Prevalence of tick-borne-encephalitis virus antibodies in Lithuania

Background: Clinical infections caused by tick-borne encephalitis virus (TBEV) are quite common in Lithuania and cause significant disease burden not only as acute cases but as chronic sequealeae as well. In order to evaluate the spread of the disease and risk factors, a population based seroprevalence study was done. Material and methods: about 1488 serum samples collected from healthy people from different parts of the country during the year 2000 were studied by hemagglutination inhibition (HI) method. For risk factor analysis detailed information was collected by a questionnaire. Results: 44 samples (2.96%) were positive. This indicates that at least 1500 infections occur in the country annually. Seropositivity did not increase with increasing age. In certain areas, seropositivity was clearly higher than the average. Other living conditions or outdoor habits correlated poorly with seropositivity. Certain groups of people such as farmers, cattle breeders, or those having a summer cottage or spending time in the nature daily had increased risk. Seropositivity was significantly linked with meningoencephalitis without laboratory confirmation for TBE in the anamnesis, and drinking of goat milk. Conclusion: The study suggests that TBEV is prevalent in Lithuania. The data also supports the view that an increase in the incidence has occurred in the 1990s. The correlation between seropositivity and presumed risk factors do not seem strong enough to warrant a selective vaccination policy based on risk factors. (C) 2002 Elsevier Science B.V. All rights reserved.