Prevalence of Toxoplasma gondii in dogs from Sri Lanka and genetic characterization of the parasite isolates

The prevalence of Toxoplasma gondii in 86 street dogs from Sri Lanka was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT) and found in 58 (67.4%) of 86 dogs with titers of 1:20 in eight, 1:40 in four, 1:80 in 10, 1:160 in 22, 1:320 in six, 1:640 in five, and 1:1280 or higher in three. Hearts, tongues, and brains (either separately or pooled) of 50 dogs with MAT titers of 1:40 were selected for isolation of T. gondii by bioassays in mice. For bioassays, canine tissues were digested in pepsin and homogenates were inoculated subcutaneously into mice; the mice receiving canine tissues were examined for T. gondii infection. In all, T. gondii was isolated from 23 dogs. Interestingly, dog organs varied in their capacity to induce T. gondii infection in mice, muscles producing more positive results than the brain. The T. gondii isolates obtained from 23 seropositive dogs were PCR-RFLP genotyped using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, a new SAG2, and an apicoplast marker Apico. Mixed infection with two genotypes was observed in one dog. Four genotypes were revealed, including three unique genotypes in addition to one belonging to the predominant Type III lineage. The 24 isolates were designated as TgDgSl 1-24.