Omsk hemorrhagic fever virus (OHFV) is an enveloped, single‑stranded RNA virus in the genus Flavivirus and the agent of Omsk hemorrhagic fever, a tick‑borne zoonotic disease in western Siberia. The virus has a genome of about 11 kilobases, encoding a single polyprotein that is cleaved into structural proteins—capsid, precursor membrane and envelope—and nonstructural proteins that form the replicase complex. Virions are roughly 50 nanometres in diameter, with a lipid envelope studded with glycosylated E proteins that mediate host cell entry.
Genome and Virology
OHFV is closely related to tick-borne encephalitis virus but forms a distinct species within the tick-borne flavivirus group. The genomic RNA contains a 5′ cap and lacks a poly(A) tail. After a tick bite or exposure to infected animal tissues, the virus enters cells by clathrin-mediated endocytosis; low pH in the endosome triggers conformational rearrangement of the envelope protein, resulting in membrane fusion and release of the nucleocapsid. The polyprotein is translated at the rough endoplasmic reticulum and processed by host signal peptidases and the viral NS3 serine protease to generate functional proteins. Replication complexes form in virus-induced membrane invaginations, where the NS5 polymerase synthesises a negative-sense intermediate and nascent genomes. Virion assembly occurs at the endoplasmic reticulum; prM cleavage during egress yields mature infectious particles. OHFV replicates in macrophages, endothelial cells and hepatocytes, contributing to systemic infection and haemorrhagic manifestations.
Outbreaks and Key Facts
Omsk hemorrhagic fever was first recognised during muskrat trapping campaigns in the Omsk and Tyumen regions of Russia in the late 1940s. The virus is maintained in a natural cycle involving Dermacentor reticulatus ticks and small mammals, especially muskrats and water voles. Humans become infected through tick bites or contact with blood and tissues of infected animals; ingestion of contaminated water has also been implicated. Outbreaks have been sporadic, with several hundred cases reported between 1945 and 1958 and occasional cases since. The disease has an incubation period of 3–9 days and presents with sudden fever, headache, myalgia and haemorrhagic manifestations such as petechiae and gastrointestinal bleeding; case fatality is about 1–2%. There is no specific antiviral therapy; care is supportive, focusing on fluid management and treatment of complications. Prevention relies on avoiding tick-infested areas, using protective clothing and repellents, and controlling muskrat populations.
Omsk hemorrhagic fever virus serves as a reminder of the diversity of tick-borne flaviviruses and their capacity to cause severe haemorrhagic illness.
Related Terms: Tick-borne encephalitis virus, Kyasanur forest disease virus, Powassan virus, Flavivirus, Hemorrhagic fever