The nation’s feral swine population poses a significant risk for introduction of trichinella and toxoplasma into domestic swine herds as the range of the two groups increasingly overlaps.

Nationwide serological and parasitological surveys of captured feral swine indicate a prevalence of 2.7% for trichinella and 17% for toxoplasma.

This potential introduction of diseases into domestic herds from feral swine could cost the swine industry millions of dollars in veterinary care, quarantines, restrictions on animal movement and market loss.

Trichinella spiralis and Toxoplasma gondii are important zoonotic parasites that infect warm-blooded animals, including swine and humans worldwide.

A cross-sectional serological survey was performed to determine the prevalence of these parasites in feral swine and to understand the risk of transmission to domestic swine via commingling. A total of 3,262 serum samples were collected from 32 states and results are reported from 26 states.

Figure 1 depicts the geographical regions of distribution of pastured pig operations and feral swine that tested positive for trichinella. A small proportion of feral swine (0.6%) tested positive for both parasites.

Table 1 shows there was no significant difference in infection levels between male and female swine for either parasite.

The infection level for toxoplasma was much higher in adults than in sub-adults or juveniles, a trend that was not seen in trichinella-infected swine.

Feral swine infected with toxoplasma were widespread across the south and Midwest, and less common in the arid west.

Trichinella infection levels were much higher in the south than in the Midwest and higher in the Midwest than in the west.

Species distribution levels for both parasites were most commonly found in the south and the Midwest.

Researcher: Dolores Hill, USDA, ARS, Beltsville, MD. For more information, contact Hill by phone (301) 504-8770, fax (301) 504-5558 or e-mail