Molecular Survey of Selected Bacterial Respiratory Pathogens in Polish Wild Boars

Wild boar (Sus scrofa) is a widespread invasive species in Poland and may act as a reservoir for various pathogens, including those associated with the porcine respiratory disease complex (PRDC). As data on bacterial respiratory pathogens in wild boar populations, particularly co-infections, in Poland and other European countries remain limited, the main goal of our study was to examine the frequency of selected bacterial respiratory agents and their co-occurrence in lung samples collected from culled wild boars during hunting. Two hundred and fifty-three lung samples were analysed for the presence of genetic material of A. pleuropneumoniae, M. hyopneumoniae, M. hyorhinis, and G. parasuis. In total, 159 out of the 253 (62.8%; 95% CI: 56.6-68.8) wild boars were infected with at least one pathogen. In general, 73 (28.9%; 95% CI: 23.3-34.9) of wild boar lung samples tested positive for G. parasuis, 106 (41.9%; 95% CI: 35.7-48.2) were positive for M. hyopneumoniae, and 10 (4%; 95% CI: 1.9-7.1) were positive for M. hyorhinis. No evidence of A. pleuropneumoniae infection was detected in any of the examined lung samples. Infection with a single pathogen was detected in 129 (51%; 95% CI: 44.6-57.3) of sampled wild boars, whereas co-occurrence of two infectious bacterial agents was revealed in 30 animals (11.9%; 95% CI: 8.1-16.5). Among single-pathogen infections, the highest positivity rate was observed for M. hyopneumoniae (31.6%; 95% CI: 25.9-37.7), whereas the most frequent co-infection involved M. hyopneumoniae and G. parasuis (9.1%; 95% CI: 5.8-13.3). This investigation indicated that wild boar in the study area are potential hosts for bacterial agents associated with PRDC. It is worth highlighting that wild boars can contribute to the maintenance and/or dissemination of bacterial pathogens to humans (especially hunters) and domestic animals, and it is essential to maintain active surveillance of these infectious agents.