Linking conservation biology and epidemiology through the Toxoplasma-cat-wild birds triangle.

Shared pathogens can overpower species barriers connecting wildlife, domestic animals and humans, sometimes compromising biodiversity conservation and animal and human health. This case is best represented by Toxoplasma gondii. This zoonotic protozoan depends on felids as definitive hosts and can infect all warm-blooded species which act as intermediate hosts. Through oocyst shedding, cats and other felids cause environmental contamination facilitating the infection of other vertebrates. This parasite threatens biodiversity conservation causing disease and mortality in birds; wildlife and domestic animal health where it is a significant cause of abortions; and public health through water or vegetables contaminated with oocysts or via raw meat from infected animals. In a One-Health context, the complex drivers of pathogen emergence are best evaluated through cross-disciplinary research. We used camera trapping, environmental DNA, serology and public health data to explore the links between domestic cats, biodiversity, and T. gondii in wildlife and in humans. The study was conducted across 18 study sites in the Iberian Peninsula representing a gradient of urbanization. We found that urbanization increases T. gondii infections in wildlife and in humans while reducing bird diversity, mainly through the presence of unconfined domestic cats. Cat presence was associated with human toxoplasmosis and with T. gondii antibody prevalence in wild boar. Cat presence was also linked with a lower detection of vulnerable bird species. These findings confirm domestic cat presence as a risk factor that amplifies anthropogenic environmental modifications, resulting in consequences not only for the ecosystem but also for animal and human health. This approach represents progress in One Health research by integrating zoonotic disease surveillance and biodiversity monitoring. This could be applied to other pathogens and systems.