Omsk hemorrhagic fever (OHF) is caused by the Omsk hemorrhagic fever virus (OHFV). OHF was first identified in 1945 in Omsk, Russia, but now occurs primarily in the western Siberia regions of Omsk, Novosibirsk, Kurgan, and Tyumen. OHF is spread through the bites of infected ticks or through direct contact with the blood or bodily fluids of an infected, sick, or dead animal, usually rodents. Symptoms of OHF begin suddenly after about 3-8 days of infection, with chills, fever, headache, severe muscle pain, vomiting, and bleeding problems. After a couple of weeks of symptoms, infected persons either recover without complications or have a second wave of symptoms that include fever and inflammation of the brain (encephalitis).