Forest Density and Invasive Carnivores Are Related to Trichinella Infection in Wild Boars in Poland

The purpose of this study was to investigate and update the spatial distribution of <i>Trichinella</i> spp. in wild boars tested between 2015 and 2022 and to test the correlation of the population density of chosen animals (wild boars, red foxes (<i>Vulpes vulpes</i>), raccoon dogs (<i>Nyctereutes procyonoides</i>), and European badgers (<i>Meles meles</i>)) with the prevalence of <i>Trichinella</i> spp. in wild boars in Poland. In addition, to understand the distribution of infected animals, we sought to see if there were a correlation of <i>Trichinella</i> spp. infections in wild boars with land cover type. Among the wild carnivore species analyzed, only the population density of the raccoon dog (<i>Nyctereutes procyonoides</i>)-an invasive alien species-was significantly associated with infection rates in wild boars, particularly at the regional scale. As scavengers and competent reservoir hosts for all four European <i>Trichinella</i> species, raccoon dogs are likely to play a key role in the sylvatic transmission cycle. The positive rate of <i>Trichinella</i> spp. infection in wild boars during 2015-2022 was 0.22%, compared to 0.3% in 2009-2016. Moreover, forest density was positively correlated with infection rates, underlining the role of forest habitats in sustaining <i>Trichinella</i> transmission.