Download Faculty of Allied Medical Sciences Parasitology

Faculty of Allied Medical
Sciences
Parasitology
(MLPR-201)
fall 2013/2014
Arthropods as Vectors of the
Etiologic Agent of Diseases
Dr. Hamdy Badie M. El-Wakil
Prof. of Parasitology & Public Health .
Faculty of Allied Medical Sciences.
Pharos University In Alexandria,Egypt
Intended Learning outcomes
• By the end of this lecture the student should
understand Arthropods as Vectors of the
Etiologic Agent of Diseases
C - General Characters of Arthropods:
• All arthropods, while varying considerably in size and
shape, have certain features in common. They are all
bilaterally symmetrical and metamerically
segmented. They have externally a hard chitinous
exoskeleton, sometimes sclerotized or calcified,
inside which a hollow blood cavity is containing a
clear fluid haemolymph. Arthropods have an
excretory system, but a few of them consist of the
malpighian tubules (2 or more), which lie in the
hemocele and open into the hindgut near its junction
with the midgut. They discharge the liquid wastes
into the hindgut.
• Respiration may be achieved by a variety of
methods e.g. via gills, lung books, gaseous
exchange, through the cuticle or by means of
spiracles. Circulatory system consisting of heart,
aorta, and sometimes-paired blood vessels that
opens into the hemocele, which extends into all
parts of the body. The blood consists of plasma
and amoeboid white cells; respiratory pigment is
hemocyanin in the plasma rather than
hemoglobin in the case of gill routing and book
lung-breathing.
• The forth system, called central nervous system which
consists of a dorsally situated composed of dorsal and
ventral fused cephalic ganglia "Brain" connected by
circumesophageal commissures to the media ventral paired
nerve trunk, and to twinned ganglia of each post-cephalic
body system. Nerve fibers extend from the central nervous
system to all important organs and tissues. Either in many
groups, there are light-sensitive organs in the head
individual eyespots (ocelli) or compound eyes composed of
ommatidia. All arthropods have jointed appendages, which
may take the form of legs, antennae, mouthparts or cerci.
The sexes are always separates and morphologically
distinguishable.
Two different types of development take place:
• 1- Incomplete metamorphosis: Hatched
larvae resemble the adults but are smaller and
gradually increase in size by successive
molting e.g. Ticks.
• 2- Complete metamorphosis: Hatched larvae
are completely different morphologically from
the adults. They may be worm like, transform
to the inactive pupal stage from which finally
the adults emerge , e.g. House fly.
D-Arthropods of medical importance:
• They are Included in the Following Classes:
• i- Class Insecta or Hexapoda e.g. house fly, fleas, lice, bugs,
mosquitoes and flies (venomous, biological and mechanical
vectors, intermediate hosts, and parasitic.
• ii- Class Archanida e.g. scorpion, spiders, ticks and mites.
• iii- Class Crustacea e.g. crabs, prawns and copepods.
• iv. Class Chilopoda e.g. censpodes (venomous).
• v. Class Pentatomida e.g. tongue worms (Endoparasitic).
Relation of the Pathogen to its Host:
• The broad sense of the word, in one way or another
may be considered parasites. The arthropod itself as
a parasitic or else it transmits a parasitic infection.
• 1- Ectoparasites: parasites, which live either
temporally or permanently on the outside of the
body e.g. the lice.
• 2- Endoparasites: which live within the body e.g.
Tongue worms (Pentastomida).
• 3- Obligatory parasites: This forced to remain during
their entire life in or on the body of the host e.g.
both biting and sucking lice.
• 4- Facultative parasites: which are able to exist
as free-living organisms and they can be live as
parasites e.g. the larvae of blowflies and flesh
flies.
• 5- Intermittent parasites: which prey upon the
host only at time and are free-living during
intervals between meals e.g. bed bugs.
• 6- Transitory parasites: which are refer to cases
in which the organism is parasitic during only a
part of its life history e.g. Bot flies.
• Parasites are adapted to their mode of life in two
general respects; physiologically and
morphologically
The Arthropod-Transmitted Pathogens:
• The groups of parasites served by arthropods are as follows:
• 1- Protozoa: e.g. Entamoeba, Plasmodium, Trypanosoma and
Leishmania. Several different groups of insects are involved as
vectors for these protozoans’ diseases.
• 2- Helminthes: e.g. tape worms, flukes, round worms and
spiny-headed worms. Arthropods may be involved either as
vectors or as intermediate hosts.
• 3- Bacteria: e.g. Pasterurella (plague and tularemia bacilli),
Shigella (dysentery), Salmonella, and others. Several groups of
arthropods are involved as vectors.
• 4- Spirochaetes: e.g. Treponema pertenue, the causal
agent of Yaws, transmitted sometimes by flies and
Borrelia recurrentis, the causative agent of Relapsing
fever, transmitted by lice (Pediculus humanus) or Ticks
(Ornithodorus spp.)
• 5- Bastonella bacilliformis: the causal agent of Carrion's
disease transmitted by Phlebotomus.
• 6- Richettsiae: the causal agent of Typhus, scrub typhus,
spotted fever, Q. fever and related infections; louse, mite,
or tick.
• 7- Viruses: The causal agents of yellow fever, dengue the
encephalitade and related infection of Colorado tick fever,
phlebotomus fever and others. Mostly mosquito-born,
but ticks phlebotomine sand flies and perhaps other
vectors are involved.
Vector Effectiveness:
• The variability in vectors effectiveness is attributed to several factors that
are:
• 1- Longevity: as long as the life of vector has been extended, this helps it
to transmit the pathogens.
• 2- Pathogen receptivity: the availability of vector to transmit the pathogen
and the pathogen found it suitable for development or suitable habitat.
• 3- Host specify : host preference.
• 4- Frequency of feeding.
• 5- Mobility and rate of speed.
• 6- Numbers.
• 7- Physiological and behavioral plasticity.
• 8- Absence or presence of natural enemies.
• 9- Vertical transmission; Transovarian transmission.
• 10- Vectorial capacity; means that all the previous factors are all together
in the same place and the same time.
Assignments
• Group of students are selected every
week to prepare a short seminar about
his/her point of interest in one of the
lecture topics. That to be
•Recommended text books:
• World Health Organization, Geneva. Basic laboratory methods in medical
parasitology. 1991.
• Larry Roberts and Jr.,John Janovy. Foundations of Parasitology. 2009
• Burton J. Bogitsh and Clint E. Carter. Human Parasitology. 2010