Type 11 Bluetongue virus was isolated in 1987 and 1988. To date, the virus has not been identified in Canada outside the Okanagan Valley. Culicoides insects can over-winter in northern climates as larvae, however the virus will not survive in the larval form. During this time the environmental temperature must remain high, or there will be insufficient viral load to produce infection in a new host. The virus may periodically move north on high winds through the United States to Canada during the warm months in infected Culicoides and infect susceptible animals in August and September when enivironmental conditions are favorable.
Cattle are the natural reservoirs of the virus.
Following infection, and an incubation period of 3 to 10 days, the virus may be present in red blood cells for 60 to 80 days, leading to a high probability that it will be bitten by Culicoides during that time. The classical form of Bluetongue is seen in sheep. Swallowing and breathing may become difficult due to swelling of the head, and there may be a nasal discharge and drooling with blood. Death may occur within 7 days of the first clinical igns. Recovering sheep may have cracking of the hooves and the muzzle skin.