Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 27. (Budapest, 1994)

time, this assumption is supported also by the fact that a fairly large number of Slovakian deer were driven to the Hungarian side during the construction of the power canal of the Bős hydroelectric power plant. According to the game wardens, these animals differ from those belonging to the Szigetköz deer population in their colour and form of antlers. As in Czechoslovakia F magna infection has been known to occur at least since 1960 in several species of deer living in areas close to the Hungarian border (Kotrlá et al. 1984, Kotrly and Kotrlá 1980), the fluke is most likely to have migrated into Hungary from the North, most probably directly via the deer arriving from there. Theoretically, the fluke may have been brought to Hungarian territory not only by deer but also by the intermediate host snails carried away by flood, although in these snails it cannot survive for more than a few months. Here we mention that although in connection with a parasitological survey using questionnaires Kassai and Békési (1993) reported the occurrence of F magna in Hajdú-Bihar county, that case has not been investigated; thus, it is not known whether that observation was based on the examination of organs from an animal bagged in that region or on that of a liver derived from another area. As, according to data of the Veterinary Institute of Debrecen, the flukes found in that case were not submitted to the laboratory and nor were the circumstances of the observation documented, we could not ascertain whether this fluke actually occurred in that area. On the other hand, hunters have repeatedly seen flukes in Szigetköz deer for about three years; however, they have regarded them as common liver fluke and, thus, have not attached great importance to them. This is not surprising if we consider that in Eurasian deer F magna usually grows to a smaller size than in American deer, and it may differ from the latter also in shape. According to Kotrlá and Kotrly (1980) this phenomenon, occurring in a non-indigenous host and in a new habitat, may sometimes render accurate species identification more difficult. By now the fluke seems to have grown to such high numbers that, according to the game wardens, the decisive majority of bagged deer carry it. The high prevalence of F magna infection is indicated also by the high ratio of egg-containing droppings. The presence of roughly even-aged flukes found in the liver of the deer examined by us indicates that until its bagging the given animal had been infected by flukes on a single occasion only. Considering this, the intensity of its infection seems to be very high, as even the parasite's natural host, the white-tailed deer (Odocoileus virginianus) living in its original habitat usually harbours not more than five flukes (Foreyt et al. 1977). The pairing tendency observed also by us, i.e. the occurrence of flukes in pairs in a cavity formed around them, was demonstrated also in white-tailed deer (Foreyt et al. 1977). From the point of view of adaptation, the advantage of pairing may be the facilitation of mutual fertilization. F magna infection of the deer population living in the Szigetköz region has dual importance. On the one hand, it poses the risk of further spread of infection in the game population. Eggs may overwinter in the outworld (Erhardová 1965) and may be carried away by water to distant places. The Lymnaea species acting as intermediate hosts are very common in that faunal region. This is especially true for Lymnaea truncatula, which is the most suitable intermediate host for the development of F