Cats (Felis catus) are reservoirs of several pathogens that affect humans, including Toxoplasma gondii. Infection of pregnant women with T. gondii can cause ocular and neurological lesions in newborns, and congenital toxoplasmosis has been associated with schizophrenia, epilepsy, movement disorders, and Alzheimer's disease. We compared seroprevalence of T. gondii and risk factors in people on seven islands in Mexico with and without introduced cats to determine the effect of cat eradication and cat density on exposure to T. gondii. Seroprevalence was zero on an island that never had cats and 1.8% on an island where cats were eradicated in 2000. Seroprevalence was significantly higher (12-26%) on the five islands with cats, yet it did not increase across a five-fold range of cat density. Having cats near households, being male and spending time on the mainland were significant risk factors for T. gondii seroprevalence among individuals, whereas eating shellfish was protective. Our results suggest that cats are an important source of T. gondii on islands, and eradicating, but not controlling, introduced cats from islands could benefit human health. Author summary Infection with T. gondii can cause miscarriage or severe ocular and neurological lesions in newborns, systemic disease in immunocompromised individuals, and has been linked to mental disorders and neurodegenerative diseases such as schizophrenia, Alzheimer's and movement disorders in adults. On the majority of islands, introduced cats are the only species capable of maintaining the sexual phase of the life cycle of Toxoplasma gondii. Introduced cats on islands are also responsible for 14% of all bird, mammal and reptile extinctions. Their management, which has been implemented as a biodiversity conservation measure, has the potential to reduce or eliminate the burden of diseases caused by T. gondii in island communities via control of its definitive host. To examine if management of introduced cats could reduce risk of infection with T. gondii, we compared the seroprevalence and risk factors associated with T. gondii exposure in people on seven islands with variation in cat density, including one island in which cats were eradicated in the year 2000, and another island in which cats had never been present. We found that eradication of introduced cats on islands could significantly reduce human risk of exposure to T. gondii. Seroprevalence of T. gondii was zero on the island that never had cats and near zero on the island where cats were eradicated. Furthermore, all island resident children born after cats were eradicated showed no evidence of exposure to the parasite. The odds of seropositivity to T. gondii were nearly five-fold higher in people that had cats near their homes. On islands with cats, we found no association between local cat density and T. gondii seroprevalence, suggesting that complete eradication rather than control of cat population densities is necessary to reduce public health impacts of toxoplasmosis.
