Promising medicinal plants for treatment of helminths of bison.

Bison bonasus (Linnaeus, 1758) and B. bison (Linnaeus, 1758) are mammals placed in the Red Book of the International Union for Conservation of Nature. Populations of those species of animals are under threat of extinction. Therefore, developing practical measures for their protection is of great significance. However, one way of improving the population of bisons is integrated control of their helminths. The article generalizes the data about the helminth fauna of B. bonasus and B. bison, as well as data on relatively medicinal plants with anthelmintic properties. The results of the analysis indicate the existence of more effective medicinal plants that could be used to develop novel anthelmintic drugs. Less effective anthelmintic plants may be consumed by animals in pastures or with hay in the conditions of stable maintenance. Helminths in bison populations should be controlled using plant-based anthelmintic drugs taking into account infections in animals in particular herds of bisons by more or less dangerous helminths.

Identification and characterization of Eimeria spp. in western north American Bison (Bison bison) herds and potential risk of cross-species transmission.

The American bison (Bison bison) is an iconic native wildlife species of the Great Plains of North America. Recently, farmed bison have also gained importance to the livestock industry across the United States and Canada. One of the common diseases in young bison is coccidiosis, a diarrheal disease caused by protozoa that can result in significant morbidity. The goal of the present study was to investigate occurrence and identity of bison coccidia of the genus Eimeria in both farmed and free-ranging bison with focus on potential Eimeria species transmissibility between bison and cattle. Individual bison (up to one year of age) were sampled across Wyoming, Colorado, Nebraska, and South Dakota on six bison ranches (n = 137) and in two free-range herds (n = 70). Eimeria populations were assessed by fecal analyses. Morphological identification revealed presence of oocysts consistent with Eimeria (E.) bovis, E. zuernii, E. ellipsoidalis, E. cylindrica, E. alabamensis, E. auburnensis, E. canadensis, E. pellita, E. subspherica, and E. bukidnonensis, all of which are described in cattle. Additional Eimeria species specific ITS1 sequencing data along with generated phylogenetic maximum likelihood trees suggest that Eimeria species from cattle, namely E. bovis, E. zuernii, E. alabamensis, E. cylindrica, E. brasiliensis, E. ellipsoidalis, and E. wyomingensis, are genetically consistent with the detected bison coccidia. In conclusion, the study results indicate that bison harbor a variety of Eimeria species and bison Eimeria species appear to be transmissible between different bovine species such as bison and cattle.

Pathogens with potential impact on reproduction in captive and free-ranging European bison (Bison bonasus) in Poland - a serological survey.

BACKGROUND: The European bison is an endangered species, and as such it is extremely important to monitor herds for pathogens which can lead to reproductive failure. The aim of the present study was to determine the current prevalence of antibodies to pathogens known to potentially influence reproduction in European bison. Serum samples from 183 bison, originating from different parts of Poland, were tested using commercial ELISA tests for antibodies to Chlamydia spp., Coxiella burnetti, Leptospira interrogans, Neospora caninum and Toxoplasma gondii; the findings were compared between captive and main free-ranging herds, and with regard to the influence of demographic factors such as age and sex. The prevalence of seropositivity was also checked with regard to location and the animal species sharing it. RESULTS: Chlamydia spp. antibodies were present in 48 out of 130 (36.9%) tested samples. Coxiella burnetii was found in one sample out of 178 (0.58%). N. caninum in 36 out of 172 (20.9%) and T. gondii in 23 out of 172 (13.4%). No sample was positive for leptospirosis. Neither sex nor age appeared to have a significant effect on the occurrence of antibodies to the identified species. The prevalence of Chlamydia spp. in the samples varied significantly according to location; however, similar frequency ranges were observed between free ranging and captive herds. In contrast, antibodies to N. caninum were more common in free-ranging herds than captive herds, with the highest frequency observed in the Bieszczady Mountains. CONCLUSIONS: Chlamydia spp., N. caninum and T. gondii might have a similar impact on the reproductive potential of European bison as they have on cattle. The high occurrence of antibodies to N. caninum in bison from the Bieszczady Mountains may be associated with the relatively high density of the wolf population in the area.

Toxocara vitulorum infection in European bison (Bison bonasus) calves from Central Germany.

Whitish roundworms were found in the faeces of a female (3 months old) and a male (1 month old) European bison calf from an animal park in Central Germany. Since the faeces samples were not assignable to the individual animals, it is not certain if both calves were infected. The worms were identified as Toxocara vitulorum by morphological and molecular analysis, and a treatment with doramectin was initiated. To monitor the success of the therapy, faecal samples were examined before and after treatment by combined flotation/sedimentation technique, followed by a quantitative McMaster analysis in case of positive results. Additionally, stages of several Eimeria species and Trichuris sp. were found. Eggs of T. vitulorum were detected one week after application of doramectin, so, a second treatment was performed. However, no eggs of T. vitulorum were found at the time of the second treatment. Because of the difficulty of T. vitulorum eradication in infected herds, further investigations in the following year will be conducted.

Occurrence of tapeworms Moniezia benedeni (Moniez, 1879) in European bison Bison bonasus L. in Bialowieza Primeval Forest

Tapeworms Moniezia benedeni are cosmopolitan parasites of wild and domestic ruminants. The aim of this study was to examine the prevalence of those tapeworms in European bison in Bialowieza Primeval Forest. Parasitological necropsy of small intestine of 26 bison, aged from 3 months to 26 years was performed in years 2007­2011. Tapeworms M. benedeni were isolated from 11 examined animals and the prevalence of infection was estimated on 42.3%. Intensity of infection was ranging from 2 to 25 tapeworms and the mean intensity was estimated on 5.8 specimens. Prevalence in the group of calves reached 50% and in adult bison ­ 33.3%. Intensity of infection in calves was estimated on 2 to 5 tapeworms while in adult animals it was ranging from 1 to 2 parasites. High prevalence of tapeworms M. benedeni in European bison might result from poor condition or weak immunity of eliminated animals.

A morphological and molecular comparison of Eimeria bovis-like oocysts (Apicomplexa: Eimeriidae) from European bison, Bison bonasus L., and cattle, Bos taurus L., and the development of two multiplex PCR assays for their identification.

The European bison, Bison bonasus is the largest terrestrial mammal in Europe; it is also on the red list, being recognized as vulnerable to extinction by the International Union for Conservation of Nature. The species suffers from low genetic variability, rendering it vulnerable to various environmental and biological threats. This study presents the first molecular confirmation of Eimeria bovis infection in European bison, and details a 1708 bp nucleotide sequence of the 18S rRNA gene in European bison-derived E. bovis (GenBank: MK691697). It also describes two multiplex PCR assays based on 18S rRNA gene for identifying Eimeria bovis oocysts and developmental stages in European bison and cattle. These yielded DNA banding patterns common for those of Eimeria spp. (250 bp for the first assay and 305 bp for the second assay) and species-specific E. bovis DNA in positive samples (344 bp and 586 bp, respectively). Both multiplex PCRs yielded bands characteristic of Eimeria spp. and E. bovis in samples containing DNA of oocysts from both bison and cattle. Moreover, convergent results were obtained for the DNA of the wall of colon in both assays, indicating the presence of developmental stages of Eimeria spp. other than E. bovis. Despite displaying the same sporulation time (four days), and similar general morphological features, the E. bovis oocysts derived from European bison were significantly narrower than those obtained from cattle (t = -6.19, p < 0.001), with a significantly higher shape index (length/width ratio) (t = 3.94, p <  0.001). The result provides further evidence for infection of European bison with a highly-pathogenic bovine protozoan, E. bovis.

High species diversity of trichostrongyle parasite communities within and between Western Canadian commercial and conservation bison herds revealed by nemabiome metabarcoding.

BACKGROUND: Many trichostrongylid nematode species are reported to infect bison, some of which are major causes of disase and production loss in North American bison herds. However, there is little information on the species distribution and relative abundance of these parasites in either commercial or conservation herds. This is largely because trichostrongylid nematode species cannot be distinguished by visual microscopic examination of eggs present in feces. Consequently, we have applied ITS2 rDNA nemabiome metabarcoding to describe the trichostrongyle parasite species diversity in 58 bison production groups derived from 38 commercial North American plains bison (Bison bison bison) herds from across western Canada, and two bison conservation herds located in Elk Island National Park (EINP) [plains bison and wood bison (Bison bison athabascae)] and one in Grasslands National Park (GNP) (plains bison). RESULTS: We report much higher infection intensities and parasite species diversity in commercial bison herds than previously reported in beef cattle herds grazing similar latitudes. Predominant trichostrongyle parasite species in western Canadian commercial bison herds are those commonly associated with Canadian cattle, with Ostertagia ostertagi being the most abundant followed by Cooperia oncophora. Combined with high fecal egg counts in many herds, this is consistent with significant clinical and production-limiting gastrointestinal parasitism in western Canadian bison herds. However, Haemonchus placei was the most abundant species in five of the production groups. This is both surprising and important, as this highly pathogenic blood-feeding parasite has not been reported at such abundance, in any livestock species, at such northerly latitudes. The presence of Trichostrongylus axei as the most abundant parasite in four herds is also unusual, relative to cattle. There were striking differences in parasite communities between the EINP and commercial bison herds. Most notably, Orloffia bisonis was the predominant species in the wood bison herd despite being found at only low levels in all other herds surveyed. CONCLUSIONS: This study represents the most comprehensive description of parasite communities in North American bison to date and illustrates the power of deep amplicon sequencing as a tool to study species diversity in gastrointestinal nematode communities.

Increased Parasitic Load in Captive-Released European Bison (Bison bonasus) has Important Implications for Reintroduction Programs.

Captive-bred animals, widely used in reintroduction programmes, are often immunologically naïve and more susceptible to pathogens. We analysed infection of invasive blood-sucking nematode Ashworthius sidemi in captive-bred European bison (Bison bonasus) released to the wild in the Bialowieza Forest (Poland). Mean A. sidemi infection intensity of released bison (29,137 nematodes) was over threefold higher than in wild bison (8756). It indicates a rapid acquisition and increase in the infection intensity in previously dewormed bison released from captivity. Thus, reintroduction programmes should consider the impact of pathogens and involve controlled exposure of captive animals to specific parasites prior to release.

Gastrointestinal parasites of captive European bison Bison bonasus (L.) with a sign of reduced efficacy of Haemonchus contortus to fenbendazole.

The history of European bison Bison bonasus Linnaeus, 1758 has been stormy since its extinction in the wild after the First World War. Due to the fact that the species was restored from just 12 founders, further expansion has suffered from low genetic variability, rendering the bison vulnerable to various pathogens due to inbreeding depression. Parasites are recognised as a key biological threat to bison population. Thus, parasitological examination including monitoring of the level of anthelmintic resistance in a herd should be a routine procedure involved in management and protection of European bison. This study was conducted in a group of 27 bison kept in a European bison breeding centre in Sweden. In April 2015, a faecal egg count reduction test (FECRT) was performed in animals with ≥ 100 gastrointestinal nematode (GIN) eggs per gram faeces, to determine effectiveness of fenbendazole (FBZ) treatment. Additionally, the third stage larvae were cultured for molecular examination by a conventional PCR as well as by real-time quantitative PCR (q-PCR) for detection of the blood-sucking nematode Haemonchus contortus. Faecal sampling was conducted 1 day before and 8 days after deworming each animal. Anthelmintic treatment turned to be entirely efficient toward intestinal nematodes of genera Nematodirus and Trichuris, whereas shedding of strongylid eggs from the subfamily Ostertagiinae was reduced from 81 to 30%. Polymerase chain reaction (PCR) on cultured third-stage larvae (L3) before treatment was positive for H. contortus, Ostertagia ostertagi and Cooperia oncophora, whereas post-treatment examination revealed exclusively the DNA of H. contortus. Thus, only H. contortus was involved in post-treatment faecal egg count (FEC). FECRT showed that the reduction in strongylid FEC to FBZ in the examined bison herd was 87% (95%-confidence intervals [95% CI] = 76-93), suggesting reduced efficacy of FBZ to strongylid GIN including mainly H. contortus.

First Toxoplasma gondii isolate from an aborted foetus of European bison (Bison bonasus bonasus L.).

The study was performed on a male European bison (Bison bonasus bonasus L.) foetus spontaneously aborted at the fourth or fifth month of pregnancy in the Bialowieza Forest. Serum samples from the foetus and mother revealed the presence of antibodies against T. gondii (S/P% = 88% and 75%, respectively). Mobile extracellular tachyzoites were first observed in a Vero cell culture, 110 days following inoculation of brain homogenate. PCR amplification with TGR1E1 and TGR1E2 primers confirmed the presence of T. gondii DNA, which was classified as Type I by PCR-RFLP genotyping. The sequences of 18S ribosomal RNA (18S rRNA) and 5.8S ribosomal RNA (5.8S rRNA) genes; internal transcribed spacer 1 (ITS1) and internal transcribed spacer 2 (ITS2), obtained from T. gondii isolate, have been deposited in GenBank (accession number KX459518.1). This is the first in vitro isolation and molecular identification of T. gondii from an aborted European bison foetus. The origin of this protozoan isolate indicates that the species is a significant threat to the European bison conservation program implemented in the Bialowieza Forest.

Interrelationships of Dictyocaulus spp. in Wild Ruminants with Morphological Description of Dictyocaulus cervi n. sp. (Nematoda: Trichostrongyloidea) from Red Deer, Cervus elaphus.

Lungworms from the genus Dictyocaulus cause parasitic bronchitis (dictyocaulosis) characterized by coughing and severe lung pathology in both domestic and wild ruminants. In this study we investigated the interrelationships of Dictyocaulus spp. from European bison (Bison bonasus L.), roe deer (Capreolus capreolus), and red deer (Cervus elaphus) by nucleotide sequence analysis spanning the 18S RNA gene (small subunit [SSU]) and internal transcribed spacer 2 (ITS2) regions of the ribosomal gene array as well as the mitochondrial cytochrome c oxidase subunit 1 (cox1). Molecular analyses of sequence data obtained partly with novel primers from between 10 and 50 specimens from each host were carried out. Bayesian inference analysis revealed that each host species was infected with different genotypes. Analysis of cox1 sequence data showed a diverse genetic background and high evolutionary potential of Dictyocaulus taxa. Data from lungworms of European bison revealed a distinct genotype of Dictyocaulus viviparus, whereas Dictyocaulus capreolus was only found in roe deer. In contrast, red deer were infected with a taxon with unique SSU, ITS2, and cox1 sequences. These results indicate the occurrence of a novel genotype from red deer, which differs significantly from the National Center for Biotechnology Information reference sequence of Dictyocaulus eckerti. The molecular evidence was consistent with a morphological study with description and imaging of Dictyocaulus cervi n. sp. recovered from red deer. Dictyocaulus cervi n. sp. can be distinguished from D. eckerti on the basis of the absence of cervical papillae, the occurrence of a single ring of 4 symmetrical submedian cephalic papillae, length of the tail in females, morphometry of the female reproductive system, and measurements of gubernacula in males. In conclusion, our findings further strengthen the idea that the genetic complexity and diversity among Dictyocaulus lungworms infecting wildlife ruminants is larger than previously believed and warrants further investigation.

The first detection of the tick-borne encephalitis virus (TBEV) RNA in Dermacentor reticulatus ticks collected from the lowland European bison (Bison bonasus bonasus L.).

Tick borne encephalitis virus (TBEV) (Flaviviridae, Flavivirus) is the causative agent of tick-borne encephalitis (TBE), a potentially fatal neurological infection. The disease is endemic in a large region in Eurasia, where is transmitted mainly by hard ticks: Ixodes ricinus and I. persulcatus. It is known that also Dermacentor reticulatus is involved in a circulation of TBEV, but the knowledge of its importance in the TBE epidemiology is still insufficient. The Bialowieza Primeval Forest is located in eastern Poland and it is a well-known endemic focus of tick-borne encephalitis. The aim of this study was to identify the prevalence of tick-borne encephalitis virus (TBEV) in Dermacentor reticulatus ticks collected from European bison (Bison bonasus bonasus), an important host of hard ticks in the Bialowieza Primeval Forest. In the years 2008-2009, a total of 114 adult D. reticulatus ticks were collected from 7 European bison and examined individually for the presence of TBEV RNA using nested RT-PCR assay. Positive results were noted in 18.42% of ticks. This is the first record of TBEV infection in ticks collected from European bison.

Variations in cercarial production and the level of in vitro activation of metacercariae of two different isolates of Fasciola hepatica.

Fasciola hepatica infections cause large economic losses and are a serious veterinary medicine problem in many regions of the world. Recent studies examining fascioliasis in the bison population from Bialowieza National Park have shown that the prevalence of infection with this parasite is up to 100%. Liver flukes isolated from bison from Bialowieza National Park in Poland were compared with a fluke strain originally obtained from the Central Veterinary Laboratory, Weybridge, UK, to determine variations in cercarial production and establish the ability of their metacercariae to activate in vitro. Some small differences in cercarial production between the two isolates are shown, while significant differences in the ability of their metacercariae to activate in vitro were observed.

The parasitic fauna of the European bison (Bison bonasus) (Linnaeus, 1758) and their impact on the conservation. Part 1. The summarising list of parasites noted.

During the current century, 88 species of parasites have been recorded in Bison bonasus. These are 22 species of protozoa (Trypanosoma wrublewskii, T. theileri, Giardia sp., Sarcocystis cruzi, S. hirsuta, S. hominis, S. fusiformis, Neospora caninum, Toxoplasma gondii, Cryptosporidium sp., Eimeria cylindrica, E. subspherica, E. bovis, E. zuernii, E. canadensis, E. ellipsoidalis, E. alabamensis, E. bukidnonensis, E. auburnensis, E. pellita, E. brasiliensis, Babesia divergens), 4 trematodes species (Dicrocoelium dendriticum, Fasciola hepatica, Parafasciolopsis fasciolaemorpha, Paramphistomum cervi), 4 cestodes species (Taenia hydatigena larvae, Moniezia benedeni, M. expansa, Moniezia sp.), 43 nematodes species (Bunostomum trigonocephalum, B. phlebotomum, Chabertia ovina, Oesophagostomum radiatum, O. venulosum, Dictyocaulus filaria, D.viviparus, Nematodirella alcidis, Nematodirus europaeus, N. helvetianus, N. roscidus, N. filicollis, N. spathiger, Cooperia oncophora, C. pectinata, C. punctata, C. surnabada, Haemonchus contortus, Mazamastrongylus dagestanicus, Ostertagia lyrata, O. ostertagi, O. antipini, O. leptospicularis, O. kolchida, O. circumcincta, O. trifurcata, Spiculopteragia boehmi, S. mathevossiani, S. asymmetrica, Trichostrongylus axei, T. askivali, T. capricola, T. vitrinus, Ashworthius sidemi, Onchocerca lienalis, O. gutturosa, Setaria labiatopapillosa, Gongylonema pulchrum, Thelazia gulosa, T. skrjabini, T. rhodesi, Aonchotheca bilobata, Trichuris ovis), 7 mites (Demodex bisonianus, D. bovis, Demodex sp., Chorioptes bovis, Psoroptes equi, P. ovis, Sarcoptes scabiei), 4 Ixodidae ticks (Ixodes ricinus, I. persulcatus, I. hexagonus, Dermacentor reticulatus), 1 Mallophaga species (Bisonicola sedecimdecembrii), 1 Anoplura (Haematopinus eurysternus), and 2 Hippoboscidae flies (Lipoptena cervi, Melophagus ovinus). There are few monoxenous parasites, many typical for cattle and many newly acquired from Cervidae.

The parasitic fauna of the European bison (Bison bonasus) (Linnaeus, 1758) and their impact on the conservation. Part 2. The structure and changes over time.

During the last century the recorded parasite fauna of Bison bonasus includes 88 species. These are 22 species of protozoa, 4 trematode species, 4 cestode species, 43 nematode species, 7 mites, 4 Ixodidae ticks, 1 Mallophaga species, 1 Anoplura, and 2 Hippoboscidae flies. There are few monoxenous parasites, the majority of parasites are typical for other Bovidae and Cervidae species and many are newly acquired from Cervidae. This is an evident increased trend in the parasite species richness, in both the prevalence and intensity of infections, which is associated with the bison population size, host status (captive breeding or free-ranging) and the possibility of contact with other ruminant species. In light of the changes to parasite species richness during the last decades, special emphasis shall be given to new parasite species reported in European bison, their pathogenicity and potential implications for conservation.

Migrations and the introduction of wild ruminants as a source of parasite exchange and emergence of new parasitoses.

The relationship between European bison and cervidae is a good model for studies on the influence of migration and introduction of new species on the helmhninthofauna of wild ruminants and the occurrence of new parasitoses. Changes in the helminthofauna of bison and deer under the influence of changes in the environment and living conditions, as well as the introduction and migration of other species, are discussed in detail. The exchange of helminths between bison, cervids and domestic ruminants is demonstrated. Examples of helminth introduction from specific Cervidae species, the formation of the new host-parasite systems and the appearance of new parasitoses are also presented.

Coccidia (Apicomplexa: Eimeriidae) of the lowland European bison Bison bonasus bonasus (L.).

Coprological studies conducted between 2007 and 2011 in free-roaming and captive European bison Bison bonasus (Linnaeus, 1758) from Poland revealed 11 species of Eimeria infecting the host, i.e., Eimeria alabamensis, Eimeria auburnensis, Eimeria bovis, Eimeria brasiliensis, Eimeria bukidnonensis, Eimeria canadensis, Eimeria cylindrica, Eimeria ellipsoidalis, Eimeria pellita, Eimeria subspherica, and Eimeria zuernii. The typical host for all isolated species is cattle. The most prevalent species was E. bovis (29.7%), while E. brasiliensis was the rarest (0.5%). Five of the species (E. bovis, E. bukidnonensis, E. canadensis, E. ellipsoidalis, E. zuernii) have been observed previously in bison by other authors, 3 species were noticed by us in bison previously (E. alabamensis, E. cylindrica, E. pellita), while for 3 species (E. auburnensis, E. brasiliensis, and E. subspherica) these are new host and locality records. Oocysts of two species (E. brasiliensis, E. bukidnonensis) were noted only in the feces of bison kept in captivity. Moreover, the prevalence of positive samples was higher in the group of captive animals (55.4%) in comparison with the free-roaming herds (29.5%); although, oocysts per gram (OPG), counted with the conventional McMaster technique, was comparable in both groups, reaching maximally 6550 and 6400 in free-roaming and captive individuals, respectively. Overall, 142 fecal samples from 424 samples examined were positive for Eimeria (prevalence=33.5%). Age-related analysis revealed a higher percentage of Eimeria spp. positive samples and higher OPG values in bison under 1 year old as compared to older individuals (93.3% and 50-4050; 37.3% and 50-550, respectively). Additionally, greater eimerian species diversity was present among calves in comparison with older bison. In most cases single-species infections were observed (59.8%) with a predominance of E. bovis (85.9%). Multiple-species infections consisted of 2-7 species, usually including E. bovis. The observation was made that E. bovis infection appears conducive to the host acquiring more eimerian species. No symptoms of clinical coccidiosis occurred during the study.

Mitochondrial DNA haplotype analysis of liver fluke in bison from Bialowieza Primaeval Forest indicates domestic cattle as the likely source of infection.

We have determined the mitochondrial genotype of liver fluke present in Bison (Bison bonasus) from the herd maintained in the Bialowieza National Park in order to determine the origin of the infection. Our results demonstrated that the infrapopulations present in the bison were genetically diverse and were likely to have been derived from the population present in local cattle. From a consideration of the genetic structure of the liver fluke infrapopulations we conclude that the provision of hay at feeding stations may be implicated in the transmission of this parasite to the bison. This information may be of relevance to the successful management of the herd.

Nematodes of the large intestine of the European bison of the Bialowieza National Park.

The present study was conducted on 31 males and females of the European bison, eliminated during the winter seasons 2007-2011 in the Bialowieza Primeval Forest, Poland. The caeca of 14 free-ranging bison, aged from 3 months up to 16 years, the most favorable infection site for the large intestine nematodes, were investigated during the winter of 2007/2008. The parasitological autopsies of the large intestines of 9 free-ranging bison aged from 5 months up to 10 years as well as 9 bison kept in the close reserves aged from one up to 20 years were done during the winter seasons of 2008-2011 to determine localization of nematodes in large intestine and the total intensity of parasite infection. Five species of nematodes (i.e., Trichuris ovis, Oesophagostomum venulosum, O. radiatum, Ashworthius sidemi, Nematodirus helvetianus) were found in dissected caecum of bison culled during the winter of 2007/2008. During the seasons of 2008-2010, 6 species of nematodes were found in the large intestine of bison (i.e., T. ovis, O. venulosum, O. radiatum, A. sidemi, N. roscidus and Bunostomum trigonocephalum). We did not find any nematodes in the lumen of the large intestine of captive bison culled during the seasons of 2010/2011. The results of the present study indicate that the intensity of infection by the large intestine nematodes of the European bison in the Bialowieza Primeval Forest has stayed at the comparable level throughout the last 20 years; however the number of nematode species has increased. The observed level of parasitic infection is typical of subclinical parasitoses.