AbstractIntroductionCommon parasites of the European bison include gastro-intestinal and pulmonary nematodes, liver flukes (Fasciola hepatica), tapeworms, and protozoa of the genusCoccidia. This study compared the extensiveness and intensities of European bison parasitic invasions in three north-eastern Polish forests in different seasons and queried the role of parasitological monitoring in sanitary and hygienic control of feeding places.Material and MethodsFaecal samples were collected in the Białowieża, Knyszyńska, and Borecka Forests between 2014 and 2016, as were some from an area neighbouring the Białowieża Forest outside the Natura 2000 protected area. Parasites were detected in individual samples with the flotation, decanting and Baermann methods.ResultsThe eggs ofTrichostrongylidae,Aonchothecasp.,Nematodirussp.,Strongyloidesspp.,Trichurissp.,Monieziaspp., andFasciola hepatica; the larvae ofDictyocaulus viviparus; and the oocytes ofEimeriaspp. were identified. Significant variation in invasion intensity and diversity was seen by origin and season. The relationships were assessed first by univariable tests and next multivariately, when origin and season emerged as the major risk factors for exposure to most of the parasites.ConclusionThe differences in the level of parasitic infection between the forests did not have implications for its sufficiency to cause clinical symptoms. However, the associations and risk factors found enable the necessary preventive measures to be taken to protect the E. bison from exposure or decrease the risks. Additionally, parasitological monitoring is appropriate as the method of sanitary and hygienic control of European bison winter feeding places. Threats to public health through adventitious invasions by zoonotic factors such asF. hepaticahave been identified.