The purpose of the research is studying the distribution of endoparasitoses in bison in various regions of the Russian Federation.Materials and methods. The endoparasite fauna in bison was studied in 2018–2020 in the FSBI Prioksko-Terrasny Nature Biosphere Reserve (Moscow Region), the Bison Nursery of the Siberian Branch of the Russian Academy of Sciences of the Altai Republic, the Bryansk Forest Nature Reserve (Bryansk Region), the Ugra National Park (Kaluga Region), the Vologda Region, and at the Department of Parasitology and Veterinary and Sanitary Expertise of the Moscow State Academy of Veterinary Medicine and Biotechnology – K. I. Skryabin MVA. We studied feces collected from bison of different sex and age groups near feeders in the runs, and in reserves, nurseries and in the wild. A total of 320 samples were collected and examined including 237 samples from the Prioksko-Terrasny Nature Biosphere Reserve, 15 samples from the Bison Nursery, 18 samples from the Bryansk Forest Nature Reserve, 29 samples from the Ugra National Park and 21 samples from wild bison from the Vologda Region. For helminth-coprological studies, we collected fresh feces of bison from the soil surface. The feces were examined according to generally accepted methods. The sequential washing technique was used to diagnose trematodiases, and the Kotelnikov-Khrenov and Fulleborn flotation methods were used to diagnose cestodoses, nematodoses and eimerioses.Results and discussion. The endoparasite fauna of the European bison was most diverse in the Prioksko-Terrasny Nature Biosphere Reserve, where we identified the parasitizing of two species of trematodes, one genus of cestodes, one species and four genera of nematodes and one genus of protozoa. All these pathogens parasitize both as mono- and mixed infections. One species of trematodes, one genus of nematodes and one genus of protozoa have been identified in the Ugra National Park. One genus and two genera of nematodes were found in the Bison Nursery of the Siberian Branch of the Russian Academy of Sciences of the Altai Republic and in the Bryansk Forest Nature Reserve, respectively. The dominant were gastrointestinal strongylatoses.

The epizootic and epidemiological situation of echinococcosis of wild animals, dogs and humans has been studied according to reporting data and based on our own research. It has been established that echinococcosis is widespread in the territory of the Karachay-Cherkess Republic. As a result of the autopsy of wild carnivores, it was found that the extent of echinococcosis invasion ranged from 20 to 50 % with an invasion intensity from 65,0 to 213,0 specimens/animal, in wild artiodactyls and rodents – from 14.3 to 30.0 % with AI fluctuations from 1,0 to 5,0 specimens/ animal. The average long-term incidence of echinococcosis in the population of Karachay-Cherkessia for 2000-2017, according to the Rospotrebnadzor Department for the Republic, is 4,0±0,4 (per 100 thousand population). In 2017–2018, 7 cases were registered, in 2019 – 4 cases of the disease, in 2021 – 2 cases, and in 2020 cases of echinococcosis in humans were not registered.

The species composition of helminths of the class Trematoda Rudolphi, 1808 was studied in sheep of the Karachay rough-haired breed in Kabardino-Balkaria, which is represented by 7 types of helminths: Fasciola hepatica, Dicrocoelium lanceatum, Paramphistomum cervi, P. ichikawai, Liorchis scotiae, Calicophorum calicophorum, Eurytrema pancreaticum. These species met with an extensive invasion, respectively 16,67 %, 40,00 %, 20,00 %, 16,67 %, 13,33 %, 20,00 % and 6.67 % and the intensity of the invasion from 8 to 312 copies / head.

When studying the endoparasite fauna of agricultural ruminants, it was found that the most diverse fauna of endoparasites in small cattle on the territory of the Karachay-Cherkess Republic in the sheep breeding farm LLC "Muhu", where parasitism of one species of trematodes was found: Dicrocoelium lanceatum, one species of cestodes: Moniezia benedeni, one suborder, five genera and three species of nematodes: Strongylata, Protostrongylus, Nematodirus, Bunostomum, Nematodirella, Trichocephalus, Muellerius capillaris, Dictyocaulus filaria and Strongyloides papillosus and one genus of protozoa – Eimeria. All of these pathogens parasitize both in the form of mono- and mixed invasions. In the Zolsky district of the Kabardino-Balkarian Republic, two genera and one species of trematodes were identified: Fasciola, Paramphistomum, Dicrocelium lanceatum, one suborder and two genera of nematodes: Strongylata, Trichocephalus, Protostrongylus, and one genus of protozoa, Eimeria. The dominant invasions on the territory of the North Caucasus are strongylatoses of the gastrointestinal tract.

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