This is a viral disease affecting sheep, grouse, hares, deer, elk, small rodents, ticks and humans; therefore the disease is zoonotic. The reservoir host for this disease is hard ticks (Ixodes ricinus) and this is transmitted to the host by saliva when the tick bites. Therefore, spread mirrors seasonal tick activity.
The virus replicates in macrophages causing pyrexia and then recovery. The second phase of the virus replication occurs in Purkinje cells of the cerebellum and motor nuclei of the brain stem.
Signs in sheep include trembling, torticollis, and irregular gait. In grouse, the disease causes them to die of starvation. In humans, signs are flu-like and can be followed by a coma and rarely death. Usually however, recovery is normal.
Diagnosis is by presence of clinical signs, plus knowledge of tick season. Definitive diagnosis can be achieved by virus isolation and histopathology of brain tissue.
This can be achieved by dipping sheep in acaracides to control the vector, the tick. Inactivated vaccines in late pregnancy can be used to boost maternal antibody. Lambs are usually inoculated when over 4 months of age. A vaccine is available in humans for those at risk of the disease.
Bridger, J and Russell, P (2007) Virology Study Book, Royal Veterinary College
Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses Elsevier Health Sciences
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