Toxoplasma Gondii Detection In Domestic And Wild Animals: Methods Development And Application For Epidemiological Investigations

Abstract

Toxoplasma gondii infection remains a condition of interest in both human and veterinary medicine despite having recently celebrated its first century of recognition. Toxoplasma is distinguished from intestinal coccidia in its utilization of intermediate hosts, causing disease in a wide spectrum of animals. Diagnosis is also more complicated as it localizes in numerous tissues in intermediate hosts and has only a brief period of oocyst shedding in infected felids. The inability to diagnose Toxoplasma infection by direct observation has led to a reliance on serological assays as the primary diagnostic method. Serological testing establishes a history of exposure to Toxoplasma, but does not definitively identify this as the genesis of the clinical signs of interest. The situation is more complicated in veterinary medicine by the decreasing availability of test methods that can be used across the range of animals susceptible to infection. The development of protein conjugates A, G and chimeric A/G allows the use of a human enzyme-linked immunosorbent assay for a range of animal species. When compared to established agglutination testing for the detection of anti-Toxoplasma IgG antibody, agreement between the two tests was determined to be very good, with a kappa value of 0.83 for the trial using proteins A and G separately and 0.81 when chimeric protein A/G was used. This technique demonstrated a seropositivity of 38.5% when utilized to examine the occurrence of Toxoplasma exposure among hunter-killed white-tailed deer in New York State from 2010, indicating a notable level of exposure in this population. Further analysis revealed older deer are more likely to have seroconverted, consistent with a model of significant horizontal transmission by oocysts. No significant differences in infection based on sex or local human population density were noted. A quantitative real-time PCR assay was developed based on the Toxoplasma B1 gene, but did not detect the presence of parasite DNA in serum samples from seropositive dogs and sheep. These ELISA and PCR assays are valuable both to veterinary diagnosticians in individual cases and to investigators studying Toxoplasma prevalence in a broad spectrum of domestic and wild animals.