EN
Fallow deer in Poland is an alien species, with an ambiguous legal status. It is considered both, a game and a farm animal, which introductions in recent years led to a substantial increase of its population. As a representative of cervids, it shares with other free-ranging and domestic ruminants many of gastrointestinal helminths, among them an alien Ashworthius sidemi, the nematode of a high pathogenicity. Until now, the parasite was observed in Poland at two foci of the wild (i.e., Bialowieża and Bieszczady forests), but not yet in fallow deer. The present study was intended to recognize the infection level, and helminth species composition, in fallow deer living in captivity. Alimentary tracts of four animals, hunted in enclosure situated in Dulowa Primeval Forest, were dissected. Nematodes belonging to seven species: Spiculopteragia spiculoptera, S. mathevossiani, S. asymmetrica, Nematodirus filicollis, Aonchotheca bovis, Oesophagostomum radiatum and Ashworthius sidemi were recovered, with the latest helminth being predominat. In the present study, the origin of A. sidemi infection, its impact on the host and abomasum nematode communities, as well as the potential parasite spread on other ruminants, were investigated.