Isolation of Toxoplasma gondii from the masseter muscles of equines destined for human consumption in a slaughterhouse in southern Brazil

The aim of this study was to isolate Toxoplasma gondii from equids destined for slaughter in a Brazilian slaughterhouse. A total of 354 equids were analyzed, with blood samples collected from all the animals and samples of masseter muscle and brain tissue collected from 319 animals. A serological test was conducted to detect equids with specific antibodies for T. gondii. Molecular detection of T. gondii by nested PCR was performed on the tissue samples collected. Tissue samples were tested by murine bioassay in an attempt to isolate either the parasite or the parasite DNA. Real-time PCR was performed on the brain samples from 11 mice which seroconverted after inoculation, to quantify the parasitic DNA. Genotyping was performed in masseter tissues samples from positive horses or from tissues of mice inoculated with masseter. The seroprevalence of T. gondii infection was 19.2%. Nested PCR showed that 5.3% of the equines and 28.8% of the mice from the bioassays were positive for T. gondii. Nine masseter muscle samples were positive (either on nested-PCR or in bioassay). Genotyping by PCR–RFLP was attempeted on all 12 isolates and was successful in seven, revealing six recombinant and one atypical genotype. The detection of T. gondii DNA in masseter muscle tissue of horses destined for consumption clearly indicates a risk to human health.