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In the past, arboviruses were organized into one of four groups: • A, B, C and D. • Group A denoted members of the genus Alphavirus, Group B were members of the genus Flavivirus,and Group C remains as the Group C serogroup of the genus Orthobunyavirus.
Group D was renamed in the mid-1950s to the Guama group and is currently the Guama serogroup in the genus Orthobunyavirus. • This renaming of the group was because the number of groups would eventually exceed the length of the alphabet. • Since then, the organization of arboviruses into these groups has fallen out of usage as the standard biological classification system became more preferred for classifying viruses
Arbovirus is a term used to refer to a group of viruses that are transmitted by arthropod vectors. • The word arbovirus is an acronym (ARthropod-BOrne virus). • Symptoms of arbovirus infection generally occur 3–15 days after exposure to the virus and last 3 or 4 days.
The most common clinical features of infection are fever, headache and malaise, but encephalitis and hemorrhagic fever may also occur. • The word tibovirus (TIck-BOrne virus) is sometimes used to describe viruses transmitted by ticks, a superorder within the arthropods.
Placed in Togariridae Flaviviridae. Bunyaviridae Reoviridae Rhabdoviridae.
Vectors :Mosquitoes. Ticks. Phlebotomus less common. Culicoides Cimicidae
SYMPTOMS: • The incubation period - the time between when infection occurs and when symptoms appear - varies from virus to virus, but is usually limited between 2 and 15 days for arboviruses. • The majority of infections, however, are asymptomatic.
Among cases in which symptoms do appear, symptoms tend to be non-specific, resembling a flu-like illness, and are not indicative of a specific causative agent. • These symptoms include fever, headache, malaise, rash and fatigue. Rarely, vomiting and hemorrhagic fever may occur. • The central nervous system can also be affected by infection, as encephalitis and meningitis are sometimes observed.
Prognosis is good for most people, but is poor in those who develop severe symptoms, with up to a 20% mortality rate in this population depending on the virus. • The very young, elderly, pregnant women and people with immune deficiencies are more likely to develop severe symptoms.
Common Properties : 1. Suckling mice - Encephalitis 2. Chick embryo - CAM yolk sac. 3. Growth in Tissue cultures Primary - Chick embryo fibroblasts. Continuous cell lines - vero / Hela. Insect tissue.
4. Haemagglutination - goose chick. 5. Inactivated - RT. Bile salts, Ether. 6. Serology : ELISA, CFT, HAI, NT. (SerotypeIgM)
Zoonoses : Maintained in animals Expect Dengue, O nyong. Nyong Animals - asymptomatic Vector - biting a viremic vertebrate Extrinsic IP. Human infection Vectors Reservoir animal
Preliminary diagnosis of arbovirus infection is usually based on clinical presentations of symptoms, places and dates of travel, activities and epidemiological history of the location where infection occurred.
Definitive diagnosis is typically made in a laboratory by employing some combination of blood tests, particularly immunologic, serologic and/or virologic techniques such as ELISA, complement fixation, polymerase chain reaction, neutralization test and hemagglutination-inhibition test.
Toga virus : Enveloped, spherical, single Str. RNA Replicates in host cell cytoplasm. Alpha virus : Rubivirus HAI - Not specific Neutralisation test - More specific
Encephalitis Viruses : [America] Eastern equine encephalitis Western equine encephalitis Venezuelanequineencephalitis Culex & Anopheles. Wild birds - reservoirs. Sudden onset of fever
CSF :Pleocytosis Protein, sugar levels - Normal. Febrile illness : Chikungunaya : Aedesaegypti 1963 in India - As epidemics Calcultta, Madras.
O nyong, nyong: Uganda. (Africa) Anopheles mosquito Resembles chikangunaya
Mayaro virus : (WI, SA) similar disease Simliki Forest virus : Uganda, Aedes mosquito Sindbis Virus : India - 1952
Ross river virus : Epidemic polyarthritis - Australia. Flavi viruses : Encephalitis viruses : Reservoir : wild birds. St. louis encephalitis. USA
West Nile - India. (dengue like) (Karnataka ) horses JBE Murray Valley encephalitis (Australia)
Haemorrhagic fevers : Dengue types 1-4 -( Aedes aegypts) Mosquito Yellow fever - Kyasanur Forest disease Tick Omsk haem. Fever - (Ixodid tick) Both
Russian spring summer encephalitis Louping ill - Scotland Ixodid ticks. Leaping gait sheep.
2. Powassan virus : Tick. Canada North USA. Japanese ‘B’ encephalitis: Japan 1871. Isolated 1935 Encephalitis lithargica (JAE) Epidemics. Summer - autumn Culex. Tritaeniorhychus
Pathogenesis : I phase : Viral multiplication in neuronal tissue. Seen in blood 3 days before CNS inv.
II phase:(Major illness ) Viral multiplication in CNS Injury destruction. Lesions in basal structures Cerebral cortex. SC Small haemorrhages. PV cuffing.
Lab diagnosis :First 1 - 3 days of illness . PS :Neutrophilia CSF :Pleocytosis (lymphocytes ) Viral isolation.
Epidemiology : Asymptomatic 500 – 1000 inapparentinfe / every case. Mortolity 50% oldage 80% Residual neur. Damage - 50%
India : 1955 from vellore. Children. Epidemics Oct” - Nov” South India. Upto 1973
Vaccines : 1. Formaline inactivated MBV. 2. Primary baby Hamster kidney cell vaccine. (Live attenuated) Two doses : 2 wks interval Booster - 6 – 12 m. Immunity - short lived.
Dengue : Tropics & subtropics. Exists in 4 types (1 - 4 ) IP : 2 - 15 days. CF : ac. Fever. Biphasic (saddle – back form) Headache, retrobulbar pain pain in back, limbs - Break bone fever.
Lymphadenopathy. Maculopapular rash. Spontanuous recovery. Associated C haemorrhagic fever - “Dengue shock syndrome “ Rare in India.
Histologically : Lesions in small BV C Endothelial swelling. Perivascular edema. Infiltration C MN cells.
Lab. Diagnosis : Nt & HI antibodies Prevention : Mosquito control No vaccine.
Tickborne Haemorrhagic fevers : 1. Kyasanur Forest Disease. Antigenically RSSE. Named - after the place of isolation Confined to shimoga Dt. North Karnataka Dts. - Out break - 1982. MOnkdy fever.
Vector : Haemophysalis spinigera. Reservoir, -- some extent. Transovarian. Reservoir : Forest birds & small mammar.
Bunyaviridae : Large group. Single stra. RNA. C triple - seg. Genome Transmission - Mosquitoes Sandfly. Ticks. Pathogens Nos pathogens.
5 genera : Bunyavirus - Mosquito Phlebovirus - Nairo virus - Tick. Borns Hanta, virus. Uuku virus.
Encephalitis, Fever, Aseptic menings. a. California encephalitis virus : b. La crossiac virus. Endemic in USA c. Chittoor virus - India
Vector control measures, especially mosquito control, are essential to reducing the transmission of disease by arboviruses. Habitat control involves draining swamps and removal of other pools of stagnant water (such as old tires, large outdoor potted plants, empty cans, etc.) that often serve as breeding grounds for mosquitoes. • Insecticides can be applied in rural and urban areas, inside houses and other buildings or in outdoor environments.
They are often quite effective for controlling arthropod populations, though use of some of these chemicals is controversial, and some organophosphates and organochlorides (such as DDT) have been banned in many countries. • Infertile male mosquitoes have been introduced in some areas in order to reduce the breeding rate of relevant mosquito species.
Larvicides are also used worldwide in mosquito abatement programs. • Temefos is a common mosquito larvicide.
Tent made of mosquito netting • People can also reduce the risk of getting bitten by arthropods by employing personal protective measures such as sleeping under mosquito nets, wearing protective clothing, applying insect repellents such as permethrin and DEET to clothing and exposed skin, and (where possible) avoiding areas known to harbor high arthropod populations. • Arboviral encephalitis can be prevented in two major ways: personal protective measures and public health measures to reduce the population of infected mosquitoes.
Personal measures include reducing time outdoors particularly in early evening hours, wearing long pants and long sleeved shirts and applying mosquito repellent to exposed skin areas. • Public health measures often require spraying of insecticides to kill juvenile (larvae) and adult mosquitoes
