Enteropathogenic Yersinia spp. and Salmonella spp. in Swedish wild boars : the presence and molecular epidemiology

Abstract: Wild boars are reported as carriers of several zoonotic agents. The aims of this thesis was to investigate the presence of the foodborne enteropathogens Salmonella spp., Yersinia (Y.) spp. and E. coli O157:H7 in Swedish wild boars, the influence of potential risk factors presumably associated with their occurrence, the presence of Yersinia spp. and Salmonella spp. in minced meat, and to establish a method for molecular epidemiological studies (MLVA). The thesis includes studies on lymphatic tissue and faeces from 178 wild boars and 32 samples of wild-boar minced meat. MLVA was evaluated on 254 isolates of Y. enterocolitica from several sources. Further, the wild boar populations were characterized with respect to four factors that possibly may be associated with the presence of enteropathogens in the wild boar. A PCR-based protocol for the detection of enteropathogenic Yersinia spp. and Salmonella spp. was developed and evaluated. The protocol offered the possibility to obtain molecular epidemiological data of Yersinia spp. by MLVA on enrichment broths. In total, 91 (51.1%) of the sampled wild boars carried the enteropathogens investigated and 46, 37 and 32 animals were PCR-positive for the presence of Y. enterocolitica, Y. pseudotuberculosis, and Salmonella spp., respectively. The subsequent cultivation yielded a total of 28 isolates of Salmonella spp., 10 isolates of Y. enterocolitica and 13 isolates of Y. pseudotuberculosis. None of the investigated risk factors were associated with the presence of these enteropathogens. However, a strong association between high levels of artificial feeding and high population densities was seen and the practice of leaving slaughter waste out in nature was found to be common among the hunters. In the new protocol, a positive selection for motile bacteria was used and seemed favourable in the detection of Y. enterocolitica and Salmonella spp. but not in the detection of Y. pseudotuberculosis. Further, MLVA performed directly on the enrichment broth seemed promising. MLVA on the isolates demonstrated a close resemblance between two human isolates and those obtained from domestic pigs whereas one rodent isolate was identical to that from pigs in the same farm. In conclusion, human enteropathogens are present in a majority of the Swedish wild boars which may be of concern for the public health. The findings warrants further surveillance on the enteropathogens present and the new protocol presented within this thesis may be useful to obtain molecular epidemiological data for future reference in e.g. outbreak investigations.