An update on Toxoplasma gondii infections in northern sea otters (Enhydra lutris kenyoni) from Washington State, USA

Authors: VERMA, SHIV - Non ARS Employee; LYNCH, DEANNA - Us Fish And Wildlife Service; KNOWLES, SUSAN - National Wildlife Health Center; CEZAR, CAMILA - Non ARS Employee; Kwok, Oliver; JIANG, TIANTIAN - University Of Tennessee; SU, CHUNLEI - University Of Tennessee; Dubey, Jitender

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2018
Publication Date: 5/26/2018
Citation: Verma, S., Lynch, D., Knowles, S., Cezar, C., Kwok, O.C., Jiang, T., Su, C., Dubey, J.P. 2018. An update on Toxoplasma gondii infections in northern sea otters (Enhydra lutris kenyoni) from Washington State, USA. Veterinary Parasitology. 258:133-137. https://doi.org/10.1016/j.vetpar.2018.05.011
DOI: https://doi.org/10.1016/j.vetpar.2018.05.011

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, abortion in livestock, and contributes to mortality in wildlife. 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 under cooked meat from infected animals and food and water contaminated with oocyst. Why some people become ill and even die from toxoplasmosis whereas others remain asymptomatic is largely unknown. The genetic characteristics of T. gondii strains are considered a factor in the pathogenesis on clinical disease. Toxoplasmosis in marine life is indicative of contamination of seas with oocysts excreted by cats. In the present paper the authors genetically characterized isolates of Toxoplasma obtained by bioassay of sea otter tissues. Results indicated genetic diversity including strains that are prevalent in humans and domestic animals. The results will be useful for parasitologists and biologists.

Technical Abstract: Toxoplasmosis in marine mammals is epidemiologically and clinically important. Toxoplasma gondii antibodies (by modified agglutination test, cut-off =1:25) were detected in serum of 65 of 70 (92.9%) northern sea otters (Enhydra lutris kenyoni) from Washington State, USA. Brains and/or muscles of 44 sea otters were bioassayed in mice (INF-' knock-out [KO], Swiss Webster outbred [SW]) and viable T. gondii was isolated from 22 of 44 (50%); T. gondii strains were lethal to KO mice but not SW mice. These T. gondii isolates were further propagated in cell culture. Multi-locus PCR-RFLP genotyping of cell culture-derived tachyzoites revealed four different genotypes among 22 isolates including ToxoDB PCR-RFLP genotype #5 (14 isolates), #1 (three isolates), #3 (four isolates), and #167 (one isolate). PCR-DNA sequencing based genotyping using polymorphic gene GRA6 revealed one of four different alleles. Among the 14 RFLP genotype #5 strains, 10 have GRA6 sequences that match with the Type A, one match with the Type X, two strains did not generate sequence data, and one strain had double peaks at known polymorphic sites indicating a mixed infection. The seven strains belong to genotypes #1 and #3 all have identical sequences to T. gondii Type II reference isolate ME49. Genotype #167 strain has identical sequence to Type I reference strain. In summary, we observed high seroprevalence, and high rate of isolation of T. gondii from northern sea otters and predominant genotype #5 that has been previously reported a dominant and widespread strain among terrestrial wildlife in North America. GRA6 sequence analysis of the genotype #5 isolates indicated the dominance of Type A lineage in sea otters in Washington State.