Isolate designation and characterization of Toxoplasma gondii isolates from pigs in the United States.

Pigs are considered to be the most important meat source of Toxoplasma gondii for humans in the United States. In the present study, 168 T. gondii isolates (designated TgPgUs15-182) from various sources were genotyped using 10 polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) markers (SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and Apico). Genotyping data from an additional 14 isolates collected from T. gondii-infected pigs in Maryland were included for analysis. Nine genotypes (1-9) were recognized from the 182 T. gondii isolates. Most (56%, 102) isolates were clonal Type II (genotypes 1 and 2) and 27% (49) were clonal Type III (genotype 3) strains. Genotype 4 had Type II alleles, with the exception of Type I alleles at loci Apico and L358. Eight isolates (genotype 5) from Iowa had a combination of alleles I, II, and III at different loci. The remaining 6 isolates were divided into genotypes 6-9 and had a combination of different alleles. Eight of the 9 genotypes were previously reported in different animal species and geographic regions. In conclusion, along with the predominance of clonal Type II and III strains, a few diverse, previously unrecognized T. gondii lineages were found circulating in domestic pigs used for human consumption.