Toxoplasma gondii contamination at an animal agriculture facility: Environmental, agricultural animal, and wildlife contamination indicator evaluation

Toxoplasma gondii is a parasite of significant public health importance. We attempted to detect T. gondii contamination and assess advantages and disadvantages of contamination indicators through surveilling soil, wildlife, cats (Felis catus), and cows (Bos taurus) on a farm in Tennessee, U.S. in 2016 and 2017. Twenty-two soil samples were collected from the farm and subjected to oocyst flotation, DNA extraction, and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) targeting 18S ribosomal RNA (18S rRNA) gene to detect and identify T. gondii. Three samples (13.6%) were positive for the parasite; however, T. gondii DNA was not consistently detected from repeated tests. Blood samples were collected from small mammals, cats, and mesopredators live-trapped on the farm, and serum from 30 of the farm's cows were obtained. Serological testing by the modified agglutination test (MAT; cutoff 1:50) found 2.5% (1/40) of small mammals, 52.9% (9/17) of raccoons (Procyon lotor), and 50% (1/2) of domestic cats were seropositive for T. gondii antibodies. No antibodies were found in 16 opossums (Didelphis virginiana), two skunks (Mephitis mephitis), and 30 cows. Small mammal tissue samples were subjected to PCR-RFLP detection. Four out of 29 (13.7%) tissue samples were positive for T. gondii; however, T. gondii DNA was not consistently detected during repeated PCR-RFLP testing. Our results indicate the ability to detect T. gondii varies greatly by contamination indicator. We found detection of soil oocysts to be challenging, and results suggest limited utility of the method performed. The ability to detect T. gondii in animals was highly variable among species. Our research emphasizes the importance of a holistic approach when surveilling for T. gondii to compensate for shortcomings of each contamination indicator. Future research should be conducted to further investigate the most effective T. gondii surveillance methods and species with increased sample sizes at other agricultural facilities.
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Highlights • We investigated T. gondii contamination at a farm and the efficacy of T. gondii detection indicators through examining soil, small mammals, mesopredators, domestic cats, and agricultural animals • Soil oocyst detection was low suggesting limited utility of the method performed in the study region • Small rodents and agricultural animals had low detection of T. gondii • Mesopredators (i.e., raccoons and domestic cats) had the greatest affinity for T. gondii detection out of all tested animals and fomites • Multiple indicators of potential contamination should be examined when trying to detect T. gondii