ARBO VIRUSES - Similima

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ARBO VIRUSES - Similima

ARBO VIRUSES

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ARBO – Define viruses transmitted by

arthropod vectors

WHO definition of Arbo viruses-

� Viruses maintained in nature through

biological transmission in susceptible

vertebrate hosts.

� By haematophagous arthropods.

� Trans-ovarian/ venereal transmission.

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CLASSIFICATION

>500 Arbo viruses

Five families

� Toga viridae

� Flavi ”

� Bunya ”

� Rhabdo ”

� Reo ”

� In India over 40, of these, >10 found to

produce human disease.

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NAMING

� According to disease - Yellow fever

� Place of isolation –Kaysanur Forest Disease

� Local name of the disease – Chikungunya.

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PROPERTIES OF ARBO VIRUSES

� Ability to multiply in arthropods

� All induce fatal encephalitis in suckling mice

� Most multiply in mammalian tissue culture

systems at 37°C

� Dengue & Ross river virus multiply in Aedes

mosquito cells

� Mosquito borne Arbo viruses are not

transmitted by ticks & vice versa

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PATHOGENESIS

Virus entry- through bite of insect vector

Primary replication in RE System cells

�Lymph nodes

�Liver

�Spleen

�Endothelial cells of blood vessels

Primary viremia →flu like symptoms

Virus transported to target sites

Target sites - CNS, Skin, Liver

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CLINICAL FEATURES

� Encephalitis 7-10 days after infection

Fever ,headache, neck stiffness

Nausea, vomiting,

Drowsiness, disorientation

Stupor/ coma

� Fever with/ without rash

� Fever & Arthralgia

� Haemarragic fevers

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• Isolation of virus

� CSF

DIAGNOSIS

� Brain biopsy specimen

I/C inoculation in suckling mice

• Isolates identified by

� Haemagglutination

� HI

� Immunofluorescence

� Nuetralisation with antiserum

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Lab. Diagnosis contd….

� Arbovirus specific RNA detection

� Serology

� Serotype specific IgM antibody

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Treatment

� No specific anti arboviral agent

� Supportive measures

� Anticonvulsants

� Antipyretics

� IV infusions

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Some Important

Arbo Viral Infections

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JAPANESE ENCEPHALITIS

� Recognised first in Japan- 1871

� In India – 1955, districts of Tamil Nadu

� Diagnosed serologically

� JE virus isolated from mosquitoes

� Isolations from man -1958

� Till 1972 epidemics only in T. Nadu

� Now a major public health problem

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NATURAL CYCLE OF JE VIRUS

� Principal vector

Culex tritaeniorhyncus

Culex vishnui

Culex pseudovishnui

� Natural infection- Ardeid birds

Herons are reservoir hosts

Pigs – amplifier hosts

Human infection is a dead end

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NATURAL CYCLE-JE VIRUS Contd…

� Birds like ducks, pigeons &

sparrows also involved

� Vertebrate hosts are pigs, cattle &

buffalo

� High cattle pig ratio limits human

infection

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CLINICAL PICTURE

• Prodromal stage - 1-6 days

� Fever, headache,vomiting

• Acute encephalitic stage

� Continuing fever

� CNS symptoms

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CLINICAL PICTURE contd…

� Late stage

� Recovery

� Irreversible neuron injury

� Majority asymptomatic

� 500-1000 inapparent infections occur per

clinical disease.

� Mortality 50%

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YELLOW FEVER

� Native of Africa - ‘YELLOW JACK’

� Vector is Aedes aegypti

� Two cycles exist

Urban cycle

Sylvatic cycle

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CLINICAL PICTURE IN YF

� Viraemic phase

� Typical haemorrhagic fever

� Intoxication phase

� Prominent hepatic necrosis

� Jaundice, black vomit, anuria & terminal

delirium

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Histology of liver

DIAGNOSIS

� Cloudy & fatty degeneration

� Typical mid zonal necrosis

� Necrosed cells Coalesce Hyalinise

� Form eosinophilic masses

� ‘Councilman bodies’

� I/N inclusions – ‘Torres bodies’

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CONTROL MEASURES

� Control of vector

� Two effective vaccines

Dakar vaccine- neurotropic

17 D vaccine- chick embryo

� Mandatory for travel to & from endemic

areas. Immunity for 10 yrs

� India is highly receptive for yellow fever

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DENGUE FEVER

� Most imp. & Common vector borne disease

� Most widely distributed of all viruses

� Four types of virus

� Den 1 - Hawai in 1944

� Den 2 - New Guinea in 1944

� Den 3 & 4 - Philippines in 1956

� In India all four types exist

� More than one virus isolated from same patient

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EPIDEMIOLOGY

� Vector is AEDES MOSQUITOES

� Transmission person to person

� Human beings are the only hosts

� I.P 2-8 days

� Classical Dengue Fever common in

older children and adult

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CLINICAL FEATURES

Classical Dengue Fever

� Fever - sudden onset& biphasic

� Headache

� Retrobulbar pain

� Conjuunctival injection

� Pain in the back & limbs

‘Break bone fever’

� Lymphadenopathy

� Maculopapular rash

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DHF/ DSS

� Mostly confined among children (5-10 yrs)

� Where multiple Dengue virus exist

� Hyperimmune response

In patients previously infected with

Dengue virus, re-infection with a

different serotype

� Antibodies formed against first virus forms

immune complexes

� Due to enhanced immunological response

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CLINICAL FEATURES of DHF/ DSS

� Initially symptoms of Dengue fever

� Haemmorragic rash

� Thrombocytopenia

� Shock

� Epidemics of DHF/DSS seen in

Thailand, S.E Asia and India

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LAB DIAGNOSIS

� Virus found in serum, blood and other

tissues for 2-7 days of fever

� Isolation difficult.

� Inoculation into the thorax of mosquitoes

‘Toxorhynchitis’- large size

� Inoculation into mosquito cell lines

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IF- Showing infected mosquito cells

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Diagnosis contd…..

� Antigen detection by ELISA or

immunohistochemistry

� Dengue RNA – Reverse PCR

� Serology

� IgM capture ELISA

� HI

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PROPHYLAXIS

� No effective vaccine

� Live attenuated vaccine containing all four

serotypes under clinical trial

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KYASANUR FOREST DISEASE

� An Indian haemmarrhagic disease

� Occurred in Kyasanur forest in Shimoga

district, Karnataka in 1957

� Dead monkeys & associated febrile

illness

in some villagers

� New arbo virus isolated from patients &

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monkeys: by NIV, Pune.

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CLINICAL FEATURES

� Sudden onset of fever, headache, myalgia

conjunctivitis, haemorrages into skin

mucosa & viscera.

� Outbreaks initially confined to Shimoga

� Later spread to other places

� Outbreaks known as ‘Monkey Fever’

� Ticks are the vectors

� Associated with deforestation.

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EPIDEMIOLOGY

� 34 species of ticks recovered from KFD area

� Chief vector Haemophysalis spinigera

� Contributes to > 90 % of isolations

� Man is only tangentially infected dead end

� Disease is seasonal, between December & June

� Peak in February & May

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CLASSIFICATION OF ARBOVIRUSES

Fever with or without rash

� Chikungunya

� O’nyong O’nyong

� Ross fever vector

� Dengue moquito

� West nile

� Rift valley fever

� Sandfly fever sandfly www.similima.com

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Encephalitis viruses

� Eastern Equine Encephalitis

� Western Equine Encephalitis

� Venezuelan Equine Encephalitis

� St. Louis Encephalitis Mosquito

� West Nile

� Japanese Encephalitis

� Murray Valley Encephalitis

� Russian Spring Summer Encephalitis Tick

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HEMORRHAGIC FEVER

� Chikungunya

� Dengue, types 1- 4 Mosquito

� Yellow fever

� Kyasanur Forest Disease

� Omsk hemorrhagic fever Ticks

� Crimean-Congo hemorrhagic fever

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THANK YOU

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