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This study aimed to genetically characterize Toxoplasma gondii isolates obtained from free-range chickens reared in the metropolitan region of the state of Rio de Janeiro, Brazil, and to evaluate the morbidity and histological changes associated with these isolates in mice. A mouse bioassay was used to isolate T. gondii from a pool of tissue samples (brain, heart, and thigh muscles) collected from 163 chickens. The 36 isolates obtained were genetically characterized by restriction fragment polymorphism (PCR-RFLP) analysis of the SAG1, 5'-3'SAG2, aSAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, Apico, and CS3 genomic regions. Seventeen atypical genotypes were identified and nine of them were reported for the first time. All identified genotypes caused clinical signs and histological changes in mice, with the majority being associated with high cumulative morbidity (65%) and severe or very severe histological changes (76%). The exclusive identification of atypical genotypes, with a predominance of new genotypes, indicates great genetic diversity of T. gondii in the region studied. In addition, the finding that all identified genotypes caused clinical signs and often severe histological changes in mice suggests potentially relevant virulence of these strains.

The environmental contamination of Toxoplasma gondii in an endemic area in Brazil was mapped by georeferencing isolates from chickens in farms in the Southeast of the state of Rio de Janeiro. Tissue samples obtained from 153 adult chickens were analyzed by the mouse bioassay for T. gondii infection. These animals were reared free-range on 51 farms in the municipalities of Rio Bonito and Maricá. The ArcGIS kernel density estimator based on the frequency of T. gondii-positive chickens was used to map the environmental contamination with this parasite. A questionnaire was applied to obtain data on the presence and management of cats and the type of water consumed. Of the farms studied, 64.7% were found to be located in areas of low to medium presence of T. gondii, 27.5% in areas with a high or very high contamination level and 7.8% in non-contaminated areas. Additionally, 70.6% kept cats, 66.7% were near water sources and 45.0% were in or near dense vegetation. Humans used untreated water for drinking on 41.2% of the farms, while all animals were given untreated water. The intensity of environmental T. gondii contamination was significantly higher on farms situated at a distance >500 m from water sources (P=0.007) and near (≤500 m) dense vegetation (P=0.003). Taken together, the results indicate a high probability of T. gondii infection of humans and animals living on the farms studied. The kernel density estimator obtained based on the frequency of chickens testing positive for T. gondii in the mouse bioassay was useful to map environmental contamination with this parasite.