Toxoplasma gondii in slaughtered sheep: a study of parasite prevalence, isolation, genotyping, virulence, and potential health risks to butchers in India.

Abstract

Toxoplasma gondii is a foodborne parasite that poses a significant global public health risk, with sheep acting as a key intermediate host in its transmission. Due to limited information in India, this study aimed to assess the T. gondii prevalence in slaughtered sheep, isolate parasites from meat, conduct molecular and phenotypic characterization of the strains, and evaluate the risk of infection for butchers in slaughterhouses. A total of 485 sheep (sera and brain samples) and 107 butchers (sera and PBMCs) were screened for antibodies using various serological tests (ELISA, MAT, and IFAT) and viable parasites through mouse bioassay. Among the sheep, 160 (33%) tested seropositive, with antibody titers ranging from 100 to 3200; 32 (21.2%) had low IgG avidity, and 10 were positive for the B1-gene PCR. In the butchers, 33 (30.8%) tested positive for antibodies showing titers from 100 to 3200, and 8 (26.6%) showed low IgG avidity; however, none tested positive for parasite DNA. Interrater agreement between different serological tests, using the IFAT as the reference test, revealed good agreement (kappa value κ ∼0.8) for MAT and ELISA. Using a mouse bioassay, we isolated 2 viable T. gondii isolates (TgOv1 and TgOv2) from 160 brain samples of seropositive sheep; however, no viable parasites were recovered from 33 human samples. Both the isolates were genotyped as clonal type II based on PCR-RFLP using 10 markers: SAG1, 5'-SAG2, 3'-SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and CS3. The genotyping results were confirmed by mouse virulence studies, which showed that both isolates were non-virulent in mice. Additionally, we found that older age, longer work experience, lack of protective gear, and low awareness of meatborne diseases significantly contribute to T. gondii seropositivity in butchers. Overall, this study demonstrates that T. gondii is highly prevalent with low genetic diversity, highlighting a potential health risk to butchers and consumers.