No evidence of Toxoplasma Gondii infection in urban and rural squirrels

Abstract

Wildlife in cities can act as reservoirs for parasites that can infect domestic pets and have implications for human health. For example, the Coccidian parasite Toxoplasma gondii can infect all mammalian species, with felids acting as the only definitive hosts. Rodents, such as squirrels, could play an important role in urban infection dynamics of T. gondii, as squirrels occur at higher densities in cities than in natural environments and regularly share their territories with cats. In urban and suburban areas squirrels can encounter infectious oocysts shed in cat feces in contaminated soil or in the food they eat. They are also preyed upon by cats making them a potentially important species for completing the T. gondii life cycle in cities. We hypothesized that due to increased exposure to cats, urban squirrels would be more susceptible to T. gondii infection relative to squirrels in more natural areas. We investigated this using molecular and serological methods on samples collected from American red squirrels (Tamiasciurus hudsonicus), eastern grey squirrels (Sciurus carolinensis), northern flying squirrels (Glaucomys sabrinus), and least chipmunks (Tamias minimus) in and around the city of Winnipeg, Manitoba, Canada. We tested a total of 230 tissue samples from 46 squirrels for T. gondii DNA using quantitative PCR and supplemented these data with analyses of 13 serum samples from grey squirrels (Sciurus carolinensis) testing for T. gondii antibodies by indirect ELISA. We found no evidence of T. gondii infection in any squirrel. This suggests that squirrels may not be important intermediate hosts of T. gondii in cities and do not need to be considered as sources of infection to cats.