Caracterização biológica e genotípica de isolados de Toxoplasma gondii de suínos naturalmente infectados do Rio Grande do Sul, Brasil

Abstract

The protozoan Toxoplasma gondii can infect a wide range of animal species, including man. Among domestic animals, pigs have greater importance due to the risk of human infection by ingestion of raw or undercooked meat and handmade sausages. The aim of the study was the isolation and genotypic characterization of T. gondii from small farms pigs naturally infected, intended for human consumption. Serum samples from pigs (100) of 58 farms in different of municipalities southern Rio Grande do Sul were analyzed by indirect fluorescence antibody test (IFAT ≥ 64). 36.0% of the animals sampled were seropositive with antibody titers from 64 to 2048. To isolate the parasite, bioassays in mice were performed using a pool of seropositive pig tissues (heart and brain). From the 36 bioassays, 17 isolated (47.2%) were obtained. 41.2% of these (7/17) proved to be highly virulent to the inoculated mice, causing 100% mortality. Tachyzoites were found in peritoneal exudates, livers and lungs. The remaining isolates (10/17) did not cause clinical signs, but antibodies were detected with titers from 16 to 512 (IFAT ≥ 16), and cysts of the parasite in the brains and/or livers of the infected mice. For the genotypic characterization of all isolates (17) the PCR-RFLP technique was used in the locus 5'3'SAG2 that identifies genotypes I, II and III. Genotypes Type I (29.4% - 5/17) and III (70.6% - 12/17) were identified and there was no detection of Type II. Among the isolates characterized as Type I, four (80.0%) killed the mice and (20.0%) did not kill any animal. Only three isolates of Type III (25.0%) were virulent, causing the death of animals, which did not occur with the remaining nine (75.0%). Among 17 isolates, five were genotyped with more markers up to this moment, in addition 5'3'SAG2 (SAG1, alt. SAG2, BTUB, GRA6, c22-8, c29-2, L358, PK1, Apico e CS3). Five different genotypes were identified, three of them having already been described in Brazil (Types III, BrII and BrIV) and two being newly identified genotypes. The new genotypes, BrII and BrIV were highly virulent, able to kill 100% of the infected mice. The isolate Type III was avirulent and cystogenic. Using the marker CS3, it was found that the isolates which presented alleles I and u-1 were virulent, while those with only III were only cystogenic. Genotypic characterization by PCR-RFLP with more markers is more accurate, since it allows the identification of atypical genotypes. This study reveals that small farms pigs in the region might serve as a source of human infection by the parasite, once they are infected by a population of T. gondii which is diversified regarding virulence characteristics and genotype.