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Anthropod borne(Arbo) Viruses
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Arthropod- borne Viruses
• Def:Arthropod-borne viruses (arboviruses) are
viruses that can be transmitted to man by
arthropod vectors
• Is a group of infectious viruses (agents) that are
transmitted by blood sucking arthropods from
one infected vertebrate host to another
• They can multiply in the arthropods without
causing any damage or disease.
Arthropod borne Viruses
• An arthropod acquires virus through ingestion of
blood from viremic vertebrate
• All arboviruses have an RNA genome and lipid
contained envelope
• They are inactivated by ether or sodium
deoxycholate
• Most of individual viruses are named after disease
or after geographic area where were first isolated
• ( dengue,yellow fever or West Nile fever,Zika
fever etc).
Arthropod borne Viruses
• Despite being common in tropical rain forests
they are also found in temperate areas
• There are more than 350 arboviruses based on
antigenic groups
• Chemical and physical properties are also used to
group them.
• Many of them are grouped under
toga,bunya,reo,arena,picorna and rhabdovirus
groups.
• Arboviral diseases are seasonal and regional
based on life cycle of the vectors
Arthropod borne Viruses
• Inclusion in group is based on ecological and
epidemiological hence has viruses of diverse
physical and chemical properties
• Classification:
Arboviruses belong to three families
1. Togaviruses e.g. EEE, WEE, and VEE
2. Bunyaviruses e.g. Sandfly Fever, Rift
Valley Fever, Crimean-Congo Haemorrhagic Fever
3. Flaviviruses e.g. Yellow Fever, dengue,
Japanese Encephalitis
Hemorrhagic Fever Viruses:
Taxonomy
Arenaviridae
Argentine HF
 ( Junin Virus)
Bolivian HF
(Machupo
Virus)
Venezuelan HF
(Guanarito
Virus)
Brazilian HF
(Sabia Virus)
Lassa Fever
Rodents
Bunyaviridae
Rift Valley
Fever
Crimean-Congo
HF
Hantavirus
Genus
HFRS
Filoviridae
-Ebola
HF
-Marburg HF
¨TickBorne:
¨Kyasanur
Mosquitoes
Flaviviridae
Forest
Disease (KFD
Virus)
¨Omsk HF ( OHF
Virus)
¨Mosquito-Borne:
Yellow Fever
West Nile Fever
Dengue HF
Arthropod-borne viruses
Transmission Cycles:
• Man - arthropod -man
• e.g. dengue, urban yellow fever(Reservoir may be in
either man or arthropod vector)
• Latter transovarial transmission may take place
• Animal - arthropod vector – man
• e.g. Japanese encephalitis, EEE, WEE, jungle yellow
fever.
• The reservoir is in an animal
• Virus is maintained in transmission cycle involving
arthropod vector and animal. Man becomes infected
incidentally.
Man-Arthropod-Man Cycle
Animal-Arthropod-Man Cycle
Arthropod-borne viruses
• General properties: The arboviruses share some
common biological properties
All members produce fatal encephalitis in
suckling mice after intracerebral inoculation
They possess haemagglutinin and agglutinate
erythrocytes of goose or day-old chicks
They can be grown in tissue cultures of primary
cells like chick embryo fibroblasts and in cultures
of appropriate insect tissues
Arthropod-borne viruses
They may also be isolated in the yolk sac or CAM
of chick embryo 5.
In general, arboviruses are readily inactivated at
room temperature and by bile salts, ether and
other lipid solvents
Examples of Arthropods are:
Aedes aegyti , Culex Mosquito, Ixodid Ticks,
Phlebotomine Sandfly
Some of arthropod Vectors
Mosquitoes: Diseases transmitted
Japanese encephalitis, dengue, yellow fever, St.
Louis encephalitis, Zika fever, Ebola, VEE etc.
Ticks:
Crimean-Congo haemorrhagic fever, various tickborne encephalitides etc.
Sandflies:
Sicilian sand fly fever, Rift valley fever.
Some of Arthropod Vectors
Aedes Aegyti
Assorted Ticks
Culex Mosquito
Phlebotmine Sandfly
Some animal reservoirs
In many occasions the actual reservoirs are unknown.
but the following animals are implicated :
•Birds: Japanese encephalitis, St Louis encephalitis
•Pigs: Japanese encephalitis
•Monkeys: Yellow Fever
•Rodents: VEE,Russian Spring-Summer encephalitis
Arboviral diseases
1. Bunyaviridae
2. Flaviviridae
Arbovirus encephalitis:
•
•Other:
Arbovirus encephalitis:
La Crosse encephalitis (LCV) ·
California encephalitis (CEV)
Viral hemorrhagic fever:
Rift Valley fever (RVFV)
Japanese encephalitis (JEV) ·
 Australian encephalitis (MVEV, KUNV) ·
 St. Louis encephalitis (SLEV) ·
West Nile fever (WNV)
•Viral hemorrhagic fever:
Dengue fever (DV)
Yellow fever (YFV) ·
 Zika fever
3.Togaviridae
– Arbovirus encephalitis:
 Eastern equine encephalomyelitis (EEEV) ·
 Western equine encephalomyelitis (WEEV) ·
Venezuelan equine encephalomyelitis (VEEV)
O'Nyong-nyong Virus ( OV ) - UGANDA
Chikungunya (CV) - TANGANYIKA
 Ross River fever (RRV)
1. Bunyaviridae
Viral hemorrhagic fever:
Crimean-Congo hemorrhagic fever (CCHFV)
2. Flaviviridae
Arbovirus encephalitis:
Tick-borne encephalitis (TBEV) ·
 Powassan encephalitis (PV) ·
Deer tick virus encephalitis (DTV)
Viral hemorrhagic fever:
Omsk hemorrhagic fever (OHFV) ·
Kyasanur forest disease (KFDV/Alkhurma virus)
3.
Reoviridae
 Colorado tick fever (CTFV)
1. O'Nyong-nyong Virus (OV)
– Vector: - Mosquitoes
-Togaviridae, Genus: Alphavirus closely related to Chikungunya viruses
– The O'nyong-nyong virus - First isolated by Uganda Virus
Research Institute, Entebbe - Uganda in 1959.
– The name is from Nilotic language of Uganda and Sudan
(means “weakening of the joints.”)
– Transmitted by an infected mosquito.
– Clinical signs are polyarthritis, rash and fever, eye pain,
chest pain, lymphadenitis and lethargy.
– No deaths due to infection are known so far.
O'Nyong-nyong cont….
Epidemics:
• Two epidemics of O’nyong’nyong fever: 1st occurred in
1959 to 1962, extending from Uganda, Kenya, Tanzania,
DRC, Malawi and Mozambique, >2 Mil people were
infected. Is among the largest epidemics recorded.
1st virus isolates were obtained from mosquitoes &
human blood samples from Gulu - Northern Uganda in
1959.
• 2nd epidemic in 1996-1997 in 400 people were confirmed
in Uganda. The 35-year hiatus between the two outbreaks
and evidence of an outbreak in 1904-1906 in Uganda
indicates a 30-50 year cycle for epidemics.
Chikungunya Virus
• Vector : Mosquitoes (Aedes aegypti)
1955
• Discovery in Tanganyika (along border btn Mozambique and
Tz), 1952,
Name from Makonde word- kungunyala, meaning to dry up or
become contorted, meaning( " which bends up“)
Occasional outbreaks in Africa, South Asia, SE Asia,
Recently over a wider range.
Example:
- On 28 May 2009 Thailand - Provincial hospital first
chikungunya infected women – Premature infected baby
- Many confirmed cases in South India in 2009
•
Common Symptoms: Fever 40 °C, petechial/maculopapular
rash of the trunk and limbs, arthralgia/polyarthritis
headache, conjunctitis,& Slight photophobia.
Chikungunya cont……
• CHIKV illness symptoms are similar to dengue
fever
NB: Chikungunya was one of more than a dozen agents that
the United States researched as potential biological
weapons before the nation suspended its biological
weapons program
Rift Valley Fever Virus
• Vector: Mosquitoes
• The viral agent is an
arbovirus, belongs to the
Phlebovirus genus in the
Bunyaviridae family.
RVF- Virus cont….
• It causes Rift Valley Fever (RVF), an arthropod-borne,
acute fever-viral disease primarily of sheep, goats, cattle
can also affect humans.
Mainly a
disease of
sheep
ABORTION
• RVF in Africa causes abortions in sheep, cattle and goats
high mortalities in lambs and generalized disease in man.
RVF- Virus cont…
• Clinical sign: Normally victims are +/- symptoms or mild
illness with fever, headache, myalgia and liver
abnormalities.
• Few cases (< 2%) illness progress to Hemorrhagic fever
syndrome, Meningoencephalitis, or affecting the eye.
• Ill patients experience fever, generalized weakness, back
pain, dizziness, and weight loss at onset of the illness.
Patients recover within 2–7 days after onset.
• Appr.1% of sufferers die of the disease
• Rift Valley fever was one of more than a dozen agents that
the United States researched as potential biological
weapons before suspended its biological weapons
program
Yellow Fever Virus
Flaviviridae Family:
• A 40 to 50 nm enveloped RNA virus
• Causative agent of Yellow fever ( an acute viral hemorrhagic
disease).
• Transmission: Bite of female mosquitoes ( Aedes aegypti,
and other species) Found in tropical and subtropical in
(South America and Africa) not in Asia.
• The hosts of the virus are primates and several species of
mosquito.
• The origin of the disease likely to be Africa, from where it
was introduced to South America during slave trade in the
16th century.
• Since 17th century, major epidemics recorded in Americas,
Africa & Europe. In 19th century yellow fever was one of the
most dangerous infectious diseases
Yellow Fever Virus cont….
Signs:
• I. Period : 3 - 6 days
• Most cases present with mild fever, headache, chills, back
pain, anorexia, nausea and vomiting.
• The infection lasts only three to four days. 15% of cases
enter a second, toxic phase of the disease with recurring
fever, accompanied by jaundice due to liver damage, and
abdominal pain.
• Bleeding in mouth, eyes & GIT can cause vomitus
containing blood (giving the name black vomit).
Yellow Fever Virus….
• Toxic phase is fatal in approximately 20% of cases,
making the overall fatality rate for the disease 3%
• Surviving the infection causes life-long immunity
normally no permanent organ damage
• No therapy is known so far, vaccination programs are,
along with reduction of mosquito vectors population,
in affected areas.
• Since the 1980s, the number of cases of yellow fever
has been increasing, making it a reemerging disease.
Dengue Virus
• Dengue virus (DENV) one of four serotypes is the
causative agent of dengue fever.
• A mosquito-borne single positive-stranded RNA
virus of the family Flaviviridae; genus Flavivirus.
• All four serotypes can cause the full spectrum of
disease
Dengue Virus cont….
• Dengue fever ( breakbone fever)
• Is an acute febrile infectious disease caused by the
dengue virus.
• Symptoms include headache, a characteristic skin rash,
muscle & joint pains; in small proportion the disease
progresses to life-threatening complications ie:
• Dengue hemorrhagic fever (which may lead to severe
hemorrhage) and dengue shock syndrome
• So a very low blood pressure can cause organ
dysfunction).
•Transmission: Mosquitoes Aedes aegypti, and
rarely Aedes albopictus.
•The virus has four different serotypes, an infection with
oneserotype gives lifelong immunity to that type, but
short-term immunity to others.
•Currently no available vaccine,
•Measures to reduce the habitat , mosquitoes population
& limiting exposure to bites, are useful to decrease the
incidence of dengue.
Treatment: Currently no approved vaccines for the dengue
virus
For Mild or moderate dengue disease:
•Treatment is supportive, using either oral or intravenous
rehydration ,
For severe cases:
•Intravenous fluids and blood transfusions
•The rate of infection has increased dramatically over the
last 50 years, with around 50–100 million people being
infected yearly.
•Is a global disease currently is endemic in more than
110 countries.
• Early descriptions of the condition is from 1779, and its
viral cause and the transmission were elucidated in the
early 20th century.
Arthropod-borne viruses
• Diagnosis
• Serology: Useful in diagnosis of arboviral
infections.
• Culture: – Some cell lines are used, including
mosquito cell lines. But , rarely carried out as
pathogens are group 3 or 4.
• Direct detection tests: - Detection of antigen and
nucleic acids are done but there are safety issues.
Prevention(General)
• Surveillance :- Of disease and vector populations
• Control of vector: - Pesticides, elimination of
breeding grounds.
• Personal protection: - Screening of houses, bed
nets, insect repellants.
• Vaccination - Available for a number of arboviral
infections e.g. Yellow fever, Japanese encephalitis,
Russian tick borne encephalitis