Parasitic infections in wildlife are affected by biological, ecological and anthropogenic factors and they may have important effects on both individuals and populations. In this paper we studied spread of sparganosis – the disease caused by the diphyllobothrid tapeworm from the genus Spirometra, whose importance is increasingly growing around the world. We analysed different factors influencing Spirometra erinaceieuropaei infection parameters in two carnivore hosts: raccoon dog (Nyctereutes procyonoides) and European badger (Meles meles). We found no differences in infection probability between studied hosts; however, European badger has significantly higher mean number of plerocercoid larvae than raccoon dog (35.4 and 4.2, respectively). For both host species we found significant differences in S. erinaceieuropaei prevalence between study sites: Białowieża Forest (BF), Knyszyn Forest (KF) and Augustów Forest (AF). Infection probability was also positively related to the proportion of wet habitats. Sparganosis prevalence decreased with time covered by the study; however, the significance of the temporal changes was confirmed only for raccoon dog. Spirometra erinaceieuropaei infection probability increased with the age of animals with the rate similar for both species, which suggests multiple infections. No sex difference in infection prevalence was found in both species. Our study revealed complex factors, both biological and environmental, involved in parasite transmission, spread and persistence in medium-sized carnivore hosts. Similar prevalence in studied species, may suggest similar probability of infection risk, but higher infection intensity in European badger may be related to much shorter co-evolution of this species with the parasite.