Tick-borne encephalitis (TBE) is a notifiable disease in the entire region except for Denmark, and Iceland. A voluntary reporting system in Sweden has since July 2004 been replaced by mandatory reporting. Estonia, Finland, Lithuania, Norway and Sweden only report laboratory confirmed cases. Northwest Russia report both laboratory confirmed cases and cases with typical clinical picture without laboratory confirmation but with an epidemiological link to risk factors (seasonal forest visits, goat milk, etc.).
Figure 27. Number of cases of tick-borne encephalitis notified in 2003 per 100 000 population (1).
The TBE virus persists in so-called natural foci where it circulates among vertebral hosts, mainly rodents. These foci are usually stable and exist in most of the Baltic Sea region, especially the Baltic countries, land Islands, mainland Finland, Karelia and the south-eastern costal parts of Sweden. In recent years new, small foci have been identified on the Bornholm Island in Denmark and within a limited area on the southern coast of Norway.
Incidence rates may vary from year to year (figure 28). In general, an increase in incidence rates has been observed in most areas during the last decade. The highest incidence rate is usually found in Latvia, but in 2003 Lithuania experienced a record high incidence. This was probably caused by a high number of infected ticks this particular year as well as four clusters where TBE was acquired by consuming contaminated goats milk. In Lithuania, TBE affects 1.4 times as many males as females, and about 40% of cases occur in retired and unemployed people (18). One reason for this may be that these groups are more likely to collect mushrooms and berries as an additional source of income.
Figure 28. Number of cases of TBE notified per 100 000 population 1999- 2003 by groups of countries or regions (1). Denmark, Iceland, Komi, Pskov, Novgorod and Vologda regions not included.
Prevalence studies in Latvia in field-collected ticks have shown a mean annual TBE virus prevalence rate in ticks of about 3%. In 2002, the prevalence rate was 9.2% (19). In Karelia, the prevalence of TBE virus in ticks in 2001 was 9.6% (20) .Forest workers, residents and people spending long periods in endemic areas are at risk of exposure to infected ticks and contracting the disease.
Protective clothing, repellents and vaccination are the important preventive measures used in areas where TBE is endemic. Recommendations for use of the vaccine vary from country to country. TBE vaccination is not a part of the immunisation programme in any of the countries in the region, but in Latvia children in high endemic areas have been offered free TBE vaccines. Normally, the cost of vaccines has to be covered by people themselves or by their employers.