Epidemiology of COVID-19 from a ‘One Health’ perspective: stray animals, humans, and wastewater

Abstract SARS-CoV-2 virus, identified in 2019, has demonstrated rapid human-to-human transmission, with a spectrum of clinical manifestations ranging from mild to fatal. Transmission is primarily through respiratory droplets, but evidence suggests a potential spread through contaminated body fluids, including fecal matter, with detectable viral RNA in wastewater. Additionally, both domesticated and wild animals have been infected, raising concerns about reverse spillover events and the emergence of animal-adapted viral variants. This study aimed to assess the correlation between COVID-19 trends in humans, stray cats and dogs, and wastewater viral RNA levels within a One Health framework to enhance pandemic understanding and prediction. We analyzed data from April 2021 to November 2022 in five Northeastern Italian provinces encompassing human infection rates, wastewater viral RNA concentrations, and stray animals’ infection data. The study employed regression models suitable for count data (Poisson and negative binomial) and a Gamma regression model for continuous viral RNA concentration data in wastewater. A marked increase in human cases was noted in later waves compared to the fourth wave (e.g., a 7.5-fold increase during the 7th wave). The prevalence of infection in stray animals remained very low and did not significantly fluctuate between waves. The trends of SARS-CoV-2 RNA in wastewater mirrored the COVID-19 epidemic curve observed in humans. No significant correlation was found between wastewater viral RNA concentrations and stray animal positivity rates. This research did not establish a significant association between human cases, stray animal infections, and wastewater viral RNA levels during the COVID-19 epidemic, also given the limited amount of animal information gathered. Ad-hoc planning of such multidisciplinary, one-health studies is mandatory to exploit the full potential of this approach. Key messages • Human SARS-CoV-2 trends closely mirrored wastewater viral RNA concentrations, confirming the utility of wastewater surveillance in epidemic monitoring. • Multidisciplinary One Health approaches are essential but require ad-hoc planning and sufficient sampling to fully assess interspecies transmission dynamics.