Ar-bo-viruses

1. ARBOVIRUSES
ARTHROPOD BORNE VIRUS

2. ARBOVIRUSES
 Arthropod borne viruses – virus of vertebrates.
 Transmitted by insects vectors.
 Cause infections in animals & birds.
 Transmitted to man by bite of infected mosquitoes, ticks & sand flies.
 Worldwide, more in tropical areas than temperate.
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Transmission Cycles
 Man – Arthropod – Man
 Animal – Arthropod - Man

3. Man-Arthropod-Man Cycle
 Reservoir may be in either man or arthropod vector.
 E.g. dengue, urban yellow fever.
 In the latter transovarial transmission may take place.
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4. Animal-Arthropod-Man Cycle
 The reservoir is in an animal.
 The virus is maintained in nature in a transmission cycle involving the
arthropod vector and animal. Man becomes infected incidentally.
 e.g. Japanese encephalitis, EEE, WEE, yellow fever.
Both cycles may be seen with some arboviruses such as yellow fever.
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5. Animal Reservoirs
In many cases, the actual reservoir is not known. The following animals
are implicated as reservoirs.
Birds - Japanese encephalitis, St Louis encephalitis, EEE, WEE
Pigs - Japanese encephalitis
Monkeys - Yellow Fever
Rodents - VEE, Russian Spring-Summer encephalitis
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6.  About 500 viruses in this group.
 About 100 causes infection in man.
 About 10 in India.
 Sub groups: Alpha virus ( Toga viruses)
Flavi virus
Bunya virus
Rhabdo virus
Reo virus6
Examples of
Arthropod Vectors
Aedes Aegypti Ticks
Culex Mosquito Phlebotmine Sandfly

7. Morphology
 Size : 60-150nm
 Symmetry: Spherical .cubical, helical
 Genome: ss RNA (Reoviridae -ds RNA)
 Distribution: Worldwide. Many diseases given names according to location.
Eg: Venzulean Equine Encephalitis, Japanese B encephalitis. St. Louis enc.
Virus, Russian spring summer Enc., California enc. etc
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8. General Properties:
 Causes fatal encephalitis in suckling mice after intracerebral inoculation.
 Possess haemagglutinin and agglutinate erythrocytes of goose or day old chicks.
 Mosquito borne arboviruses multiply in aedes and culex, while tick borne multiply in
Ixodid ticks.
 They can be grown in cell like chick embryo fibroblasts or continuous cell lines like vero
or HeLa, & in cultures of appropriate insect tissues.
 May also be isolated in the yolk sack or CAM of chick embryo.
 They are readily inactivated at room temperature and by bile salts, ether and other lipid
solvents.8

9. Antigenic Structure:
 Three antigens are important in serological studies namely:
a. Haemagglutinins
b. Complement fixing antigen
c. Neutralizing antigen
 Cross reactions occur among arboviruses.
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Pathogenesis
 Virus enters the body through bite of the vector.
 Virus multiplies in reticuloendothelial system and leads to viraemia.
 Virus transported to target organs such as CNS – encephalitis;
 Capillary endothelium – haemorrhagic fevers & Liver – Yellow fever.

10. Diseases Caused
 Febrile illness - This is usually a non-specific illness resembling a number
of other viral illnesses such as influenza, rubella, and enterovirus infections.
The patients may go on to develop encephalitis or haemorrhagic fever.
E.g. Chikungunya, Dengue.
 Encephalitis – Inflammation of brain.
E.g. EEE, WEE, St Louis encephalitis, Japanese encephalitis.
 Hemorrhagic fever – Bleeding disorder with high fever.
E.g. yellow fever, dengue hemorrhagic fever.10

11. Arbovirus infections
Family & Genus Encephalitis Febrile illness Haemorrhagic fever
I. Togaviridae
Alphavirus
(Mosquito – borne)
•WEE
•EEE
•VEE
•Chikungunya
•O’nyong-nyong
•Semliki Forest
•Sindbis
•Ross river virus
•Chikungunya
II. Flaviviridae
Flavivirus
a. Mosquito- borne
b. Tick-borne
•St. Louis Encep.
•Ilheus
•West Nile
•Murray Valley Enc.
•Japanese B Enc.
•Russian spring summer
enceph.
•Powassan
•Dengue, types 1-4 •Dengue
•Yellow fever
•Kyasanur forest
disease
•Omsk Haemorrhagic
fever
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12. Family & Genus Encephalitis Febrile illness Haemorrhagic fever
III. Bunyaviridae
a) Bunya virus
(Mosquito-borne)
b) Phlebovirus
(Phlembotomus or
mosquito-borne)
c) Nairovirus (tick-
borne)
•California encephalitis
•La Crossie
•Chittor virus
•Sandfly fever
•Rift-valley fever
•Nairobi sheep
disease
•Ganjam virus
----
IV. Reoviridae
Orbivirus
(Tick-borne)
-------- •Colorado tick borne
virus ----
V. Rhabdoviridae
Vesiculovirus
(Mosquito-borne,
sandfly-borne)
--------
•Vesicular stomatitis
virus
•Chandipura virus
----
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13. TOGAVIRIDAE
 Toga = Mantle
(cloak, a Roman dress)
 Spherical, enveloped, 60-70 nm in diameter with
icosahedral capsid surrounded by lipoprotein envelop and
contains single stranded RNA.
 Contains 2 genera: Alphavirus & Rubivirus
 Alphavirus- 32 members, 13 cause human infection.
 Rubivirus contains Rubella virus, is not arthropod borne.13

14. Encephalitis viruses:
 EEE (Eastern Canada, USA & the Caribbean)
 WEE (America)
 VEE (Central & South America)
 Causes encephalitis in horses & humans.
 Influenza like illness with encephalitis in less cases.
 Culex & Anopheles mosquitoes (vectors).
 Formalin inactivated mouse brain vaccines (for EEE & WEE), Live
attenuated vaccines (VEE).
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15. Viruses causing Febrile illness:
1. Chikungunya virus:
 First isolated from human patients and Aedes aegypti
mosquitoes in Tanzania in 1952.
 Transmitted by Aedes aegypti.
 Appeared in India in 1963.
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FEATURES:
•Fever, crippling joint pains, conjunctivitis, lymphadenopathy & rash.
•Patients lies doubled up (severe joint pains) hence the name.
•Hemorrhagic manifestations may occur.
•Biphasic fever with period of remission after 1-6 days.
•No animal reservoir & No vaccines available so far.

16. 2. O’nyong-nyong virus:
 Isolated in Uganda. Confined to Africa.
 Closely related to Chikungunya virus antigenitically.
 Transmitted by Anopheles species.
3. Semliki Forest virus:
 First isolated in 1942 in Uganda from Aedes mosquitoes.
4. Sindbis Virus:
 Isolated from Culex mosquitoes in Sindbis district of Egypt in 1952.
 Recovered from Africa, India, Australia & Phillippines.
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17. FLAVIVIRIDAE:
 Flavus = Yellow (refers to yellow fever)
 Originally named as group B arboviruses.
 Contains over 70 viruses, 13 causes human infection.
 Mosquito and Tick borne.
 Non-arthropod-borne viruses of this family belong to 2 genera: Pestivirus
(veterinary pathogens) and Hepatitis C virus.
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Morphology:
 Spherical 40 – 50 nm in diameter.
 Single stranded RNA.
 Inner viral core is surrounded by a lipid envelope which is covered with
glycoprotein and matrix or membrane protein.

18.  Korea, Japan, S/E Asia, India.
 Recognized in Japan since 1871.
 Virus first isolated in Japan in 1935.
 Named JE- B to differentiate it from JE-A (von Economos disease).
 JE is a serious disease. Signs of encephalitis seen after 1 - 6 days.
 S/S of encephalitis- Neck rigidity, convulsion, coma. CSF pressure increased,
lymphocytes- increased, sugar-Normal, proteins-increased, Chlorides-Normal.
 Mortality- up to 50%. Residual neurological damage.
Japanese encephalitis:
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19.  Japanese Encephalitis appeared in India in 1955.
 Pigs act as amplifier hosts.
 Hosts: Herons & ergrets ( birds), ducks, pigeons, sparrows, cattle.
 Transmitted by- Culex mosquito.
 Preventive measures:
 Relocate piggeries away from dwellings.
 Mosquito control.
 There is no satisfactory vaccine.
 Treatment: No specific treatment.
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20. Yellow Fever
 Confined to Africa, Central and South America.
 Immunization necessary for Air travel to these countries.
 Yellow fever does not indicate Jaundice, but the Yellow quarantine flag used
by the ships during 17th century to warn the presence of infection on board.
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21. Distinctive features
 Recognised in 17th century
 Originated in Africa » » » Europe, America
 Transmitted by Aedes aegypti mosquitoes
 Incubation period is 3-6 days.
 Fever, headache, vomiting, chills, jaundice,
albuminuria, hemorrhages.
 Liver/kidney failure
 Liver- fatty degeneration and necrosis. Councilman
bodies. Eosinophilic inclusion bodies in nucleus.
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Fatty degeneration of Liver
. Eosinophilic inclusion bodies
Counsilman bodies

22. Dengue
 Name derived from the Swahili, Ki denga pepo,
meaning a sudden seizure by a demon.
 Widely distributed.
 Affects 2.5 billion people in 200 countries.
 4 serotypes: DEN1, DEN2, DEN3 & DEN4.
 Transmitted by Aedes aegypti mosquitoes.
 Antigenitically related to yellow fever, but no significant cross immunity.
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23. Clinical Features:
 Affects usually older children and adults.
 Incubation period is 3 -14 days.
 Sudden onset, fever, headache, muscle pain
retrobulbar pain, pain in back and limb (break bone
fever) on 3rd or 4th day.
 Lymphnode enlargement, and maculo -papulary
rash.
 Febrile illness lasts for about 10 days, after which
recovery is generally complete.
 Rarely fatal.
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24. Complications
 Due to multiple dengue virus.
 Hemorrhages in skin, mucosa, internal organs
(Dengue Hemorrhagic Fever)
 Pulmonary edema.
 Low BP.
 Liver cirrhosis.
 Shock – Dengue Shock Syndrome.
 Mortality - 5 to 10%
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 Elimination of mosquitoes and mosquito breeding places.
 No specific treatment.
 No effective vaccines available.
 Live attenuated vaccine containing all 4 dengue serotypes is under clinical trials.
Prophylaxis:

26. Kyasanur Forest disease
 Disease first recognized in Kyasanur forest in Karnataka in 1957.
 Severe prostrating illness.
 Reservoirs - Birds & animals. Tick may act as the reservoir.
 Transmission – by bite of Tick.
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Clinical features:
 Incubation period: 3 – 7days
 Patient develops fever of sudden onset.
 Headache, vomiting, conjunctivitis, myalgia and sever prostration.
 Massive hemorrhages in alimentary canal, chest cavity and epistaxis may
occur.
 Case fatality – 5%.  Vaccination – killed KFD vaccine.

27. BUNYAVIRIDAE
 Contains more than 300 members.
 First isolated from
Bunyamwera in Uganda.
 About 100 nm diameter.
 Has complex structure, with
a triple segmented genome of ss RNA.
 Contains 4 medically important genera-
Bunyavirus, Phlebovirus, Nairovirus & Hantavirus.
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28. 1. Bunyavirus: Mosquito-borne. It includes California encephalitis virus,
La Crossie virus & Chittor virus. Clinical features similar in all three except that
Chittor virus causes only mild fever.
2. Phlebovirus: Phlebotomus or mosquito borne. Causes Sandfly fever & Rift
valley fever. 20 antigenic types, only 5 causes human infection. No vertebrate
hosts other than humans.
3. Nairovirus: Tick borne. Mainly the disease of sheep. Infects humans
occasionally causing mild febrile illness.
4. Hantavirus: Non-arthropod-borne. Transmitted to humans by rodents hosts.
Causes haemorrhagic fever and nephropathy. Also named HFRS (Haemorrhagic
fever with renal syndrome). Clinical picture resembles Leptospirosis & typhoid.
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29. Lab diagnosis of Arbovirus diseases
 Specimen: Blood, CSF, Brain may be used for virus isolation.
 Virus isolation:
1. Intra cerebral inoculation in suckling mice. Most sensitive. Develops fetal
encephalitis.
2. Yolk sac of chick embryo
3. Tissue culture
4. Xenodiagnosis (a method of animal inoculation using laboratory-breed bugs and
animals)
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Serology:
 ELISA – Used for detection of serotype specific IgM antibody.
 Complement fixation test.
 Haemagglutination or neutralisation test.

30. Treatment:
 Antibiotics are not effective for treatment and no effective antiviral drugs have
yet been discovered.
 Treatment is supportive, attempting to deal with problems & other treatable
complications.
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VACCINES:
 The only effective vaccine available is for Yellow fever .
 It is a live attenuated vaccine known as 17 – D strain .
 The vaccine is administered subcutaneously in one dose , with a booster dose
every 10 years .
 Recommended to travelers to endemic areas.
 Should not be given to children less than 9-months.