Cats have been introduced to approximately 179,000 islands, and co-occur with people in approximately 560 of them. Islands with abundant human subsidies can maintain high densities of introduced cats. This has resulted in substantial damage to populations of native species and may also favor opportunities for pathogen transmission to humans. Human health is emerging as an important component in the debate about feral cat population control. Cats are reservoirs of zoonotic pathogens, including Toxoplasma gondii. Toxoplasmosis can cause miscarriages or severe ocular and neurological lesions in newborns, systemic disease in immunocompromised individuals, and is associated to psychiatric diseases and behavioral changes. Holding high concentrations of feral cats in islands can lead to high concentrations of T. gondii in the environment, leading to increased exposure in humans. Islands provide an ideal setting to control or potentially eliminate local sources of T. gondiithrough cat population control or eradication programs. Understanding how seroprevalence of toxoplasmosis in humans responds to feral cat density can better inform decisions about cat population management. We conducted a prospective serological study in two neighboring islands off the Pacific coast of Baja California, Mexico: Cedros, which harbors 0.9 cats/inhabitant, and Natividad, where cats were eradicated in 2000.
Results/Conclusions
We obtained blood samples from 420 inhabitants to estimate and compare crude and age-specific seroprevalence of toxoplasmosis in both islands. Crude seroprevalence of toxoplasmosis was significantly lower in Natividad (2.13%) compared to Cedros (13.5%) (p < 0.001). Age-specific seroprevalence was also significantly lower in Natividad in the 10-15 and 50-60 age groups (p < 0.001), and we only found seropositive cases in Natividad in the 20-30 and 30-40 age groups. Our results suggest that feral cats may be an important source of T. gondii exposure in these two Mexican islands, and that cat eradication may be acting as a protective agent against local exposure in Natividad. However, to better understand how toxoplasmosis responds to cat density and potentially estimate the contribution of local cats to parasite exposure we will expand this study to the remaining four inhabited islands located in the Mexican Pacific (Guadalupe, San Marcos, Santa Margarita and Maria Madre), which have similar climatic and socioeconomic conditions, but harbor feral cat colonies at different densities.