Kyasanur forest disease: an epidemiological view in India

Kyasanur forest disease (KFD) was first recognised as a febrile illness in the Shimoga district of Karnataka state of India. The causative agent, KFD virus (KFDV), is a highly pathogenic member in the family Flaviviridae, producing a haemorrhagic disease in infected human beings. KFD is a zoonotic disease and has so far been localised only in a southern part of India. The exact cause of its emergence in the mid 1950s is not known. A variant of KFDV, characterised serologically and genetically as Alkhurma haemorrhagic fever virus (AHFV), has been recently identified in Saudi Arabia. KFDV and AHFV share 89% sequence homology, suggesting common ancestral origin. Homology modelling of KFDV envelope (E) protein exhibited a structure similar to those of other flaviviruses, suggesting a common mechanism of virus-cell fusion. The possible mechanism of receptor-ligand interaction involved in infection by KFDV may resemble that of other flavivirses. Present understanding is that KFDV may be persisting silently in several regions of India and that antigenic and structural differences from other tick borne viruses may be related to the unique host specificity and pathogenicity of KFDV. From January 1999 through January 2005, an increasing number of KFD cases have been detected in Karnataka state of Indian subcontinent despite routine vaccination, suggesting insufficient efficacy of the current vaccine protocol. However, the exact cause of the increase of KFD cases needs further investigation. Considering the requirement of safer and more effective vaccines in general, there is clearly a need for developing an alternative vaccine as well as a rapid diagnostic system for KFD. The changing ecology of the prime focus of the KFD also warrants attention, as it may lead to establishment of the disease in newer localities, never reported before.