This paper was prepared by by Tom Solomon Lecturer in Neurology and Medical Microbiology
University of Liverpool
Tick-borne encephalitis virus circulates in small wild animals, mostly rodents,
and is transmitted by Ixodes ticks. Humans may also become infected by drinking
goat's milk.
It has a wide area of distribution across Europe and the former USSR, and its seasonal
incidence is reflected in one of the many pseudonyms 'Russian spring-summer encephalitis'.
Genetic sequencing has allowed Western tick-borne encephalitis virus, which is endemic
in Germany, Austria and much of Europe, to be distinguished from Far-Eastern tick-borne
encephalitis virus which is found across the former Soviet Union.
After one to two weeks incubation the virus causes a sudden onset of fever, headache
nausea and photophobia. In mild cases this resolves after a week, but in more severe
cases there is a second phase of illness with meningoencephalitis, or myelitis.
The latter tends to cause flaccid paralysis of the upper limb and shoulder girdle.
Respiratory muscle and bulbar (brainstem) involvement lead to respiratory failure
and death.
Far Eastern tick-borne encephalitis has a higher case fatality rate, but the Western
form is often associated with sequelae (after effects).
A formalyn inactivated vaccine given as two doses 4-6 weeks apart, has been recommended
for those likely to be exposed in the endemic forested areas of Europe and the former
USSR.
Louping ill virus is a closely related tick-borne virus notable for being the only
flavivirus found naturally in the British Isles (as well as Scandinavia). It occurs
naturally among small mammals (hares, wood-lice and shrews), but is also transmitted
to highland sheep which develop encephalitis. The disease is named after the leaping
(or louping) demonstrated by the encephalitic sheep. Very occasionally the virus
infects humans causing a meningoencephalitis, which can be severe.
Powassan virus is a distantly related tick borne flavivirus found principally among
small mammals in Canada that has occasionally caused meningoencephalitis in humans.
Tick borne encephalitis self help group –Austria
Information is in the German language
www.zecken.or.at
Last modified: March 2002