Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 29-30. (Budapest, 1997)

which are especially common in oak-forests and oak-forests with yoke-elms and beeches. The pine-forests of Hungary are free of ixodid ticks; however, in Dalmatia and on the Siberian taigas the major foci of infection can be found in evergreen and pine-forests as well as in juniper groves. The most important reservoirs of infection are rodents including the yellow-necked field mouse (Apodemusflavicollis), the common field mouse (Apodemus sylvaticus), the striped field mouse (Apodemus agrárius), and the common redbacked vole (Clethrionomys glareolus). Insectivorous small mammals, first of all the common mole (Talpa europaed) also have an important role in the circulation of the virus (Molnár 1983). Vertebrate animals have a complex role: (1) the pathogen multiplies in them; (2) they may act as permanent carriers of the pathogen; (3) they serve as a food source for the tick vector; and (4) they serve as a means of transport" for the ticks, i.e. play an important role in carrying the ticks from one place to another. If we place the tick onto an infected animal, the virus will appear in the tick's salivary glands within a short time (36 hours) and start to multiply there rapidly. Infected ticks may infect the attacked host, i.e. humans as the case may be, already within 6 hours (!). The virus persists in the infected ticks for a long time. From the larval stage it gets into the nymph and then into the adult tick as well. Moreover, the virus is transmitted also by the transovarian route, which means that the larvae are infected already when hatching from the eggs. Thus, the tick itself acts as a reservoir, as it stores the pathogen for many years. In view of this fact, the relatively low ratio of virus-carrier ticks is the thing to be surprised at. The national average is around 0.05%. This means that only one in every 2000 ticks harbours the virus. At the same time, sero-epidemiological investigations indicate that 3-19% of the human population living in Transdanubia and at the foot of the Alps (in Western Hungary) have been exposed to the causative agent of TBE. About 150 - 400 people receive hospital treatment for TBE in Hungary every year. The number of disease cases was especially high in the years 1982 through 1986. During the time since registration of TBE cases was started, the number of cases tended to increase at 2- to 3-year intervals, up to 1993 (Fig. 1). Since then no further increase has been observed, which can perhaps be attributed to the spread of preventive vaccination. The death toll is 1-6 patients every year. In the period between 1968 and 1995, a total of 5,561 TBE cases were diagnosed, and the mortality rate ranged between 1 and 1.5%. The mortality rate observed in Austria was higher than that (Krausler 1981). The disease occurs in natural foci, first of all in counties Zala, Somogy, Vas, Nógrád, Komárom, Veszprém, and Győr-Sopron (Tóth et al. 1996; Fig. 2). Infection may take place, although less often, also in well-kept municipal parks. (We had a patient who was absolutely certain that the tick transmitting the infection had bitten him on Margaret Island.) Half of the cases were reported from counties Zala, Somogy, Nógrád and Vas. TBE is almost unknown in the Eastern part of the country. It should not be disregarded, however, that there may be a substantial difference between the actual number of disease cases and the number of diagnosed cases. Therefore, we looked for correlations, if any, between the number of TBE suspect samples submitted to the Virological Department of the National Institute of Hygiene and the actual positivity rate of those samples. A significant correlation (p = 0.03) was found between the number of samples submitted for testing and the hit probability. Where more cases are observed, the likelihood of establishing a diagnosis will be higher, and the reverse of that thesis is also likely to be true. However, there are regions (counties Tolna, Pest, Nógrád and Heves) where a low number of tests are carried out, but their hit rate is strikingly high. It may be assumed that in these areas