ARBO VIRUSESARBO VIRUSES

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

SYMPTOMSSYMPTOMS

SYMPTOMS: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

LAB DIAGNOSIS

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

Venezuelan equine encephalitis Culex & Anopheles.

Wild birds - reservoirs.

Sudden onset of fever

CSF : Pleocytosis

Protein, sugar levels - Normal.

 

Febrile illness :

 

Chikungunaya :

Aedes aegypti

 

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)

 West Nile virus transmission cycle.

Haemorrhagic fevers :

 

Dengue types 1-4 -( Aedes aegypts)

Mosquito Yellow fever -

 

Kyasanur Forest disease

Tick Omsk haem. Fever - (Ixodid tick)

 

 

Both

1. 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 inapparent infe / 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

PREVENTIOPREVENTIONN

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 nettingPeople 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

TREATMENTTREATMENT

Treatment:Because the arboviral encephalitides

are viral diseases, antibiotics are not an effective form of treatment and no effective antiviral drugs have yet been discovered.

Treatment is supportive, attempting to deal with problems such as swelling of the brain, loss of the automatic breathing activity of the brain and other treatable complications like bacterial pneumonia.

Aspirin and ibuprofen should not be taken in cases of dengue fever as it could increase the risk of bleeding and cause Dengue Shock Syndrome.

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