Exposure to Tick-borne Encephalitis (TBE) Virus and Borrelia burgdorferi s.l. in Agricultural Workers in Southwestern Germany

Abstract

Tick-borne pathogens represent an emerging risk for infection in many rural areas throughout the world. In Europe, the most important infectious diseases transmitted by ticks are Lyme disease and tick-borne encephalitis (TBE). Due to the ecology of the vector, some professions, e.g., rural or forestry workers, are repeatedly exposed to ticks. However, few studies have compared seropositivity in high-risk professions with that seen in the non-exposed, general population. In southwestern Germany, a seroepidemiological study was conducted to assess the seroprevalence of antibodies against these two agents in agricultural workers and to quantify the specific occupational risk by comparison with prevalence data obtained from a previous seroepidemiological survey in forestry workers and the general population. The data from standardized questionnaires and a serum sample were obtained from 316 farmers and agricultural workers. Testing for TBE antibodies was carried out with a commercial enzyme-linked immunosorbent assay (ELISA), for Borrelia burgdorferi (B. burgdorferi) antibodies by immunofluorescence test (IFT). Statistical analysis revealed that vaccinated agricultural workers and farmers came from farms with significantly more forestry work (p < 0.01) and more pastures (p < 0.05) than unvaccinated individuals. Unvaccinated individuals worked on larger vineyards than vaccinated ones (p < 0.05). Tick-bites were reported more often by vaccinated than by unvaccinated agricultural workers (p < 0.001) indicating, that the population group with the highest risk for tick exposure had been protected against TBE by vaccination. Compared to the general population, agricultural workers had a significantly increased relative risk (RR = 4.5; p < 0.05) for infection with Borrelia burgdorferi s.l., forestry workers were even more likely to get infected with this pathogen (RR = 7.6; p < 0.001) or TBEV (RR = 4.4; p < 0.05).