Pathogenesis:
- Infection is usually of sheep with sporadic cases in cattle, deer or elk.
- Infected saliva from the tick, Ixodes ricinus, then biphasic disease.
- 1^stphase a pyrexia (>42degC or 106degF), the viraemia, the virus attached to Fc receptors.
- The animal then returns to normal and may completely recover.
- 2^ndphase involves localisation in the CNS with trembling, torticollis, irregular gait, 'louping ill'; then death or disability.
- Lesions are prevalent around the Purkinje cells of the cerebellum, in the motor nuclei of the brain stem, and the ventral horns of the spinal cord.
- In man, infection only results in influenza - like symptoms, sometimes with a coma, but recovery is expected.
- Grouse and small rodents eg shrews die from the disease.