Infectious Disease Online
Pathology of Tick-borne Encephalitis
Tick-borne encephalitis is caused by tick-borne encephalitis virus, is a member of the virus genus Flavivirus , of the family Flaviviridae.
A closely related virus Russian spring-summer encephalitis virus is responsible for a similar disease with a more severe clinical course.
A number of viruses belonging to the Russian Spring Summer Encephalitis complex cause encephalitis along a wide area of the northern land mass from Scotland to Siberia.
The names given to the disease vary from one area to another depending on the variation in the prominent clinical features.
Thus in Scotland it is called ‘louping ill’ as the disease occurs primarily in sheep in which it causes a curious ‘leaping’ gait.
Human cases that result from contact with sheep are mild and present as aseptic meningitis.
It is called Central European Encephalitis, biphasic meningoencephalitis and Russian Spring Summer Encephalitis, in Central Europe, Eastern Europe and USSR respectively.
Russian spring-summer encephalitis is the most serious form, with high rates of fatality and permanent paralytic sequelae in some survivors.
Infection is transmitted by the bite of Ixodid ticks.
The virus is transmitted transovarially in ticks so that they can act as the vector as well as the reservoir host.
Wild rodents and migrating birds are other reservoirs.
Biphasic meningoencephalitis may be transmitted to man by drinking milk of infected goats.
Vertical transmission from an infected mother to fetus has occurred.
The disease is most often manifest as meningitis (inflammation of the membrane that surrounds the brain and spinal cord), encephalitis (inflammation of the brain) or meningoencephalitis (inflammation of both the brain and meninges).
The incubation period is usually between 7 and 14 days and is asymptomatic.
A characteristic biphasic febrile illness follows (lasts 2 to 4 days).
Other symptoms include fever, malaise, anorexia, muscle aches, headache and nausea or vomiting.
Involvement of central nervous system include symptoms of meningitis (Example: fever, headache, and a stiff neck) or encephalitis (Example: drowsiness, confusion, sensory disturbances or motor abnormalities such as paralysis) or meningoencephalitis.
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