxa which are rare globally and
within Kenya (BirdLife International, 2012). So many known rare species of trees are
12
found on Mrima hill. These include: Uvariodendron gorgonis and Gigasiphon
macrosiphon. It was found that there were only three mature trees. At the 6th East Africa
plant Red Listing Authority meeting in April 2012 at the International Union for
Conservation of nature Headquarters in Nairobi, there was a report on the existence of the
trees in Muhaka, Gongoni and Mrima hill forest. Forests are reducing in size and
becoming areas of land used for farming and other uses such as creating villages,
constructing tourism facilities and for expanding town and cities. This has caused a
reduction in the forest cover, loss of biodiversity in the flora and fauna, reduction of
availability of water, soil erosion and loss of land productivity which negatively influence
the livelihood of the communities around. The declining forests also affect the
biodiversity of conservation and national and global benefits in terms of goods and
services (IUCN, 2014).
Most of the threatened woody plants species in Kenya occur in coastal forests.
Nationally, the threatened species of Kenya‘s coastal forests is made up of plants which
make half of the total plant cover and more than half are birds and mammals (Njenga,
2007). The forests are ranked 11th in species endemism by Conservation International and
BirdLife International ranks it as one of the most globally important endemic Bird area
(Bennun and Njoroge, 1996). According to Clark and Burgess (2000) and CEPF (2003),
the area is considered to be a major global conservation priority due to threat of
endemism. The Mrima hill forest has farm holdings around it with farms growing maize
and there are also rice paddies. Fruits grown in the area include: pawpaw, mangoes,
oranges, tangerine, lime, melons, coconut and cashew nut among others. Although many
13
uses of the forest for subsistence or income generation are illegal, they still continue.
Assessment of participation of the local community vividly showed that they depend on
the forest for building poles and firewood (Waiyaki and Bennun, 2000).
2.1.2.2 The Fauna
The main mammalian fauna are the black-and-rufous giant elephant shrew Rhynchocyon
petersi Bocage 1880 (Macroscelidea: Macroscelididae) (Plate 2.3), the Zanzibar
bushbaby, Galago zanzibaricus Matschie 1893 (Primates: Galagidae) (Plate 2.4) and the
Angola black-and white colobus monkey, Colobus angolensis palliates Sclater 1860
(Primates: Cercopithecidae) (Plate 2.5) (Anderson et al., 2005). Bats are found living
and hiding in the mineshafts. These include: the rare and localized Myonycteris relicta
Bergmans 1980 (Chiroptera: Pteropopididae) (Plate 2.6 and 2.7)(BirdLife International,
2005). There is also the rare butterfly Eresinopsides bichroma.
14
Plate 2.3: Rhynchocyon petersi ( Adopted from planet-mammiferes.org).
Plate 2.4: Galago zanzibaricus (Adopted from planet-mammiferes.org).
15
Plate 2.5: Colobus angolensis palliates (Adopted from wikipedia.org).
Plate 2.6: Myonycteris relicta the fruit bat, whole body and head. Plate 2.7: Features
on the head of the fruit bat Myonycteris relicta ( Adopted from arkive.org).
2.2 Natural radiation
Mrima hill is a high natural background radiation area. The radiation is released mainly
by radioactive elements. This kind of radiation is known as ionizing radiation. Ionizing
16
radiation is produced from decaying radioactive materials which have sufficient energy to
strip away electrons from atoms. This radiation is so harmful that it can destroy any
living tissue in the human body. Generally the dose that the body is exposed to
determines the severity or type of health effects (UNSCEAR, 2008). The health effects
can be stochastic which are associated with long term and low level exposure (considered
chronic) to radiation which can cause mutation of the Deoxyribonucleic Acid and cancer
(Subhan, 2007). Children are usually more sensitive to radiation than adults because they
are growing more rapidly therefore they have more cells that are dividing and poses a
greater opportunity for radiation to disrupt the process. Most people receive a fraction of
a rem (300 mrem/yr) from background sources which are mostly radon.
Roentgen equivalent man measures the biological damage of radiation accounting for
both the amount and dose of radiation and also the effects of radiation on the living cells
in question. Exposure to a small dose of ionizing radiation to a human being over a life
time increases the chances of him/her dying of cancer than would not. The Standard unit
of dose equivalent is the sievert (Sv), conversion usually, 1 Sv = 100 rem by definition
(UNSCEAR, 2008). The conventional units for dose rate of radiation should be mrem/hr.
Regulatory limits and chronic doses are often given in units of mrem/yr or rem/yr.
Although radiation may cause cancer at high doses and high dose rates, public health data
regarding lower levels of exposure, below about 10 mSv (1,000 mrem), are harder to
interpret epidemiologically. Most of the high quality human data available is from high
17
dose exposed individuals, above 0.1 Sv, so any use of the models at low doses is an
extrapolation that might be under-conservative or over-conservative (Anand et al., 2008).
2.2.1 Thorium
2.2.1.1 Physical properties of Thorium
Thorium is the main radioactive element that is releasing radiation into the environment
in the case of Mrima hill. This element is a metal which is air-stable and retains its luster
for several months. It is white in color with silvery luster (EPA, 2013). Thorium slowly
tarnishes in air when contaminated with the oxide and becomes grey and finally black
(Wickleder, 2006). Thorium is dimorphic, changing at 1,360oC from a body-centred
tetragonal lattice form that exists at high pressure with impurities driving the exact
transition temperature and pressures (Wickleder, 2006). Thorium element is not readily
soluble in most common acids, except hydrochloric acid but it can be destroyed by water
(Hammond, 2004). However, it dissolves in concentrated nitric acid containing a small
amount of catalytic fluoride (Hyde, 1960).
2.2.1.2 Radioactivity
Thorium occurs naturally as radioactive chemical element which is found in abundance in
the soil throughout the world. Thorium atom (symbol Th) has an atomic number of 90
with 90 protons and 90 electrons, of which 4 are valence electrons. The discovery of the
element was done in 1828 and named after Thor, the Norse god of thunder (Hala and
Navratil, 2003). Thorium is found in nature as
232
Th (100%). When it decays slowly, it
18
releases an alpha particle (helium-4 nucleus). The element is estimated to be about three
to four times more abundant than uranium in the Earth‘s crust (Beck et al., 2007). It is
also a by-product of the extraction of rare earths from monazite sands. The most known
uses of thorium, for instance as a light emitting material in gas mantles or as an alloying
material in several metals, have decreased due to concerns about radioactivity. Thorium
is found in small amounts in most rocks and soils and is estimated at average of 12 parts
per million (ppm) (Hala and Navratil, 2003). In the event that thorium is inhaled it can
lead to increased risk of lung, pancreas and blood cancers due to the fact that lungs and
other internal organs can easily be penetrated by alpha particles to induce direct radiation.
Internal exposure to thorium can lead to increased risk of the liver and blood cancerous
diseases when the exposure occurs at medium and extremely high doses in humans and in
experimental animals that have been studied (UEPA, 1990).
2.2.1.3 Effects on humans
Contaminated dust, in case of thorium can be inhaled or swallowed with food or water
because as earlier enlightened, it is abundant in soil and water. Living near a thorium
contaminated site, or working in an industry where thorium is used, will increase one‘s
chance of exposure to thorium. If inhaled as dust, some thorium may remain in the lungs
for long periods of time, depending on the chemical form (van Kempen et al., 2007). The
small amount of thorium left in the body after breathing out will enter the bloodstream
and be deposited in the bones where it may remain for many years. There is some
evidence that the body may absorb thorium through the skin, but that would not likely be
the primary means of entry (UEPA, 1990).
19
The principal concern from low to moderate level exposure to ionizing radiation is
increased risk of cancer. Studies have shown that inhaling thorium dust causes an
increased risk of developing lung cancer, haemangiosoma of the liver (van Kampen et al.,
2007), and cancer of the pancreas (UEPA, 1990). Bone cancer risk is also increased
because thorium may be stored in bone. There are special tests that measure the level of
thorium in the urine, feaces, and also via exhaled air that can determine if a person has
been exposed to thorium. These tests, such as detection by imaging autoradiography
(Goto et al., 2002) are useful only if taken within a week after exposure.
2.2.2 Effects of radiation on living organisms
Different biological effects have been recorded in studies involving humans who have
been exposed to
232
Th or its related compounds such as thorotrast with varying results
(van Kampen et al., 2007) and also plants (Evseeva et al., 2003).
2.2.2.1 Polytene chromosomes and genes
Polytene chromosomes are many copy chromosomes of giant cells usually in salivary
glands of dipteran insects that have been studied widely using the fruit fly, Drosophila
melanogaster Meigen 1830 (Diptera: Drosophilidae). There is a distinction between
these types of chromosomes and the chromosomes of cells undergoing mitosis which are
diploid Drosophila cells have 8 chromosomes. The diploid are 2 copies each of 4
different chromosomes (Strickberger, 1990). In the larvae of dipteran insects, some
diploid cells stop dividing and instead grow to giant sizes as larvae grow. These giant
20
cells form much of the digestive system of the larva (Ashburner, 1989). The cells and
their nuclei increase in size as the chromosome duplicates repeatedly (polyploidy)
without accompanying cell division resulting in many copy chromosomes referred to as
polytene. Microscopic examination of several aceto-orcein stained cells showed that
chromosomes are in extended interphase of the cell cycle, and as such, are stretched out
to their full length because each chromosome actually consists of many strands, and they
are referred to as polytene (‗‗many threaded‘‘) chromosomes (Lefevre, 1974).
These chromosomes are banded, and each band (chromomere) is associated with a single
gene; each cross-band corresponds to one locus (Lefevre, 1974). Because polytene
chromosomes are extended and consist of much deoxyribonucleic acid (DNA), they are
easily visible under the light microscope. Even though radiation is known to cause gene
mutations and deletion of loci, the effects of alpha radiation emitted by
232
Th are not
known and therefore it is not known how radiation has affected vectors of disease.
2.2.2.2 The cytogenetic effects of thorium radiation on organisms
Considering that
232
Th is a soil radionuclide, most studies on the effects of this element
have been done on plant models. A study on effects of thorium by Evseeva et al. (2003)
investigated the effects of Th as a soil radionuclide and cadmium (Cd) on the short-term
(30 hours) and chronic (30 days) terms using plant models; Tradescantia L.
(Commelinales: Commelinaceae) and Allium cepa L. (Liliaceae).
The Th ion
concentration was equal to 0.18 mg/l and Cd ion-to 60 mg/l in the soil. There was
21
synergic increase of cytogenetic damage frequency in the early response of both somatic
and generative plant cells on Th and Cd combined action. During both the chronic and
short term actions, the level of genetoxicity and cytotoxic long-term effects turned out to
be lower than that of additive one. During the short-term actions, the effects are detected
by the intracellular compensating processes and in the chronic action by the mass death
of the most damaged buds in the florescence (Evseeva et al., 2003).
Another study by Soliman et al. (2011) used three plant species, Cakile maritima Scop.
(Capparales: Brassicaceae), Senecio glaucus L. (Asterales: Asteraceae) and Rumex pictus
L. (Caryopyllales: Polygonaceae), to investigate the mechanisms by which plants can
withstand high concentrations of the absorbed radionuclides. It was shown that exposure
causes decrease in the percentage of prophase and also prophase to metaphase ratio.
These included the percentage of anaphase and telophase that also increased with soil
radioactivity. The results revealed chromosome aberrations. Amino acid profiles of these
plants also indicated that radioactive elements stimulated the biosynthesis of some amino
acids such as proline, cystine, serine and thereonine while inhibiting some other amino
acids such as arginine. Aspartic acid was found to be the most abundant in the three plant
species studied (Soliman et al., 2011). All the plants models used in these studies grow
on crystalline igneous sands in Egypt with a high concentration of 232Th (Patel, 1991).
Both mosquitoes and sand flies are known to use plants as their source of carbohydrates
(Schlein and Yuval, 1987; Schlein and Muller, 2008). Not all the plant species that are
probed by these insects are known, even though some of the plants have been shown to
22
be toxic to the insects (Schlein and Jacobson, 1994). Flowering plants are usually the
favourites because of nector (Junnila et al., 2011). Tamarix jordanis Boiss 1901
(Caryopyllales: Tamaricaceae) is fed on by Culex pipiens L. (Diptera: Culicidae) (Junnila
et al., 2011), while the castor bean, Ricinus communis L. (Malpighiales: Euphorbiaceae),
the cactus, Opuntia persica var nectarine L. 1753 (Caryophyllales: Cactaceae), and
guava, Psidium guajava L. (Myrtales: Myrtaceae) are favoured by sand flies (Schlein and
Jacobson, 1994; Junnila et al., 2011). Anopheles gambiae is known to feed on plant
sugar. A study has shown that many females feed on plant sugars than males. An.
gambiae is the primary vector of Plasmodium falciparum Welch, the parasite that causes
human malaria (Fryxell et al., 2012). Mostly, male mosquitoes are known to feed on
plant-derived sugars but despite their ravid interest in blood meals, the female mosquitoes
also feed on plant derived sugars. However, the role of the plant feeding in the An.
gambiae female is poorly understood (Manda et al., 2009). The sugar may play a role in
improving their vectoral capacity by extending the female longevity. The primary source
of plant derived sugars, however is never from flowers. It is possible that in areas with
soil radionuclides, these insects could pick up radioactive elements either from the plant
sugars and/or from their breeding sites in the soil or water (Manda, et al., 2009). It is not
known how the radioactivity from the plants affects the insect.
2.2.2.3 Insect sterilization by radiation
There is literature on the success in control of trypanosomaisis tsetse fly‘s population and
the control of the African trypanosomiasis using sterile fly (Kumano et al., 2008).
According to research findings by Helsinki et al. (2006), the malaria mosquito Anopheles
23
arabiensis was studied using the Sterile technology radiation- induced sterility (STRIS).
The study included exposing male mosquitoes to gamma rays in the pupal or adult stage.
The research concluded that release of Sterile insect technology male insects was
dependant on their level of sterility and competitiveness. Both stages of the mosquito
development can be irradiated but the pupal radiation becomes easier to perform. The
sterile insect technology relies on sterilization of insect by chemosterilization, irradiation
or modern biotechnological approaches (Helsinki et al., 2006) which has not used
mosquito a lot in the researches. Treatment with ionizing radiation damages reproductive
cells as well as somatic cell. Sterilization by irradiation is still the most realistic way to
sterilize insects at present and it has used Anopheline species. It has also been used on
Aedes species, Ae. aegypti. In Ae. aegypti, the main part of spermatogenesis usually takes
place in the larval and pupal stages of development. Therefore to effectively sterilize
adult mosquito of the species, radiation dose has to be high enough to produce dormant
lethal mutation in essentially all spermatozoans (Hamady et al., 2013). This reduces the
competitiveness of irradiated mosquito males by damaging somatic cells. However, no
studies have been carried out on how high natural background radiation has affected the
mosquito populations in their natural habitat.
2.2.2.4 Sterile insect technique
Sterile insect technique (SIT) (Dyck et al., 2005; Vreysen et al., 2007) is a method of
biological control whereby a big number of sterile male insects are released into the
natural environment. Sterile insect technique is an environmentally friendly method of
insect extermination and pest management without the use of pesticides. The sterile
24
insects are usually males. The sterile males are released to the environment to compete
with wild males for female insects. If a female mates with the sterile male then it will
have no offsprings, thus reducing the next generation‘s population. In cases where high
or low doses of radiation is applied then the sterilized insects might produce new sterile
ones that are weak making them less able to compete with the wild males (Kumano et al.,
2008). However, the technique has been successfully used to eradicate the screw worm
fly Cochliomyia hominivorax in some areas of North America (Krafsur et al., 1987).
There have also been many successes in controlling species of fruit flies, most
particularly the medfly Ceratitis capitata and the Mexican fruit fly Anastrepha ludens
(Collins et al., 2008).
2.3 Species composition of mosquitoes and sand flies
2.3.1 Mosquitoes species and their infections
There are several mosquito species studied in the world some of which are of medical
importance. They are vectors of disease in the tropics. Studies have shown however, that
there is low density of vectors across sub-Saharan Africa (Onyango et al., 2013). Malaria
and Lymphatic filariasis are the most serious mosquito-borne parasitic disease. Studies
have shown that almost half of the entire human populations live at the risk of malaria
and one million deaths occur yearly particularly among children under five years of age
and pregnant women (WHO, 2000). Malaria parasites are transmitted by anopheles
females which are definitive host for the parasite.
Lymphatic filariasis is regarded the second most common global arthropod-borne
infectious disease found in humid tropical areas of Asia and Africa (Ottesen, 2000).
25
Lymphatic filarisis is caused by macroscopic nematode pathogens which are called
Wuchereria bancrofti that cause disabilities and deformities. There are three of these
parasites with Wuchereria bancrofti being the most prevalent (Manguin et al., 2009). The
parasites are responsible for all human lymphatic filarisis infection though a few are due
to Brugia parasitism. The parasites are transmitted by Anopheles mosquitoes of
approximately 70 species. Bancrotian filariasis is mainly transmitted by Culex and
Anopheles mosquito species for the nocturnally periodic form. Anopheles species are
usually in rural areas while Culex quinquefasciatus usually attack people in the tropical
urban settings.
The World Health Organization (WHO) has established two global initiatives, one for
reducing malaria and the other for lymphatic filariasis elimination dabbed Roll Back
Malaria and Global Programme to eliminate malaria and Filariasis respectively (Manguin
et al., 2009). Wuchereria bancrofti can be transmitted by mosquitoes of six different
genera including Anopheles, Mansonia, Aedes, Culex among others (Manguin et al.,
2009). In East Africa and Middle East (Egypt and Yemen), the infections is transmitted
by Cx. quinquefasciatus and Cx. pipiens. Culex pipiens species complex are mosquitoes
that are known to have morphological similarities. Culex quinquefasciatus is a member of
the complex and is adapted to living in the tropical and subtropical areas while Cx.
pipiens prefer the temperate regions. The later is found in most major cities. It transmits
Lymphatic filariasis in Pernambuco in Brazil and can also transmit several arboviruses
such as West Nile Virus and Saint Louis Encephalitis. Culex quinquefasciatus are able to
survive in polluted water where there are no natural predators (Wilke et al., 2014).
26
Mansonia uniformis are mostly found in China and Africa but Mansonia africana is
restricted to Africa. They are known vectors of arthropod-borne viruses (arboviruses)
such as Chikungunya and Rift valley fever that affect man and livestock (Labeaud et al.,
2011).
Mosquito species differ in the type of aquatic habitats they prefer for oviposition based
on location, the physicochemical conditions of water bodies which include salt, dissolved
organic matter, inorganic matter, and degree of eutrophication. The presence of potential
predators also affects habitat preference by mosquitoes (Patz et al., 2000). Anopheles
culicifacies Giles was positively associated with light and vegetation. Anopheles gambiae
in Western Kenya was associated with shallow clean water and sunlit habitats which was
the same preference for Anopheles arabiensis in Eritrea. Culex quinquenfasciatus is
important in the transmission of Bancrofti filariasis in Kenya though very little is known
about its larval ecology (Muturi et al., 2008). Few studies have reported significant
association between the genus Culex and environmental factors such as Power of
Hydrogen, canopy coverage, debris coverage and decaying organic matter. Culex
quinquefasciatus is a predominant nuisance species and potential vector of filariasis and
arboviruses in Mwea irrigation scheme in Kenya. In the study, carried out in Mwea,
which was a preliminary study in Kenya, it was revealed that the species thrived in a
variety of aquatic habitat including rice fields, canals, seepage areas, ditches, marshes,
pits and temporary pools (Muturi et al., 2008). Ecological changes affect the vectors in
their habitats. Through natural phenomenon or human intervention, there may be changes
27
in ecological balance and context within which vectors and their breed develop and
transmit infections.
When ecological stability is disturbed, it affects the vector biodiversity, abundance,
competence and human biting behavior. These include deforestation, human
encroachment, and climate and water bodies‘ location. Deforestation affects parasite
vector population and changes in the ecological niches. It also affects conditions for
proliferation of newly arriving and adaptive existing vector and their parasites. For
instance, an upsurge of malaria has been co-incidental with changes in land use and
human settlement subsequent to deforestation in Africa, Asia and Latin America (Patz et
al., 2000). Each Anopheles species occupies a unique ecological niche and operates at
different level of vector competence. The indigenous Anophelines are not able to
successfully adapt to the changes in the ecological environment. Water bodies also affect
the kind of vector species, for instance in Africa, An. gambiae prefer sunlit pools with
turbid water and no emergent vegetation while An. funestus larvae prefer clear water
without organic matter (Patz et al., 2000). Anopheles gambiae shows strong preference
for moist soil as a substrate for its oviposition rather than dry soil substrate under the
insectary conditions. In the soil, the species remains at dormant stage to resist
desiccation. An. gambiae is able to maintain a large effective population size during dry
season contrary to the suggestions that they suffer a severe population bottleneck during
the dry seasons (Minakwa et al., 2001). Aedes aegypti has increased in population with
increased urbanization which has increased sub standard housing, inadequate water,
28
sewer and waste management system in the event increasing Aedes aegypti-borne
diseases (Gubler and Clark, 1995).
2.3.2 Sand flies species and their infections
There are several species of sand flies with just a few vectors of disease. They transmit
the parasitic protozoan of the genus Leishmania responsible for leishmaniasis. The
vectors transmit infections in the tropics and subtropics. There are over thirty species of
Leishmania named to date with about ten being of medical and vetenery importance
(Bates, 2007). Sand flies pick the amastigote forms usually present in the skin of an
infected individual. They insert their saw like mouthparts into the skin and agitate them
to produce a small wound onto which blood flows from the superficial capilleries.
Amastogotes are transformed into motile promastigotes. The major syndromes in human
include; cutaneous, mucocutaneous and visceral leishmaniasis (Bates, 2007).
Ecological changes also affect leishmaniasis transmission. In some parts of Latin
America, deforestation has led to an increase in Leishmania infections (Bates, 2007).
Forests are replaced with growth of fox population which is an excellent reservoir host of
visceral leishmaniasis -Kala-azar and sylvatic leishmaniasis. Vector sand flies have
become peridomestic. Pines and gmelina trees were planted 12 years after large forests in
Para states in Brazil had been cleared. The trees were planted for paper industries, the
spiny rat which is the reservoir host for cutaneous leishmaniasis parasite had adapted to
the changed environment and became infected with Leishmania parasites (Patz et al.,
2000). Sudan was an area which was not endemic for Kala-azar but it experienced an
29
outbreak of it due to the introduction of the parasites by immigrants and ecological
changes favorable to sand flies. In the Southern Sudan, the sand flies circulate the
Leishmania parasites among small animals such as goats, sheep and dogs. The sand flies
transmit the parasites to the non-immune population entering the area, for instance, the
resettled population and refugees (Patz et al., 2000). They develop large open sores on
their faces and arms.
2.4 Vector-borne parasitic diseases in Kwale County
2.4.1 Prevalence of Malaria
Epidemiological studies have shown that falciparum malaria caused by Plasmodium
falciparum Welch 1897 is endemic along the entire Kenyan Coast. In Kwale County, this
disease is transmitted by Anopheles gambiae s.l Giles 1902 (Diptera: Anophelinae) and
An. funestus Giles 1902 (Mbogo et al., 2000; Kelly-Hope et al., 2009). In all the endemic
areas, An. gambiae has been shown to be the main vector (Mbogo et al., 2000). In this
species, the gametocyte frequency is found to be 1.3% and transmission occurs mainly
during the rainy season. These results were recorded from Amani, Viriuni, Dumbule,
Vuga, Ziwani, Tsuini, Mwaroni, Moyeni, Magaoni and Gazi (Mbogo et al., 2000) at the
Kenyan Coast. There are no available reports of malaria incidences and prevalence that
are available for Mrima hill.
2.4.2 Prevalence of Filariasis
Lymphatic filariasis is a major social and economic burden in tropical and subtropical
areas where the disease is well established. Bancroftian filariasis which is caused by
30
Wuchereria bancrofti Wucherer 1873 is also endemic in many parts of Kwale. It is the
most common form of human lymphatic filariasis and important cause of morbidity
disfiguring deformities of legs arms and genitals. It constitutes 80% of the cases reported
in developing world (India and tropical Africa) (WHO, 1992). Studies on vectors of this
disease have shown that mosquitoes found infected with W. bancrofti larvae are
Anopheles gambiae and Anopheles Funestus. Culex quinquefasciatus Say 1823 is also
involved in the transmission of the parasite (Mwandawiro et al., 1997).
The prevalence of infection may be on the increase due to inadequate sanitation leading
to favourable conditions for the breeding of vector mosquitoes (Ottesen and
Ramachandran, 1995). The overall prevalence of microfilaraemia in the population is
16.4% as has been shown in villages that were sampled including Gandini, Dzivani and
Lutsangani (Njenga et al., 2000). Several infections of P. falciparum and W. bancrofti
have also been detected in mosquitoes in Kwale (Muturi et al., 2006). It has also been
shown that An. gambiae is the main vector for both malaria and lymphatic filariasis in
both Kilifi and Kwale areas (Kelly-Hope, 2009).
Entomological investigations done at the Kenyan coastal region have reported that An.
gambiae Sensulato, An. funestus and Culex quinquefasciatus are the vectors involved in
transmission of lymphatic filariasis (Mwandawiro et al., 1997; Pederson and Mukoko,
2002). Culex quinquefasciatus is known to breed in a variety of stagnant water habitats
where water has been significally polluted like in cess pits and canals near houses with
long bathroom sewage water (Njenga, 2011; WHO, 2013). As one moves deep into the
31
rural areas, anopheles mosquitoes become predominant and are the principal vectors in
the rural coastal villages in East Africa (Njenga, 2011). It has however, been found that
very little or no attention has been paid to the disease in many countries because data on
the magnitude of the problem does not exist (WHO, 1992). No data is available on
infection and transmission of malaria and lymphatic filariasis around Mrima hill.
2.4.3 Prevalence of Leishmaniasis
Even though there are no records to show that there is leishmaniasis in Kwale County,
Phlebotomine sandflies were first reported in Mombasa on the Kenya Coast in 1912
(Mantuefeel, 1921). Later in 1930 and 1932, Sinton identified and reported the presence
of Sergentomyia schwetzi Adler, (Theodor and Parrot), S. africana Newstead, S. yusafi
Sinton and S. bedfordi congolensis Bequaert & Walravens (Sinton, 1930; Sinton, 1932).
2.5 Present study
Based on the literature review on the species population and composition of both
mosquitoes and sand flies, it is clear that such studies have been conducted in many
places in Kenya including the coastal regions and particularly in Kwale County but none
has been conducted in Mrima hill. Given that malaria and leishmaniasis are prevalent in
other regions neighbouring Mrima hill, it was important to carry out research to establish
the population and species composition of mosquitoes and sand flies as well as the
infection rates in Mrima hill.
32
CHAPTER THREE: MATERIAL AND METHODS
3.1 Study area
Mrima hill is located in Msambweni location in Kwale County, a distance of 70
kilometers south of the City of Mombasa in the Coast of Kenya (390 16.00‘ E, 40 28.00‘
S) (Figure 3.1). People living in the area were mostly peasant farmers practicing both
small scale farming and animal keeping. Sampled
study sites were areas inhabited by
humans around the Mrima hill and homesteads in areas showing radiation levels that
were above the normal level of 240 mrems. Sources of water in the area of study included
boreholes and swamps with radioactivity which was 50 times higher than the normal
natural background radiation as reported by Patel (1991).
3.1.1 Location of Mrima hill
Mrima hill is a Forest Reserve which is a mixed coastal forest located in Msambweni
Location of Kwale County with an altitude of 58 m above sea level (asl), a distance of 70
kilometers south of the City of Mombasa in the Coast of Kenya. The forest is
undifferentiated and has exceptional plant species diversity (BirdLife International,
2005). The coastal plain of Kenya slopes gently seaward and Mrima hill rises from 90 m
asl on the northern point to 296 m asl at the highest point near the centre of the hill
(BirdLife International, 2005). The hill is ellipsoidal in plan and has a long axis running
NW – SE and is approximately 3 Km long and 2.1 Km wide at the widest point. Two
small plateaus form the top of hill with elevations of 300 metres and 285 metres,
respectively, and are separated by a narrow col. The col broadens out to form a wide
shallow valley to the north east. This part of the coastal region is known as the low
33
plateau and lies to the west of the coastal plain at altitudes ranging between about 30
metres to 135 metres asl.
Figure 3.1: Map of mrima hill area where the study was carried out in Kwale
County – Kenya ( www.Google maps.com).
34
Though most of this region is low lying and very gently rising towards the west, the
Mrima hill highest point is averagely 300 metres asl (NEMA, 2001).
The total annual rainfall ranges between 965 mm to 1270 mm. The rainfall pattern is
characterized by two distinct long and short rainy seasons (bimodal) corresponding to
changes in the monsoon winds. The long rains occur from April to July and average
1,100 mm with a peak of 330 mm in May and correspond to the South Easterly
monsoons. The short rains are usually experienced in October to December which
corresponds to the North Eastern monsoons, which are comparatively dry. January and
February are the driest months. Rainfall decreases as one moves inland, away from the
influence of onshore winds, with some areas receiving as little as 965 mm per year. Also
those areas on the leeward side of the two hills (Mrima and Dzombo) have slightly less
rainfall. The area experiences high temperatures with an annual mean of 27.90C (NEMA,
2001). The hottest month is February with a maximum average of 33.10C. The coolest
month is July with a minimum of 22.70C. The area is generally hot and humid all the year
round due to the high evaporation rate. As Mrima hill is close to the sea the humidity is
usually high, except in the three dry months (NEMA, 2001). Mrima hill images are
shown in Plate 3.1.
35
Plate 3:1: Images of Mrima hill a) View of Mrima hill from the North East side. b) View of
Mrima hill the South West side. c) View of Mrima hill from the South East side (Adapted
from NEMA, 2001).
36
3.2 Pilot study
Pilot study was carried out in the area around the month of April 2011. The physical
observation of the area was done including the area‘s humidity and temperature using
weather recording instruments such as barometer and thermometer respectively. The
people were generally lean. Oral interview was done on the inhabitants who confirmed
that there were cases of malaria in the area. Parasitological information from the Mrima
Health Centre for the same period as that of mosquito and sand fly sampling in Mrima
hill area revealed Malaria positive diagnosis on people who had not travelled to endemic
areas lately. The population mostly slept outside especially men and not many household
slept under treated mosquito nets.
3.3 Sampling procedure
The study adopted the formulae by Yates et al. (2008) as shown below
P =1-N-1/N N-2/N-1…..N-n/N- (N-n)
Cancelling =1-N-n/N
= n/N
=100/1000
=10%
The total number of houses in the study area was 384. Taking ten percent of that gave a
sample size of 38 houses. A number of households were randomly selected and the
radiation levels taken using hand held Digilert 100 CPMs reader and recorded. Selection
criterion was based on the total numbers of homesteads in the study area. A total of 12
homesteads with 38 houses were randomly sampled in the village. Human biting night
37
insects (mosquitoes and Phlebotomine sand flies) were trapped for five consecutive days
during the rainy season in August 2011 using Solid State Army Miniature (SSAM) light
traps (John W. Hock Co., Gainsville, Florida U.S.A). Depending on the numbers of
houses in each homestead, a light trap was suspended outside each house to trap peridomestic diptera entering or leaving the houses. The traps were set up one hour before
sunset (6.00 pm) because that is usually the time when most dipterans are active and
dismantled at 0.5 h after sunrise (6.00 am) as described by Johnson et al. (1993). The
trapped insects were kept in papercups and transported every morning to the Kenya
Medical Research Institute (KEMRI)‘s Kwale Station Laboratories for processing. They
were sorted and identified to species level. Plates 3.1 and 3.2 below show the setting of
light traps in the hill and around the households for trapping mosquitoes and sand flies.
Plate 3.2: A light trap set in the upper part of the hill for trapping mosquitoes and
sand flies.
38
Plate 3.3: A light trap suspended outside a house for trapping mosquitoes and sand
flies.
3.4 Laboratory procedures
3.4.1 Specimen preparation and staining with Giemsa stain
The mosquitoes and sandflies were dissected into thin films and placed on microscopic
slides to air dry before being fixed in absolute methanol for 5 minutes. The fixing was
done by first immersing it in absolute methanol to prevent disintegration of the tissues on
the slides after which the slide was immersed in a freshly prepared 10% Giemsa stain
solution for 30 minutes. The slide was then flushed with tap water and left to air dry
before observing it using the light microscopy.
39
3.4.2 Preparation of chloral hydrate mounting gum
Chloral hydrate gum, which is usually used to make clear sand fly specimens, was
prepared according to the method described by Minter (1964). Eight grams of gum
Arabic and 70 grams of chloral hydrate crystals were weighed. They were dissolved in a
mixture of distilled water, glycerine and glacial acetic acid. The mixture was stirred using
a magnet stirrer and then left to stand for one hour for uniformity. It was then ready to be
used to mount the adult sand flies.
3.4.3 Procedure for mounting specimen using chloral hydrate mounting gum
A drop of the gum was placed on a slide and mounted on a dissecting microscope before
being brought into focus. The sand fly sample was put in the middle of the drop. A pin
was used to orient it in the correct position and to make it sink into the gum. Another
drop was placed on a cover slip and inverted onto the slide that had the sample so that the
two drops came into contact. This was to prevent the formation of bubbles. The gum was
left for 24 hours to stand to enable it to spread all over the covered region on the slide.
The excess gum was removed by placing a piece of cotton wool on the side of the slide so
as to absorb it. The features on the specimen were observed using the dissecting
microscope.
40
3.5 Species identification using anatomical features
3.5.1 Mosquitoes
Mosquitoes that were captured from the study site were separated by genera using a
binocular microscope. They were identified using the standard taxonomic keys as
described by Gilles and de Meillon (1968).
3.5.2 Sand flies
Any caught female sand flies were washed in 2% liquid soap detergent in normal saline.
They were then dissected using pins and a dissecting microscope on ice cold microscope
slides before mounting for taxonomy. This was done in order to minimize the chances of
motile parasites such as promastigotes in the sand flies dying. All the females caught in
all the collection sites were dissected. The heads and genitalia of sand flies were mounted
using chloral hydrate gum, covered with cover slips and allowed to dry (these are the
parts used for identification of sand flies). Mounted sand flies were left to clear overnight
before identification using the taxonomy keys as described by Abonnenc and Minter
(1965).
3.6 Examination for parasites
All female mosquitoes (131) and sand flies (30) were dissected in a drop of sterile, cold
phosphate-buffered saline (PBS) on sterile slides and examined for the presence of
parasites in the salivary glands in the case of mosquitoes, and in the guts of sand flies
using light microscopy. Slides used for the dissections were further stained with Giemsa
for examination of parasites. Giemsa is a differential stain which differentiates the
nucleus of merozoites. The merozoite nucleus stains pink.
41
3.7 Data Analysis
Comparison of the numbers of mosquitoes and sand flies caught against different levels
of radiation was done by Pearson Chi-square test. The relationship of both mosquito and
sand fly species and the radiation levels per site and the relationship between radiation
and elevation were done using Pearson correlation using the procedure of Statistical
Package for the Social Sciences (SPSS) VER 20 (2011).
42
CHAPTER FOUR: RESULTS
4.1 Composition of trapped mosquitoes and sand flies
4.1.1 Mosquitoes
The total number of mosquitoes collected was 131. Culex pipiens L was the most
abundant at 91 insects, caught from most of the study sites accounting for 69.42% of the
total catch. This species was caught in 9 out of the 12 sampling sites at various elevations
ranging from an elevation of 33 masl at site 4 up to 82 masl at site 6 and within natural
radiation ranging from 5.9 mSv/yr at site 7 to 17.5 mSv/yr at site 4. Mansonia africana
Theobald were 24 in number which accounted for 18.32% of the total population of
insects caught. The species was collected in only 3 sites, namely 6, 9 and 10 with
elevations of 82, 51 and 44 masl and radiation levels of 8.3, 12.2 and 9.9 mSv/yr
respectively. Mansonia uniformis Theobald was the next in abundance at 12 insects in
total accounting for 9.16% of the total mosquitoes caught and was only collected in site 2
which had an elevation of 45 masl and a radiation level of 7.97 mSv/yr.
Aedes aegypti L. and Culex vansomerenae Edwards comprised of 2 insects each
accounting for 1.53% each of the total collected mosquitoes. The former was collected in
site 3 which had an elevation of 30 masl and a radiation level of 6.48 mSv/yr; whereas
Culex vansomerenae was only collected in site 9 which had an elevation of 51 masl and a
radiation level of 12.2 mSv/yr. In all these households where the collections of
mosquitoes were carried out, despite the fact that the trapping was done during the rainy
season, no Anopheles Giles species was caught. This was also despite the differences in
43
radiation levels that ranged from the lowest 5.9 mSv/yr to the highest 17.5 mSv/yr that
were recorded. Therefore, no vector of disease was caught (Table 4.1).
Table 4.1: Number of mosquito species collected, their percentage, elevation (m
(ASL) and radiation levels (mSv/yr) around the Mrima study area
Site
Elevation Radiation Species
m(ASL)
(mSv/yr)
75
10.08
Cx. pipiens
45
7.97
Cx. pipiens
M. uniformis
30
6.48
Cx. pipiens
Aedes aegypti
33
17.5
Cx. pipiens
74
10.9
None
82
8.3
Cx. pipiens
M. africana
92
5.9
Cx. pipiens
65
6.5
Cx. pipiens
51
12.2
Cx. vansomerenae
M. africana
44
9.9
Cx. pipiens
M. africana
38
9.7
Cx. Pipiens
68
7.9
None
Frequencies Percentages
%
1
31
23.66
2
2
1.53
12
9.16
3
3
2.29
2
1.53
4
9
6.87
5
0
0
6
31
23.66
8
6.1
7
1
0.76
8
10
7.63
9
2
1.53
1
0.76
10
2
1.53
15
11.45
11
2
1.53
12
0
0
Totals
131
100
m(ASL) – metres above sea level, mSv/yr – milliSieverts per year, The numbers in
parentheses are percentages of the total catch per site.
44
4.1.2 Sand flies
Throughout the entire collection period, in all sites, a total of 39 phlebotomine sand flies
were collected. In the study area, only Sergentomyia Franca and Parrot species were
collected. Out of these sand fly species, Sergentomyia (Sergentomyia) bedfordi was the
most abundant species comprising of 29 insects in number and 74.36% of the total catch.
Other species that were collected were Sergentomyia (Parvidens) suberecta at 6 insects
accounting for 15.38% of all them caught. A total of 2 Sergentomyia (Grasomyia)
meilloni was caught accounting for 5.12% of the total sand fly population caught,
Sergentomyia (Parvidens) inermis and Sergentomyia (Sergentomyia) schwetzi were the
lowest species caught at a single one each which accounted for 2.56% of the total sand
fly species collected. No sand flies harbored parasites and none was blood fed. Only one
(1) male Sergentomyia bedfordi was collected in site 5 while all the other sand flies from
the other sites were females. There was no Phlebotomus rondani species caught from the
study site. Among the sand flies caught none was a known vector of diseases in Kenya
(Table 4.2).
45
Table 4.2 Number of Sand fly species collected, their percentage, elevation (m (ASL)
and radiation levels (mSv/yr) around the Mrima study area
Site
Elevation Radiation Species
m(ASL) (mSv/yr)
75
10.08
S. meilloni
S. suberecta
S. bedfordi
45
7.97
None
30
6.48
S. bedfordi
33
17.5
None
74
10.9
S. bedfordi
82
8.3
S. schwetzi
S. bedfordi
92
5.9
None
65
6.5
None
51
12.2
None
44
9.9
S. inermis
38
9.7
None
68
7.9
None
Frequencies Percentages
%
1
2
5.13
6
15.38
22
56.41
2
0
0
3
2
5.13
4
0
0
5
1
2.56
6
1
2.56
4
10.25
7
0
0
8
0
0
9
0
0
10
1
2.56
11
0
0
12
0
0
Totals
39
100
m(ASL) – metres above sea level, mSv/yr – milliSieverts per year, The numbers in
parentheses are percentages of the total catch per site.
46
4.2 Relationship between number of mosquitoes and sand flies
The radiation levels recorded ranged from the lowest 5.9 mSv/yr to the highest 17.5
mSv/yr whereas elevation levels were recorded from the lowest at 30 m(asl) to the
highest at 92 m(asl). Pearson Chi-square statistical test on the number of sand flies and
number of mosquitoes collected in Mrima hills indicated that there was no significant
association between the two variables ( the number of mosquitoes did not relate to the
number of sand flies) (2 =36; df=35; p=0.165; Figure 4.1).
Figure 4.1 Relationship between number of mosquitoes and sand flies
47
4.3 Relationship between levels of radiation and number of mosquitoes and sand
flies
4.3.1 Relationship between levels of radiation and number of mosquitoes
Pearson Correlation analysis on radiation (mSv/yr) and number of mosquitoes collected
per site indicated that there was no significant correlation between the two variables
(r=0.026; df=10; p=0.937; Figure 4.2, Appendix I).
Number of mosquitoes
Levels of radiation
Figure 4.2: Relationship between levels of radiation and numbers of mosquitoes in
Mrima hill.
48
4.3.2 Relationship between levels of radiation and number of sand flies
Pearson Correlation analysis on the radiation (mSv/yr) and number of sand flies collected
per site indicated that there was no significant correlation between the two variables
(r=0.031; df=10; p=0.923; Figure 4.3, Appendix II).
Number of sand flies
Levels of radiation
Figure 4.3 Relationship between levels of radiation and numbers of sandflies in Mrima
hill.
4.4 Relationship between levels of radiation and elevation
There was variation between elevation and radiation (Table 4.5). There was no significant
correlation between elevation and radiation (r = -0.389; df = 10; p = 0.211; Figure 4.4,
Appendix III).
49
Levels of elevation
Levels of radiation
Figure 4.4 Relationship between levels of radiation and levels of elevation in Mrima hill
4.5 Vector infection rates
None of the species of both mosquitoes and sand flies trapped and dissected from the
study area were infected by parasites of malaria, lymphatic filariasis, mosquito-borne
arboviruses or leishmaniasis.
50
CHAPTER FIVE: DISCUSSION
5.1 Trapped mosquitoes and sand flies
5.1.1 Mosquito species
The results from the present study indicated that population of both mosquitoes and sand
flies in Mrima hill was relatively low and the medically important species of the vectors
in Kenya were not found despite the fact that it was during rainy season. The study
expected to report availability of the vectors of diseases and a higher number of both
mosquitoes and sand flies than reported previously in studies from the neighboring subcounties.
The study area had poor sanitary disposal system which could explain the high number of
Culex pipiens. According to Syed and Leal (2009), Culex pipiens (the common house
mosquito) is usually the most common pest mosquito in urban and suburban settings and
an indicator of polluted water in the immediate vicinity. The presence of Cx. pipiens
brought the assumption that the level of pollution in the present study area was
questionable and therefore, needed to be investigated. Several studies (Wayne, 2013)
have shown that the mosquito species lay eggs in batches in polluted or foul water where
the larval development takes place in places like septic seepage and other dirty water
sources. Lutomia et al. (2013) has shown Culex pipiens to be a competent vector of West
Nile Virus in the laboratory and has also been found in nature to be infected by the virus.
Culex vansomerenae Edwards was found in very low numbers in Mrima hill. The
mosquito species has been shown to be susceptible to infection with Wuchereria
51
bancrofti. However, according to findings by Kinyatta et al. (2011), it does not develop
disseminated infection that is necessary for transmission. It is therefore, unlikely that
there could be Wuchereria bancrofti transmission taking place within the study area.
Culex Vansomerenae has been shown in the laboratory to be susceptible and able to
transmit West Nile Virus (WNV) (Lutomia et al., 2011). Even though this mosquito
species was found in very low numbers, Mrima hill should be considered an area for
West Nile Virus surveillance.
Mansonia africana was reported in a higher number than the related species, Mansonia
uniformis. It is quite difficult to morphologically distinguish between the two species
using the taxonomic key. Interestingly, Mansonia africana was mostly caught in sites
with high elevation and moderately high radiation whereas Mansonia uniformis was
collected at low levels of elevation and relatively low levels of radiation even though
radiation and elevation did not significantly affect the availability of the mosquito species
caught from the study area. Mansonia uniformis are mostly found in China and Africa
but Mansonia africana is restricted to Africa. They are known vectors of arthropod-borne
viruses (arboviruses) such as Chikungunya and Rift Valley Fever that affect man and
livestock in Kenya as reported in earlier studies (Labeaud et al., 2011). Even though
studies have shown that the two mosquito species are active transmitters of Wuchereria
bacrofti in Ghana according to Ughasi et al. (2012), polymerase chain reaction done in
Kenya has shown that Mansonia africana and Mansonia uniformis caught in Kwale
County are not susceptible to infection with the parasite (Kinyatta et al., 2011).
52
Studies on abundance and bionomics of Aedes aegypti L have been conducted in various
parts of the Coastal regions of Kenya (Teesdale, 1955) apart from Mrima hill. Aedes
aegypti can be disseminated by ground transportation therefore being able to spread
dengue virus beyond the normal flight range of the mosquitoes. They were in low
numbers in the present study and it is possible to conclude that the presence of the Aedes
aegypti in low numbers was due to transportation in vehicles to the study area, however,
the fact needs to be investigated. According to WHO (2006), both the females and male
adults of this mosquito feed on nectar of plants; however, female mosquitoes need blood
in order to produce eggs and they are active during day time. It is reported by Fontenille
et al. (1997) to be an important domestic pest (associated with humans and their
dwellings) but it is medically important as a major vector for the yellow fever virus and
dengue virus as accounted by Johnson et al. (1982). An outbreak of dengue fever caused
by dengue type 2 virus was reported around the coastal towns of Malindi and Kilifi in
Kenya (Johnson et al., 1982). It is possible that outbreaks of the two viral diseases can
occur in Mrima hill if the population of Aedes aegypti became high.
The present study established absence of Anopheline mosquitoes irrespective of the
recent report by (Njenga, 2011) suggesting that the deeper one gets into the rural areas,
the better the chances of getting Anopheles mosquitoes as they are the predominant and
principal vectors in the rural coastal villages. Njenga (2011) concurred with the findings
of (Mbogo et al., 2000), that there were Anopheles mosquitoes in Kwale County.
Unfortunately, the current study was carried out during rainy season but did not report
any Anopheles mosquitoes despite the fact that the mosquito is a perennial fly, abundant
53
mostly during rainy seasons because of availability of their preferred breeding habitats.
The absence of anopheline mosquitoes in Mrima hill could have been due to effects of
radiation on fertility and fecundity of the insects. It was interesting to note that there was
also no mosquito species infected with malaria parasites or filarial worms among the
collected species from the present study area.
Lack of rivers in Mrima hill left residents with only one option, boreholes as the only
sources of water which is normally salty. This may explain why there were no fresh water
sources which could be used as breeding sites by Anopheles mosquitoes. Poor sanitary
conditions are also normally considered less conducive for Anopheles breeding (Gilles
and Coetzee, 1987). Pollutants were observed in the study area which could have
contributed to the lack of Anopheles gambiae mosquito species in the study area.
However, recent work in other parts of Africa have shown that Anopheles gambiae
larvae can develop in polluted temporary pools in peri-urban areas ( Awolala et al.,
2007). In another rescent study in other parts of the world (Keating et al., 2004),
Anopheles gambiae larvae were collected mainly in temporary habitats containing
pollutants such as detergent, human and animal faecal waste and an assortment of
domestic debris, an indication that Anopheles gambiae has adapted to tolerating
pollutants in breeding environments. It was therefore not clear why Anopheles mosquito
species were not found in the present study given that their larvae can survive in polluted
habitats. World Health Organization (2010) reported the fact that Anopheles mosquitoes
can flourish in any environment as being responsible for rising malaria incidences.
Therefore, considering the absence of Anopheles mosquitoes in the study area, it is
54
unlikely that transmission of malaria and lypmphatic filariasis can take place through
these species. The results obtained from the present study at Mrima hill have shown that
Cx. vansomerenae, Cx. pipiens and Aedes aegypti are the only mosquito species of
medical importance caught but did not harbor any parasites of diseases.
5.1.2 Sand fly species
As reported by Lewis (1974), Sergentomyia species have been shown to have a feeding
preference for reptiles and amphibians and are not known to be susceptible to Leishmania
parasites that cause human disease (Lawyer et al., 1990). Sergentomyia bedfordi is
known to be a perennial species in other parts of Kenya such as Baringo District and is
the most abundant during the dry season and prefers resting mainly in areas with tree
canopys (Basimike et al., 1991). Mutinga (1975) reported observations from trapping
using Disney traps around Mt Elgon that showed that Sergentomyia bedfordi can be
found in all types of buildings, but has never been reported to bite humans.
It has also been reported by Kan et al. (2004) to be attracted particularly to goats, Capra
hircus L in the Masinga, Mukusi area of Machakos County. This could explain why this
species is the most abundant around Mrima hill, where almost every homestead kept
goats within their compounds. Field and laboratory studies have shown that Sergentomyia
bedfordi feeds on the skink Mabuya striata Peters (Reptilia: Scincidae) and gets infected
with Trypanosoma boueti Leger and Leger (Kinetoplastida: Trypanosomatidae). A study
report by Ashford et al. (1973) showed the parasites can develop up to the epimastigotepromastigote stage in the foregut but the sand fly cannot transmit it through the bite.
55
Transmission to the skink, which is a reptile, occurs when it feeds on the infected sand
fly. Sergentomyia suberecta was first reported within Coast Province by Sinton (1932).
The species was collected in Mrima hill but there were no prior records of parasite
isolation from it. Similarly, the few that were caught had no infections. Its bionomics is
poorly known.
In Kenya, Sergentomyia schwetzi is found in two forms, the typical and the atypical,
depending on the structures of the seventh and eighth abdominal tergites. The typical
form was found in Mrima hill. Laboratory studies have shown that it cannot support the
development of Leishmania major Yarkimoff and Schokhor and therefore cannot
transmit the parasite (Lawyer et al., 1990). This species has been shown to be susceptible
to infection with Rift Valley Fever Virus following oral infection but it cannot transmit
the virus to a clean Syrian hamster, Mesocricetus auratus Warehouse (Dohm et al.,
2000). Apart from the possibility of this sand fly becoming a biting nuisance, it can be of
no major problem to the residents of Mrima hill.
Sergentomyia meilloni which occurred in Mrima hill is also mainly found in Coastal
regions of Kenya with a few in Eastern regions of Kenya (Anjili et al., 2011). Little is
known about the bionomics of this species and also its preferred feeding host. There are
no records showing that any parasite has ever been isolated from it. Considering that it
was found in very low numbers (5.13%), it is possible that it also possess no major threat
to the Mrima hill population. Further studies need to be done to establish whether it can
bite man and also to establish whether it is susceptible to viruses of human concern.
56
5.2 Infection rates
It was not clear why there were no parasites of diseases present in the species of
mosquitoes and sand flies caught and dissected from the study area. It could be probably
due to the fact that the medically important species trapped from the study area are not
known to transmit infections in Kenya.
5.3 Relationship between radiation and elevation
Since there was no significant relationship between radiation and elevation and also
between radiation and species of both mosquitoes and sand flies in Mrima hill it remains
unknown whether radiation affected the species composition of both mosquito and sand
flies in their natural habitat. In the present study, the effect of natural radiation on species
of both mosquitoes and sand flies was not established.
57
CHAPTER SIX: CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
i.
Mosquito species composition in Mrima hill comprised: Cx. pipiens, Cx.
vansomerenae, M. uniformis, M. africana and Ae. aegypti. From what is known
about the species compositions of mosquitoes around study area, apart from Culex
vansomerenae and Culex pipiens, which are of medical importance, the potential
of an outbreak of diseases to occur can be considered very remote.
ii.
The sand fly species which were collected from Mrima hill included: S. meilloni,
S. suberecta, S. bedfordi, S. inermis and S. schwetzi. They are not of medical
importance in Kenya. Most of the species were Sergentomia which have reptiles
and amphibians as feeding preference as discussed. Transmission of
leishmaniases is also considered remote because no parasite was found in the
dissected insects.
iii.
Through dissections, microscopic examination of wet and Giemsa stained slides
of mosquitoes the study did not detect any malaria or filarial worms.
iv.
There were no Leishmania parasites detected. It cannot be accurately concluded
that this was as a result of the elevated levels of radiation in the study area.
58
v.
The radiation readings recorded from the geiger counter indicated the highest
radiation level as 17.5 mSv/yr at elevation 33 masl yet the annual limit of
effective dose is equivalent to 5.0 milliSieverts. The elevation levels of Mrima hill
ranged from as low as 30 masl to the highest at 82 masl. The elevation had no
significant relationship with the radiation level as done by the Pearson
correlations.
6.2 Recommendations
i.
From results of this study it is recommended that the trapping of more insects
over an extended period of time during different seasons be done. This method
will generate period prevalence data that will help understand the epidemiology of
disease transmission in the study area. This could provide more information on
the possibility of collecting the possible disease vectors in the area.
ii.
Trapping of insects should be extended to cover a wider area than only in Mrima
hill. This is because road construction materials from the quarries on Mrima hill
have been used to construct roads in many sections of Kwale County.
iii.
Studies should be carried out on the effect of radiation on the dipteran arthropod
tissues to see if there is any evidence in their polytene chromosomes or aberration
of their DNA.
59
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APPINDICES
APPENDIX I: Mosquitoes Pearson Correlation between Elevation and Radiation
Elevation(m(ASL)
Radiation(mSv/yr)
Pearson Correlation
Sig. (2-tailed)
N
Pearson Correlation
Sig. (2-tailed)
N
Elevation(m(ASL)
1
17
-.259
.315
17
Radiation(mSv/yr)
-.259
.315
17
1
17
70
APPENDIX II: Sand Flies Pearson Correlation between Elevation and Radiation
Elevation(m(ASL)
Radiation(mSv/yr)
Pearson Correlation
Sig. (2-tailed)
N
Pearson Correlation
Sig. (2-tailed)
N
Elevation(m(ASL)
1
15
-.360
.187
15
Radiation(mSv/yr)
-.360
.187
15
1
15
71
APPENDIX III: Pearson Correlation between Elevation (m(ASL) and
Radiation(mSv/yr)
Elevation(m(ASL)
Radition(mSv/yr)
Pearson Correlation
Sig. (2-tailed)
N
Pearson Correlation
Sig. (2-tailed)
N
Elevation(m(ASL)
1
12
-0.389
.211
12
Radiation(mSv/yr)
-.389
.211
12
1
12