Distribution and prevalence of antibodies to Trichinella spp. and Toxoplasma gondii in wild pigs (Sus scrofa) in the United States

Invasive wild pigs (Sus scrofa) are a reservoir for over 100 viral, bacterial, and parasitic pathogens that are transmissible to humans, livestock, domestic animals, and wildlife in North America. Numerous historical local surveys and results from a nation-wide survey (2006-2010) indicated that wild pigs in the United States act as reservoirs for Trichinella spp. and Toxoplasma gondii, two zoonotic pathogens of importance for human and animal health. Since that time, wild pig populations have expanded and increased in density in many areas. Population expansion of wild pigs creates opportunities for the introduction of pathogens to new areas of the country, increasing health risks. The goal of this study was to investigate the current geographic distribution and prevalence of Trichinella spp. and T. gondii antibodies in wild pigs using serum samples collected from 2014 to 2020. Serum samples from 36 states were tested for antibodies to Trichinella spp. (n = 7467) and T. gondii (n = 5984) using commercially available enzyme-linked immunosorbent assays. Seroprevalence for Trichinella spp. (12.4%, 927/7467) and T. gondii (40.8%, 2444/5984) are significantly higher compared to a previous 2006-2010 study across all regions. Results from this study also showed a lower seroprevalence (4.8%) for Trichinella spp. in the West region compared to the other regions (South: 13.4%; Midwest: 18.4%; Northeast: 19.1%). There were new detection records for antibodies to Trichinella spp. in 11 states, mostly in the West, Midwest, and Northeast regions compared to a previous study in 2014. Males and juveniles were less likely to be positive for Trichinella spp. antibodies, compared to females and older animals, respectively. Seroprevalence was similar for T. gondii across the regions (31.8-56%) with some states having particularly high seroprevalence (e.g., Hawaii 79.4% and Pennsylvania 68%). There were new T. gondii antibody detection records for 12 states, mostly in the West, Midwest, and Northeast regions. Adults were more likely than juveniles and subadults to be seropositive. These data confirm that the distribution and prevalence of antibodies for Trichinella spp. and T. gondii are increasing in the United States, likely driven by wild pig population growth and range expansion.