[Tick-borne encephalitis transmitted by raw milk--what is the significance of this route of infection? Studies in the epidemic region of South-West Germany].

Despite the observation of TBE cases after consumption of raw milk from cows or goats, so far the proof of the alimentary route of human infection has not been possible. In the regions of southwestern Germany, where TBE is known to be endemic, milk-borne TBE infections have not yet been observed. To assess the significance of raw milk consumption for viral transmission, a cross-sectional study (114 forestry workers, 177 individuals exposed during their leisure-time activities, 170 non-exposed individuals) and a case-control study (50 TBE patients, 150 controls) were carried out. The results of the study show that both the time spent in the endemic region and also the professional exposure to ticks do influence TBE seroprevalence, whereas the consumption of raw milk (milk directly from the farmer) is no major risk factor for TBE infection or disease. Among leisure-time activities, only hunting has an effect comparable to the one of the professional exposure to ticks. Besides epidemiological data obtained in humans, serological investigations of cows were performed. Here it is shown that milk-producing animals are involved in the natural transmission of TBE virus. Since former studies had shown that TBE-viremic animals excrete the virus with the milk--although over a short period and in low concentrations--the occurrence of milk-borne TBE infections cannot be excluded in the endemic regions of south-western Germany. However, from the epidemiological point of view, their significance may be neglected. Vaccination has proven the most reliable means of TBE prevention, irrespective of the route of infection.