EUROPEAN TICK BORNE ENCEPHALITIS

European tick-borne encephalitis is the most important recognized arboviral illness in Europe. Widely scattered areas have reported cases of encephalitis following tick bites. These include the east coast of Sweden, rural areas of Poland, Czechoslovakia and Central Europe including Austria, Bavaria, Hungary, and the former Soviet Republics.

Travellers to Austria are particularly concerned to read signs in airports, other public places, and pharmacies asking "Have you been vaccinated against encephalitis?" The following information is, therefore, being made available.

Agent and Epidemiology

This encephalitis is caused by group B arbovirus or flavivirus, whose family also includes the agents of yellow fever, dengue, and St. Louis encephalitis. It is similar to the Powassan virus, a sporadic cause of tick-borne encephalitis in North America. It is tick-borne, with the tick found in forested areas. The virus is excreted in milk, and can be spread via unpasteurized cow, goat or sheep milk products.

Clinical Features

The incubation period is 7-14 days. The disease has a diphasic form in 50% of the cases with a non-specific influenza-like illness lasting about a week, then a 1-3 day asymptomatic phase, followed by a central nervous system phase. There is an abrupt onset of signs of encephalitis such as tremor, dizziness and altered sensorium. Twenty percent of cases have minor neuropsychiatric sequelae and 1-5% die.

Advice to Travellers

The risk from a single tick exposure is very low and would be mainly to those travelling in wooded areas. The most practical advice is to take precautions against being bitten by ticks (e.g., wear long-sleeved clothing, no shorts or sandals, and use insect repellents). As well, unpasteurized cow, goat and sheep milk products should be avoided.

If bitten by a tick, it is prudent to consult a local physician. In Austria, immune globulin is administered for certain types of exposure. To be effective, it must be immune globulin obtained in Austria, as there would be insufficient appropriate antibodies in any North American product. There are no specific gamma globulins in Canada and the United States.

A vaccine, FSME-IMMUN®, is manufactured in Austria and should be considered for long-term travellers, but the time factor would preclude its use for short-term tourists. The recommended regime is 3 doses of vaccine, the second dose usually being given 1-3 months after the first (but this can be shortened to 2 weeks) and the third after 9-12 months. The vaccine is not approved for marketing in Canada, but is available under Health Canada's Special Access Programme (SAP). The mandate of the SAP is to provide practitioners with access to non-marketed drugs for patients facing serious or life-threatening conditions when conventional therapy has failed, is unsuitable or unavailable.

Health Canada's Special Access Program has found that the human serum albumin (HAS), used as a stabilizer in this vaccine, was prepared from plasma collected from European donors. These donors are properly screened according to European guidelines and criteria, and the FSME-IMMUN® is marketed and commonly used in Europe. However, due to the prevalence of Bovine Spongiform Encephalopathy (BSE) in European countries, there is a theoretical possibility that donors living in these countries may be silent carriers of prion agents through their exposure to BSE-infected beef products.

It is well known and recognized that, to date, the risk of transmission of vCJD by blood and blood products, is strictly theoretical, as no case of CJD or vCJD has been shown to be related to the administration of blood or blood products to a patient. The theoretical risk of vCJD to the Canadian population for vaccines manufactured with human albumin has been estimated by the Public Health Agency of Canada of Health Canada to be 1 in 100 million per treatment, per person vaccinated.

For an individual medical request, please contact the Special Access Program, Health Canada at (613) 941-2114. Further information can be obtained by contacting the distributor: Baxter Corporation, 6635 Kitimat Road, Suite 30, Mississauga, ONTARIO L5N 6J2, Telephone: 1-800-551-0478

July 23, 2002

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