Abstract
Domestic animals play a central role in pathogen transmission at the human-wildlife interface. Domestic cats, in particular, are uniquely consequential in disease spillover dynamics due to their global distribution, large, human-subsidized free-roaming populations, and high contact rate with humans, domestic animals, and wildlife. However, the extent to which human ownership and management mitigate this spillover risk remains a key knowledge gap. To address this gap, we conducted a global systematic review and quantitative synthesis of the prevalence and diversity of zoonotic pathogens in indoor-only, outdoor-owned (roaming unsupervised), and unowned (feral or stray) cats. Our dataset comprised 174,064 individuals from 88 countries, representing 124 pathogen species, 97 of which are zoonotic. Using generalized linear models within a Bayesian framework and rarefaction analyses, we show that ownership provides limited protection against zoonoses when owned cats have unsupervised outdoor access. Outdoor-owned cats were 3-5 times more likely to carry zoonotic pathogens than indoor-only cats, and, notably, had infection odds statistically equivalent to those of feral cats, despite receiving presumed veterinary care and feeding. Feral cats carried the highest pathogen diversity, however, outdoor-owned cats still harbour 1.5 times the helminth richness of indoor cats, highlighting their potential as effective bridges for pathogen spillover. With approximately 62% of owned cats roaming freely worldwide, and rates exceeding 90% in some regions, these findings reveal a major yet overlooked route of zoonotic risk. Public health and One Health frameworks have traditionally focused on feral cats; however, our results highlight the need to explicitly incorporate owned outdoor cats into zoonotic disease prevention strategies by restricting unsupervised roaming and promoting responsible ownership practices. Without such integration, current frameworks risk overlooking a pervasive and preventable pathway for pathogen transmission at the human-wildlife-domestic animal interface.