Surveillance of feral swine for Trichinella spp. and Toxoplasmagondii in the USA and host-related factors associatedwith infection

Trichinella spp. and Toxoplasma gondii are important zoonotic parasites that infect warmblooded animals and humans worldwide. Among domesticated food animals, pigs are themain host for Trichinella spiralis. Pigs, chickens, sheep, and goats are known to be infectedwith T. gondii at varying rates, depending on husbandry. Infections in wildlife with theseparasites are generally higher than in domesticated species. Feral swine act as reservoirsof infection in the sylvatic ecosystem for Trichinella spp. and T. gondii, acting as sourcesof infection for peridomestic carnivores whose home ranges overlap with domestic pigs.Feral swine can have direct contact with non-biosecure domestic pigs, presenting oppor-tunity for direct disease transmission through cannibalistic behavior. Determination of theprevalence of Trichinella spp. and T. gondii infection in feral swine is needed to understandthe risk of transmission of these parasites to domestic pigs. A cross-sectional serologi-cal survey was conducted between 2006 and 2010 to estimate the antibody prevalenceof Trichinella spp. and T. gondii and risk factors associated with infection in feral swinein the USA. Serum samples were tested from 3247 feral pigs from 32 states; results arereported from 26 states. Maximum entropy ecological niche modeling and spatial scanstatistic were utilized to predict the geographic range and to examine clusters of infectionof Trichinella spp. and T. gondii in feral pigs. The seroprevalence of antibodies to Trichinella spp. and T. gondii was 3.0% and 17.7%, respectively. Species distribution modeling indicatedthat the most probable distribution areas for both parasites was similar, concentrated pri-marily in the South and the Midwest regions of the USA. A follow up survey conductedduring 2012–2013 revealed that 2.9% of 984 sampled feral swine were seropositive for Trichinella spp., and 28.4% were seropositive for T. gondii. Three hundred and thirty (330)tongues were collected from the 984 sampled animals during 2012–2013; 1.81% were tissuepositive for T. spiralis muscle larvae; no other genotypes were found. The potential existsfor introduction of these pathogens into domestic herds of non-biosecure domestic pigs asa result of increasing overlap of the range of feral pigs with non-biosecure domestic pigsproduction facilities in the USA