FLAVIVIRUS: CLASSIFICATION AND
TAXONOMY
The flavivirus family consists of about 70 members, 13 of
which cause disease in humans. Most flaviviruses are group B arboviruses.
Flavivirus was declared a separate family in 1984. Before that
time it was closely associated to and classified along with togavirus.
Although flavivirus bears a superficial resemblance to togavirus, its
replication strategy is distinctly different from that of togavirus.
Flavivirus shares sequence homology with certain plant viruses,
particularly tobacco mosaic virus.
Flavivirus's nucleotide sequence is similar to that of the
picornavirus.
Flavivirus virions are spheroidal, enveloped, and
40-60 nm in diameter. The surface projections of the envelope may be small
(surface appears rough), or distinct (obvious fringes in negative
stains). Flavivirus's nucleocapsid is icosahedral and 25-30 nm in
diameter.
The flavivirus genome is composed of linear,
single stranded, infectious, positive sense RNA. The genome is monopartite
and 11000 nucleotides long. The structural genes are located at the 5' end
and the 5' terminus has a methylated nucleotide cap. The 3' terminus has
no poly (A) tract.
Figure 1. Schematic Representation of the Mature Flavivirus Virion.
(E - envelope protein; M - transmembrane protein; C - capsid protein)
from Henchal and Putnak (1990)