Low seroprevalence of Toxoplasma gondii in feral pigs from a remote island lacking cats

Serum samples from 1,264 feral pigs from Ossabaw Island, Georgia were initially screened for antibodies to Toxoplasma gondii by the modified agglutination test (MAT) using whole-formalinized tachyzoites and mercaptoethanol. Seropositive samples were also tested by the Sabin-Feldman dye test, the latex agglutination test (LAT), and the indirect hemagglutination test (IHAT). Ossabaw Island is a remote, barrier island located southeast of Savannah, Georgia. Antibodies to T. gondii were found in 11 (0.9%) of 1,264 pigs. The antibody titers were 1:20 (1 pig), 1:80 (2 pigs), 1:160 (2 pigs), 1:320 (4 pigs), and 1:640 (2 pigs) by the MAT, and 1:8 (2 pigs), 1:16 (3 pigs), 1:32 (1 pig), 1:64 (2 pigs), 1:128 (1 pig), and > or = 1:256 (2 pigs) by the Sabin-Feldman dye test. By the LAT, 5 pigs had a titer of > or = 1:64 and by the IHAT all 11 pigs had a titer of < 1:64. Antibodies (MAT titer, > or = 1:25) were found in 31 (18.2%) of 170 feral pigs from mainland Georgia. This seroprevalence on the mainland was significantly higher (P < 0.0001) as compared on Ossabaw Island. The markedly low prevalence of T. gondii on Ossabaw Island was attributed to the virtual absence of cats on the Island; only 1 domestic cat was known to be present.