Omsk haemorrhagic fever

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Omsk haemorrhagic fever is caused by a flavivirus transmitted mainly by Dermacentor reticulatus ticks that are associated with muskrats (Ondatra zibethicus) which are actually secondary hosts themselves[1].



Omsk haemorrhagic fever virus (OHFV), although related to other tickborne encephalitis flaviviridae, causes a rather different disease Omsk haemorrhagic fever with the neurological symptoms less prominent than haemorrhage. It is in the same group as yellow fever being an enveloped single-stranded-RNA virus with a 10787 base positive-sense genome and spherical or polygonal 40nm shape[1]. The domain III (DIII) of E protein may be a target for a vaccine[2].


The tick hosts are Dermacentor reticulatus and Dermacentor marginatus (southern and western Siberia). Omsk haemorrhagic fever virus has also been isolated from mosuitoes, gamasid mites and the taiga tick. A wide range of vertebral primary hosts are possible with natural foci being the water vole Arvicola terrestris and narrow-skulled vole Microtus gregalis. Asymptomatic carrier animals include rats, mice, hedgehogs, birds of prey and gulls.


Typically fever above 39C about 3-7 days after contact, although with some strains the viraemia can be nonspecific in up to 18%. Headache, cough, myalgia, meninigism, neuro-psychiatric, gastrointetinal upset and mucosal and skin haemorrhages may follow. The 30 to 50% who do not recover after the first two weeks have a relapse, typically with worsening haemorrhage and meninigism, and sometimes pneumonitis. Mortality is less than 2.5% but there is often prolonged dehabilitation.


  • Supportive and isolation[3]


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