Omsk hemorrhagic fever is an encephalitis of the Flaviviridae family endemic to Russia, specifically the Omsk region and other areas of western Siberia. It is related to yellow fever and Kyasanur forest disease. Tick-borne transmission occurs with exposure to a carrier species (Dermacentor reticulatus, Dermacentor marginatus, Ixodes persulcatus [taiga tick]), but illness may also be contracted via infected water voles and muskrats. Workers handling live animals or animal pelts are at significant risk, as most cases occur in muskrat trappers. Infection confers immunity. The mortality rate of Omsk hemorrhagic fever is 10%.

Incubation is typically 2-9 days. Initial presentation includes sudden onset of flu-like symptoms with fever, chills, headache, myalgia, arthralgia, and severe prostration. Other hallmarks are flushing of the upper body, conjunctival redness, vesicles on the soft palate, petechiae, cervical lymphadenopathy, and bradycardia. Within 2 weeks, pneumonia, CNS involvement (delirium, seizures, coma), or GI and mucosal bleeding may ensue.

Thrombocytopenia, increased LFTs, and leukopenia may be observed.

Person-to-person transmission has not been documented, but contraction via exposure to infected body fluids has been documented. A vaccine (inactivated TBE) is available only in Russia.