Analysis of the structural protein gene sequence shows Kyasanur Forest disease virus as a distinct member in the tick-borne encephalitis virus serocomplex.

Kyasanur Forest disease (KFD) virus is a highly pathogenic member of the family Flaviviridae producing a haemorrhagic disease in infected human beings. Despite this high pathogenicity and potential epidemiological importance, there have been relatively few detailed antigenic or molecular studies on KFD virus. The nucleotide sequences of the genes encoding the structural proteins of the virus have now been determined. From these data we conclude that KFD virus is a distinct member in the tick-borne flavivirus complex with characteristic protease cleavage sites, fusion peptide, signal sequences and hydrophobic transmembrane domains. Comparison of the deduced amino acid sequences of KFD virus showed close relationships with other tick-borne flaviviruses. Among the structural proteins, the E protein showed maximum similarity (77.4% to 81.3%) to tick-borne flaviviruses. Alignment of the amino acid sequence with those of other known tick-borne flaviviruses revealed many conserved regions confirming its identity as a member of the tick-borne encephalitis group, although the genetic marker EHLPTA showed a T-->K substitution in KFD virus. The proposed genetic marker at amino acid positions 232 to 234 (AQE) was unique for KFD virus. A dendrogram derived from the amino acid alignment showed a phylogenetic relationship similar to those obtained on the basis of serological studies. The question of the sudden emergence of KFD virus in India and the possibilities of developing recombinant virus vaccines are discussed.