Parasite and pathogen prevalence in our closest animal companions is determined by accessibility of sanitation services

Despite the critical role parasites play in ecosystem functioning and their considerable influence on human society, little is known about their variations in abundance on a global scale. This gap in knowledge is amplified by a lack of holistic understanding on how the abundance of parasites of wildlife and humans varies across environmental and socioeconomic gradients, despite a need to integrate study of parasites across social and environmental spheres. Free-roaming companion animals (e.g., domestic cats (Felis catus) and dogs (Canis lupus familiaris)) share pathogens and have frequent contact with humans and wildlife. Thus, they are an effective model to understand how parasite and pathogen prevalence of humans and wildlife varies across environmental and socioeconomic gradients. Through a global systematic review and analysis of socioeconomic and environmental variables, including per capita GDP, income disparity, sanitation, biodiversity, island habitation, and latitude, we find that sanitation and island habitation best explained free-roaming companion animal parasite and pathogen prevalence. Sanitation was significantly associated with parasite and pathogen prevalence in free-roaming companion animals, such that for every 10% increase in the proportion of the human population with improved sanitation access, parasite and pathogen prevalence in free-roaming companion animals decreased by 12% (5-19%, 95% C.L.; p = 0.0023). Since companion animals share many parasites with humans and wildlife, these results suggest that actionable interventions to improve sanitation access could reduce parasite and pathogen exposure risks from companion animals to humans and wildlife. Significance StatementIn addition to playing a critical role in ecosystem functioning, parasites also influence human health, behavior, and society. Further, parasites are also impacted by human activities, as much as by ecological phenomena in natural environments. Despite these dualities, little is known about their variations in abundance on a global scale across environmental and socioeconomic gradients. Using free-roaming companion animals (e.g., domestic cats (Felis catus) and dogs (Canis lupus familiaris)) as a model system, we find that access to safely managed sanitation services is strongly associated with parasite and pathogen prevalence. This finding underscores improvements to sanitation as an actionable One Health intervention that could reduce parasite and pathogen exposure risks from companion animals to humans and wildlife.