ABSTRACT
The rst epidemic outbreaks of Omsk hemorrhagic fever (OHF) were recorded in a number of rural regions of Omsk region, Russia, in 1943-1945. OHF was rstly described as a new disease in the years 1945-1946, when physicians in the northern-lake steppe and forest-steppe areas of Omsk region recorded the sporadic cases of acute febrile disease with abundant hemorrhagic signs (bleeding from the nose, mouth, uterus and skin, and hemorrhagic rash) and leukopenia (Chumakov, 1948; Mazbich and Netsky, 1952). The expedition of Russian scientists under the supervision of M. P. Chumakov took place in Omsk region with the purpose to investigate this new disease, identify its causative agent, and reveal the mode of its transmission. During this expedition, a new virus, Omsk hemorrhagic fever virus (OHFV), was isolated in 1947 from a human patient and later from Dermacentor reticulatus ticks. D. reticulatus ticks were then identied as the vector of OHFV (Chumakov, 1948; Mazich and Netsky, 1952). Later, however, a predominant pattern of contact with muskrats (Ondatra zibethicus) was seen among new cases: the illness occurred predominantly in muskrat hunters and their family members, who participated in muskrat skinning and preparing skins (Kharitonova and Leonov, 1985). Muskrats are an alien animal species in Russia that were introduced to Siberia from Canada for industrial fur production purposes (Neronov et al., 2008). Breeding of muskrats, however, did not reach its economic potential in Siberia because of fatal epizootics. It is supposed that OHFV existed silently in Siberia before muskrat’s release, but the introduction of these highly susceptible animals greatly amplied infection rates in other animals including human beings (Korsh, 1971; Ru°žek et al., 2010). In 1946-1970, 76 different epizootics of OHF were recorded in Tyumen, Kurgan, Omsk, and Novosibirsk regions, and this was followed by human cases of OHF in Omsk and Novosibirsk regions. Epizootic activity of OHFV was then recorded starting from the late 1980s in Tyumen (1987), Omsk (1988, 1999-2007), Novosibirsk (1989-present), and Kurgan (1992) regions. Between 1946 and 1958, a total of 972 human cases of OHF were ofcially recorded. In 1960-1970, the OHF incidence decreased remarkably. In the last 20 years, the disease was reported only in Novosibirsk region with the highest numbers of cases in 1990 (29 cases) and 1991 (38 cases) (Ru°žek et al., 2010, 2011).
