ABSTRACT
Omsk hemorrhagic fever (OHF) was first recognized in the Omsk region of western Siberia, U.S.S.R., in 1944, and since 1950 there have been outbreaks in the Omsk, Novosibirsk, and Tyumen regions. Many mammalian species are involved in the maintenance and propagation of the natural tick-mediated cycle of OHF. Tick-acquired OHF also occurs in humans, but is seen mainly in agricultural workers and is more common during summer when ticks are more numerous. The cycle of Kyasanur Forest disease (KFD) virus is also markedly influenced by manmade factors. Human-to-human transmission has not been reported but laboratory-acquired infections with both viruses are common, and more than 100 cases have been recorded for KFD. KFD virus is very stable in serum and can be readily isolated by intracerebral inoculation of infant mice or in tissue culture. Vaccination against KFD is practiced in laboratory personnel in whom it has been found to be highly effective.
