For 300 years yellow fever was the only epidemic viral disease known to be accompanied by grave hemorrhagic manifestations. But in the 1930's cases of a devastating epidemic hemorrhagic fever were recorded for the first time among the Soviet and Japanese military personnel in the Far East. Soon outbreaks of other hemorrhagic fevers were reported from Siberia, Soviet Central Asia and also from Eastern and Northern Europe. During the past decade clinically similar diseases made their appearance in Southeast Asia and South America.
Classification of epidemic hemorrhagic fevers has become a problem because of conflicting etiologic, ecologic and geographic considerations. A convenient schema was proposed by Prof. Smorodintsev of Leningrad (Table 1). It divides the fevers into tick-borne, mosquito-borne and zoonotic categories. Two of the tick-transmitted diseases, one from Siberia and the other from Kyasanur Forest of Mysore, India, are etiologically related to Russian spring-summer encephalitis. Etiology of the other two tick-borne fevers is still unknown; presumably they are due to viruses.