High prevalence and diversity of Toxoplasma gondii DNA in feral cat feces from coastal California.

Toxoplasma gondii is a zoonotic parasite that can cause severe morbidity and mortality in warm-blooded animals, including marine mammals such as sea otters. Free-ranging cats can shed environmentally resistant T. gondii oocysts in their feces, which are transported through rain-driven runoff from land to sea. Despite their large population sizes and ability to contribute to environmental oocyst contamination, there are limited studies on T. gondii oocyst shedding by free-ranging cats. We aimed to determine the frequency and genotypes of T. gondii oocysts shed by free-ranging domestic cats in central coastal California and evaluate whether genotypes present in feces are similar to those identified in sea otters that died from fatal toxoplasmosis. We utilized a longitudinal field study of four free-ranging cat colonies to assess oocyst shedding prevalence using microscopy and molecular testing with polymerase chain reaction (PCR). T. gondii DNA was confirmed with primers targeting the ITS1 locus and positive samples were genotyped at the B1 locus. While oocysts were not visualized using microscopy (0/404), we detected T. gondii DNA in 25.9% (94/362) of fecal samples. We genotyped 27 samples at the B1 locus and characterized 13 of these samples at one to three additional loci using multi locus sequence typing (MLST). Parasite DNA detection was significantly higher during the wet season (16.3%, 59/362) compared to the dry season (9.7%; 35/362), suggesting seasonal variation in T. gondii DNA presence in feces. High diversity of T. gondii strains was characterized at the B1 locus, including non-archetypal strains previously associated with sea otter mortalities. Free-ranging cats may thus play an important role in the transmission of virulent T. gondii genotypes that cause morbidity and mortality in marine wildlife. Management of free-ranging cat colonies could reduce environmental contamination with oocysts and subsequent T. gondii infection in endangered marine mammals and people. Author summary: Toxoplasma gondii is a parasite that can cause severe disease and death in warm-blooded animals such as humans and sea otters. Feral cats can release T. gondii oocysts, or environmentally resistant 'eggs', in their feces. These oocysts can be transported by surface runoff after rainfall and go on to contaminate bodies of water. Oocyst shedding from feral cats is not well understood, and whether they shed specific types of T. gondii that have been found in sea otters that died from toxoplasmosis is not known. We aimed to determine how often feral cats in central coastal California shed T. gondii oocysts and identify types of the parasite in feces. Although we did not see oocysts, 25.9% of samples tested positive for T. gondii DNA. Parasite DNA was more common during the wet vs. dry season. There were diverse T. gondii types found in feral cat feces, including types that were previously found in sea otters that died from toxoplasmosis. Future management of feral cats could reduce environmental contamination and in turn, T. gondii infections in sea otters and humans. [ABSTRACT FROM AUTHOR]

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