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Arboviruses Dr. Ashish J PG Dept of Microbiology

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Arthropod-borne viruses ( arboviruses ) are viruses that can be transmitted to man by arthropod vectors. The WHO definition is as follows “Viruses  maintained  in nature principally, or to an important extent,  through  biological  transmission  between   susceptible vertebrate  hosts by haematophagus arthropods or through transovarian and possibly venereal transmission in arthropods. ”

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Examples of Arthropod Vectors Aedes Aegyti Assorted Ticks Phlebotmine Sandfly Culex Mosquito

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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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Transmission Cycles Man - arthropod -man e.g. dengue, urban yellow fever. Animal - arthropod vector - man e.g. Japanese encephalitis, EEE, WEE, jungle yellow fever. Both cycles may be seen with some arboviruses such as yellow fever.

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Family and Genus Virus causing Encephalitis Febrile Illness Hemorrhagic fever Togaviridae Alphavirus Western Equine Chikungunya Chikungunya Eastern Equine Onyang Onyang Venezualean Equine Semiliki forest Ross River Semlit

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Flaviviridae Flavivirus St. Louis Dengue 1-4 Dengue West Nile Yellow fever Mosquito borne Japanese B Murray Valley Tick borne Russina spring summer KFD Powassan Omsk Hemorrhagic fever

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Bunyaviridae Bunyavirus California Chittor virus La Cross Phlebovirus Sandfly fever Rift Valley fever Nairovirus Nairobi sheep Ganjam virus Hantavirus Hantaan virus Pumala Sin Nombre

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Reoviridae Orbivirus African horse sickness Colorado tick born virus Rhabdoviridae Stomatitis Vesiculor Chandipura Arenaviridae Junin Machupo Gunarito Sabia Lassa Lymphocytic choriomeningitis

Arboviruses in India:

Arboviruses in India Togaviridae Alphavirus Chikungunya Semlki forest Flaviviridae Flavi virus Japanese B Encephalitis West Nile Virus Dengue 1-4 KFD Bunyaviridae Phlebovirus Sandfly fever Nairovirus Ganjam Reoviridae Orbivirus African Horse serum sickness Rhabdoviridae Chandipura virus Ungrouped Wanowri virus, Chittor virus


Flavivirus 25-30nm, 11-12 kbp in length ssRNA , + ive sense Enveloped, 2 glycoproteins . 3 structural protein & 7 non structural protein

Japanese B encephalitis:

Japanese B encephalitis “ Acute viral encephalitis caused by ss + ive sense RNA belong to family Flaviviridae ”. Majority of cases are asymptomatic

Japanese B Encephalitis :

Japanese B Encephalitis


History Virus suppoded to have originated from its ancestral virus in mid 1500’s. Japan 1 st time mention 1870’s. Epidemic in 1924 with case fatality of 62% Isolated from case in 1935 Isolated from vector 1938 India-1955, CMC, Vellore 1973 Bengal and Bihar epidemic. Karnataka- Bellary, Kolar


Pathogenesis Transmission: Zoonotic disease. Reservoir host- Herons Amplifier host- Pigs. Vectors are- Culex tritaeniorhyncus Culex vishnui Culex pseudovishnui

Transmission cycle:

Transmission cycle

Culex tritaeniorhynchus Culex tritaeniorhynchus :

Culex tritaeniorhynchus Culex tritaeniorhynchus


Pathogenesis Infected arthoropod bite Virus injected into blood Localized in RES. Multiplication in RES Viremia Entry into CNS Direct and Indirect effect


Pathology JBV infected brain shows Gross edema ( cause of death ) Perivascular inflammation- Endothelial cells of capillaries Lytic lesions in Thalamus, Basal ganglia and Substantia nigra

Clinical features:

Clinical features

Clinical features:

Clinical features Incubation period- 10-14 days 3 patterns Children between 5-15 years and elderly In endemic areas any child with increased fever, seizures and altered sensorium is diagnosed as Japapnese B encephalitis 3 stages

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Lethargy Sudden fever Vomiting and diarrhea Tremors or convulsions Headache Change in consciousness Irritability or restlessness Common symptoms of encephalitis

1. Prodromal stage:

1. Prodromal stage Flu like symptoms Quick onset Fever Headaches Rigor Malaise Nausea Vomiting Normally this last around 1-6 days

2. Acute stage:

2. Acute stage Post 6 th day associated with Drowsiness Stupor Mental confusion Convulsions Mask like face Abnormal movements Speech impairment. Coma

3. Late stage:

3. Late stage Extra pyrimidal symptoms Post encephalitis Parkinsonis

Complications :

Complications Status Epilepticus Mental retardation Increased deep tendon reflexes.

Differential Diagnosis:

Differential Diagnosis Febrile convulsions Viral encephalitis Reye’s syndrome Cerebral malaria


Diagnosis Lumbar puncture not done Diagnosis done by CT and MRI CT- Gross edema and hypodense regions MRI- Hyper intense lesions. Cell count not specific. Pleocytosis with increased protein

Lab Diagnosis:

Lab Diagnosis Lab diagnosis needed for confirmation and eradication. Specimen- CSF, Brain, and serum

Virus Isolation:

Virus Isolation Mammalian tissue cultures- Vero/BHK cells, MRC 5, and Mosquito cell line C6/36. Preferred is mosquito cell Appearance of plaques important.


Serology Haemagglutionation inhibition or ELISA on paired sear. Evidence of onset MAC ELISA-80% after 3-4 days of infection.

Detection of Viral Antigen:

Detection of Viral Antigen Cultured on mosquito cell lines or mosquito throat incubated at 28 o c for 10 days. Acute phase blood innoculation at 30 0 c for 14 days.

Detection of RNA:

Detection of RNA Viral RNA extracted from serum or tissue culture cells or mosquito homogenates using guanidine isothiocyanate mixture. PCR performed.

Animal inoculation:

Animal inoculation Intracerebral inoculation into suckling mice aged <48 hours. Examine daily for sign of encephalitis. Brains from moribund mice are removed. Serogrouping done by heamagglutination inhibition.


Prophylaxis No drugs 1930- Mouse brain derived vaccine developed. 1987- India.

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3 types of vaccine being used now Mouse brain derived, purified and inactivated. Cell culutre derived inactivated vaccine. Cell culture derived live attenuated vaccine. Vaccine in pipline Inactivated vero cell derived Beijeing 1 Inactivated vero cell SA Live attenuated chimeric vaccine.

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39 Prevention Personal protective measures and mosquito elimination are the most important travellers going to endemic areas may consider vaccination

Strategy in India:

Strategy in India Comes under National Vector Borne disease control programme . Measures tried Attack mosquitoes Ecology corrected Vaccination of pigs Vaccination of people


Dengue “ Acute febrile illness with possibilities of complication caused by ssRNA + ive sense virus belonging to family Flaviviridae ”

Dengue Virus:

Dengue Virus Electron Micrograms


History Ka-Dingo pepo from Swahili Dengue in spanish . 1 st recoganized epidemic occurred simultaneously in Asia, Africa, and North America. Break bone fever -1789 Viral etiology and transmission- 20 th century World war II major cause of spread. India 1812 1 st recorded case. Right now burden of disease in Asia, Africa 1998 Pandemic 1.2 million people

Dengue on the Globe:

Dengue on the Globe Highly endemic Recently acquired


Introduction Self limited Dengue fever Life threatening syndrome called Dengue Hemorrhagic syndrome and Dengue shock syndrome 4 subtypes DenV1- Isolated in Hawai DenV2- New Guinea 1944 DenV3-4- Philippines 1956 Genetic variation within serotypes

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The most common epidemic vector of dengue in the world is the Aedes aegypti mosquito. It can be identified by the white bands or scale patterns on its legs and thorax.

Dengue Transmission Cycle:

Dengue Transmission Cycle

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2 cycles of transmission Forest/Sylvan Urban cycle Aedes aegypticus and A. albopictus Bite soon after day break. More prone for explosive epidemics


Immunity Type specific and possible for person to have 4 separate episodes of dengue fever. Infection confers life long immunity Re infection with diff serotype Dengue hemorrhagic fever. 3 theories

Initial Immunogenecity:

Initial Immunogenecity

Immune Complexes:

Immune Complexes

Attack on Host Immune Cells:

Attack on Host Immune Cells

Clinical Picture:

Clinical Picture Incubation period 3-14 days 4 days after infection febrile. Headache, malaise, chills. Back and joint pain. Characteristic retro bulbar pain Nausea and Vomiting. Rash appear 3-4 days, bright red petechiae and usually appear in lower limb and chest. Lymph nodes enlarged. Saddle back fever

Dengue Hemorrhagic Fever:

Dengue Hemorrhagic Fever Dengue fever plus Sudden rise in Temp with facial flush Convulsions Increased bleeding Frequent vomiting.



Ecchymosis – Periorbital Edema:

Ecchymosis – Periorbital Edema

Dengue Shock Syndrome:

Dengue Shock Syndrome Classical presentation Weak rapid pulse Cold clammy skin Narrow pulse pressure Altered mental status Petechial Hemorrhage. Ecchymosis Minor injury cause bleeding



Unusual Presentation:

Unusual Presentation Encephalopathy Hepatic Damage Cardiomyopathy Severe GI Bleeding

Differential Diagnosis:

Differential Diagnosis FM complex Anicteric leptospirosis Rickettsial fevers Influenza, Measles, Rubella DHF / DSS Other hemorrhagic fevers DIC due to septicemia Complicated Malaria


Diagnoses Ususally clinical Total WBC- Leucopenia with leucocytosis and neutrphilia Thrombocytopenia Increased SGOT and SGPT

Lab Diagnosis:

Lab Diagnosis 1 . Rapid Detection Reverse transcriptase PCR. Rapid detection and serotyping in acute phase serum 2. Isolation of virus Deffeicult Mosquito cell line C6/36. Intrathoracic inoculation in larvae of Toxorynchites

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3 . Serology Hemagglutination inhibition antibody 4 days after onset Rapid assay done while detection of NS1, IgM and IgG . Neutralization test also important method for detection MAC-ELISA of choice.

Immuno Detection Tests:

Immuno Detection Tests ELISA Plate IgM-capture ELISA


Treatment No antiviral Supportive therapy Avoid Aspirin DHF with fluid replacement therapy, O2, Platelet transfusion. No effective vaccine cause protection against 4 types needed. Several Candidate vaccine on trial

Vector Control of Dengue:

Vector Control of Dengue Mosquito control is expensive –impossible Destruction of breeding sites – viable Spraying insecticides for adult control- ? Individual measures to avoid vector contact Mosquito screens, repellents (DEET) Permithrin impregnated clothing


References Jawetz textbook of Microbiology Bailey and Scot textbook of Microbiology Ananthnarayan textbook of Microbiology. Dengue: guidelines for diagnosis, treatment, prevention and control. Second edition. Geneva: World Health Organization. 2009. Accessed at Tom Soloman ‘New vaccine for Japanese encephalitis’ the Lancet 2008 Center for Diseases Control, Atlanta National Institute of Communicable Diseases, New Delhi Harrison's Principles of Internal Medicine, 15 ed

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