The incubation period for canine TBE in most cases is between 7 and 14 days. Clinical canine TBE is a febrile illness with multifunctional neurological manifestations such as ataxia, uncoordinated movements, abnormal reflexes, convulsions, tremor, paresis, paralysis, and cranial nerve deficits such as facial paresis. The neurobiological signs are often progressive and TBE may lead to death.
In general the risk for a tick-infected dog to develop clinical manifest TBE is very small. A serological survey performed in dogs from Sweden in 1992 proved 18 of 225 dogs (8%) to be seropositive and 16 of these 18 dogs showing neurological signs (Bjöersdorff, 2002).
The incubation period is between 3 and 28 days. The course of disease is often asymptomatic. An estimated 30% will exhibit clinical disease, mainly as a feverish flu-like disease. 10-15% of cases (increasing rate with age) will have neurological disorders with the most severe form of persisting paresis and psychiatric sequelae.
In central Europe, the typical case of encephalitis has a biphasic course, with an early, viremic, flu-like stage, followed about a week later by the appearance of signs of meningoencephalitis. CNS disease is relatively mild, but occasional severe motor dysfunction and permanent disability occur. The case fatality rate is 1% to 5%.
Russian spring-summer encephalitis (sometimes referred to as the "Far Eastern form") normally does not show a biphasic course but is characterized by massive headache, high fever, nausea, and vomiting. Delirium, coma, paralysis, and death may follow; the mortality rate is approximately 25% to 30%.
Louping ill infection is generally mild and also displays a biphasic pattern. The virus infects sheep; few cases are reported in humans.
- Bjöersdorff A: Borreliosis and tick-borne encephalitis. In: Arthropod-borne Diseases. 2002, Sci. Proc. BSAVA Congress, Birmingham, pp 185-6