Flaviviruses

Flaviviruses

Flaviviruses were originally named as group B arboviruses. They are similar to togaviruses in that they are also single-stranded RNA viruses and have an icosahedral nucleocapsid sur-rounded by an envelope. They are slightly smaller (40–50 nm in diameter) than those of an Alphavirus, and the RNA does not have a polyadenylate sequence. The virus also lacks a con-spicuous capsid structure in the virion. All flaviviruses are serologically related, and antibodies to one virus cross-react with another virus.

The genus flavivirus contains more than 70 viruses, of which nearly 13 viruses can cause infection in humans. Most of these infections are transmitted either by mosquitoes or by ticks. However, hepatitis C virus is transmitted neither by mosqui-toes nor by ticks. The flaviviruses causing infections in humans are classified as follows:

1. Mosquito-borne flaviviruses

A.Encephalitis viruses

a)        St. Louis encephalitis virus

b)       Ilheus virus

c)        West Nile virus

d)       Murray Valley encephalitis virus

e)        Japanese encephalitis virus

B.Yellow fever virus

C.Dengue virus

2.Tick-borne flaviviruses

A.Tick-borne encephalitis viruses

a.        Russian spring-summer encephalitis virus

b.        Powassan virus       

    B.Tick-borne hemorrhagic fever viruses

a.        Kyasanur forest disease

b.        Omsk hemorrhagic fever

C. Hepatitis C virus