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Arboviruses: togaviridae, flaviviridae, bunyaviridae

a. Togaviridae-
Spherical, 70nm diameter, positive sense, single stranded RNA, enveloped

Two genera:
  • Alphavirus: arthropod borne viruses
  • Rubivirus: rubella virus, not arthropod borne
Human diseases caused by alphaviruses
Virus Vertebrate reservoir Mosquito vector Disease
Eastern equine encephalitis Wild birds Culiseta, aedes, culex Encephalitis
Western equine encephalitis Wild birds Culex Encephalitis
Venezuelan equine encephalitis Horses Aedes, culex Encephalitis
Chikungunya Monkeys, humans Aedes Fever, rash, arthralgia, myalgia
Onyong-nyong Humans Anopheles Fever, rash, arthralgia, myalgia
Mayaro Monkeys Haemagogus Fever, rash, arthralgia, myalgia
Ross river Marsupials, rodents Aedes, culex Fever, rash, arthralgia, myalgia
Sindbis Wild birds Culex, culiseta, aedes Fever, rash, arthralgia, myalgia
Laboratory diagnosis
Intracerebral inoculation of suckling mice
Isolation: tissue culture (vero, C6/36 mosquito cell line), detection of growth by immunofluorescence
Serology: ELISA, HAI, CFT, Nt
b. Flaviviridae- Spherical, 40-50nm, single-stranded, positive sense RNA

Two genera of medical importance
  • Flavivirus: arthropod borne viruses
  • Hepacivirus: Hepatitis C virus, non-arthropod borne
Human diseases caused by flaviviruses
Syndrome Vector Virus
Encephalitis Mosquito Japanese encephalitis
Murray valley encephalitis
St. Louise encephalitis
West Nile virus
Tick Louping ill
Russian spring summer encephalitis
Yellow fever Mosquito (Aedes aegypti) Yellow fever
Dengue Mosquito (Aedes aegypti) Dengue 1,2,3,4
Haemorrhagic fever Mosquito (Aedes aegypti) Dengue 1,2,3,4
Tick Omsk haemorrhagic fever
Kyasanur forest disease
Laboratory diagnosis
  • Intracerebral inoculation of suckling mice
  • Isolation: tissue culture (vero, C6/36 mosquito cell line), detection of growth by immunofluorescence
  • Serology: ELISA, HAI, CFT, Nt
i. Japanese encephalitis
  • 1st case seen in Japan. Also Seen in Korea, Japan, SE-Asia, India
  • Vector is Culex tritaeniorhyncus which breeds in rice fields
  • Amplifier hosts - Pigs & herons (Water birds)
  • Vaccine - live Attenuated Inactivated
ii. Yellow fever
  • Yellow as it causes jaundice
  • Disease of tropical America & Africa
  • Not reported from Asia including India.
  • 2 forms in forest / Sylvate cycle -Runs between monkeys & mosquitoes
  • Urban cycle — Man and Aedes aegypticus mosquito
  • Virus multiplies in kupffer cells - jaundice & decreased prothrombin formation
  • Hematemesis & malena -Renal failure & death
  • Vaccine -3 Line Attenuated vaccine K/a 17 D vaccine
  • Protection for 10 years.
iii. Dengue
  • 4 serotypes 1 -4. Incubation, period - 5-8 days.
  • Infection with one serotype gives partial immunity to infection with other serotypes
  • Vector - Aedes mosquito
  • Reservoir - Man & Monkey
  • C/F - Classic dengue - Saddle back fever,
  • Break bone fever. (severe pain in back, msls, joints. A maculopapular rash appears on trunk & spreads to face & extremities.
  • Complete recovery
  • Effects older children & adults
Dengue Haemorrhagic fever –
  • When a person previously infected by one. serotype is now infected by a different serotype, then enhanced infection - haemorrhages.
  • Dengue shock syndrome -
  • DHF / DSS in 2 age groups -
  • 5-- 10 years - 6-9 months
  • Vaccine Under trial - 5-- 10 years
iv. Kavasanur Forest Disease (KFD)
  • Epidemic in Karnataka in 1957
  • Epizootic in Monkeys -) fatal disease
  • Forest birds and small mammals are reservoirs
  • Tick - Haemophysalis spinigera is vector
  • Monkeys - Amplifier host
  • In humans accidental infection
  • Fever with massive haemorrhages in GIT & chest & nose
  • Vaccine ---> Killed vaccine
v. West Nile fever
  • Reservoir host -3 Birds
  • Vector -a Culex mosquito
  • C/F -~ Dengue like illness rarely encephalitis
  • Lab diagnosis of Flavi viruses-Mice inoculationCell cultureIgM ELISA
vi. Bunyaviridae
  • Spherical, 80-120nm diameter, triple segmented, negative sense or ambisense, ss RNA, enveloped
  • Four important genera
  • Bunyavirus: predominantly transmitted by mosquitoes
  • Nairovirus: predominantly transmitted by ticks
  • Phlebovirus: predominantly transmitted by sandflies
  • Hantavirus: rodent borne, not transmitted by arthropods
Human diseases caused by members of the family bunyaviridae
Genus Virus Vector Human disease
Bunyavirus La Crosse Mosquito Encephalitis
Oropouche Mosquito Fever, arthralgia, myalgia
Phlebovirus Rift valley fever Mosquito Fever, myalgia, retinitis, hemorrhagic fever
Sandfly fever Sandfly Fever, myalgia, conjunctivitis
Nairovirus Crimean-Congo hemorrhagic fever Tick Hemorrhagic fever
Hantavirus Hantaan - Hemorrhagic fever, nephropathy
Belgrade - Hemorrhagic fever, nephropathy
Seoul - Nephropathy
Puumala - Nephropathy
vii. Retroviridae
Spherical, 80-100nm, cylindric core, single stranded RNA, linear, positive sense, diploid, enveloped. Reverse transcriptase enzyme makes DNA copy from genomic RNA

Human Retroviruses
Subfamily Genus Virus Disease
Oncovirinae Retrovirus HTLV1 Adult T cell leukemia
HTLV2 Infection in intravenous drug users, not associated with any disease
Lentivirinae Lentivirus HIV1
Spumavirinae Spumavirus Human foamy virus
Not associated with any disease

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