Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2007
Publication Date: 3/1/2008
Citation: Sundar, N., Cole, R.A., Thomas, N.J., Majumdar, D., Dubey, J.P., Su, C. 2008. Genetic diversity among sea otter isolates of Toxoplasma gondii. Veterinary Parasitology. 151:125-132. Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating undercooked meat from infected animals and food and water contaminated with oocysts. Toxoplasmosis causes mortality in many species of animals in the zoos, especially primates. Scientists at the Beltsville Agricultural Research Center and US Wildlife Service report genetic variability of Toxoplasma from sea otters and describe a new genotype of T. gondii. The results will be of interest to biologists, parasitologists, and veterinarians.
Technical Abstract: Sea otters (Enhydra lutris) have been reported to become infected with Toxoplasma gondii and at times succumb to clinical disease. The mode of marine contamination has been the subject of recent papers. Because of their susceptibility these animals can serve as a sentinel for contamination of marine waters with oocysts. Previous study of T. gondii isolates from California sea otters identified two genotypes including the clonal Type II and a new genotype named Type X. Here, we genotyped 38 T. gondii isolates from sea otters in two geographically distant locations (25 from California and 13 from Washington). Seven genotypes were identified using 10 PCR-RFLP genetic markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico, and by DNA sequencing of loci SAG1 and GRA6. Of these 38 isolates, 13 (34. 2%) are clonal Type II strains which can be further divided into two groups at the locus Apico. Two of the 38 isolates have Type II alleles at all loci except a Type I allele at locus L358. One isolate has Type II alleles at all loci except the Type I alleles at loci L358 and Apico. One isolate has Type III alleles at all loci except SAG2, NSAG2 and Apico. One isolate may have a mixed infection. Twenty-one (57.8%) isolates are Type X-like strains. Genotyping and DNA sequence analysis for 16 of these 21 Type X-like isolates at loci SAG1 and GRA6 revealed that there are two different genotypes, including the previously identified Type X (two isolates) and a new genotype named Type A (14 isolates). The results from this study suggest that even though the sea otter’s isolates are genetically diverse, they can be divided into three groups, with two groups closely related to the clonal Type II and Type III lineages, and the other group of Type A-Type X. T. gondii was considered a contributing cause of death in only three of 35 sea otters; these three otters had genotype A (2 otters), and Type II (1 otter), and also had other fatal conditions. Differences in the geographic distribution of different genotypes between California and Washington state were not evident.