Toxoplasma gondii infection in cats from São Paulo state, Brazil: seroprevalence, oocyst shedding, isolation in mice, and biologic and molecular characterization.

Cats are the most important hosts in the epidemiology of Toxoplasma gondii infections in humans and animals. Serologic and parasitological prevalence of T. gondii were determined in 237 cats from 15 counties in São Paulo state, Brazil. Antibodies to T. gondii were found in a 1:25 dilution of serum of 84 (35.4%) out of 237 cats by the modified agglutination test (MAT). Samples of brain, heart, tongue, and limb muscles (total 50 g) of 71 of the seropositive cats were pooled for each cat, digested in pepsin and bioassayed in mice. Faeces (1 g) from the rectum of each cat were examined microscopically for T. gondii-like oocysts and verified by bioassay in mice; T. gondii oocysts were found in the faeces of three (1.3%) of 237 cats. T. gondii was isolated from tissue homogenates of 47 cats. The DNA obtained from these 47 tissue isolates was characterized using the SAG2 locus: 34 (72.4%) isolates were type I, 12 (25.5%) were type III and one (2.1%) was mixed with types I and III. No type II isolates were detected. Most (23/34) of the type I isolates killed all infected mice and 7 of 12 type III isolates did not kill infected mice. Characterization of the SAG2 locus directly from tissue homogenates from 37 of 46 cats was successful. Genotypes obtained from these primary samples were the same as those from the corresponding isolates obtained in mice. Genotyping of the three oocyst isolates revealed that two were type I and one was type III. Molecular and biologic characteristics of T. gondii isolates from animals from Brazil are different from those from other parts of the world.