A Qualitative Framework for Ranking the Relative Likelihood of SARS-CoV-2 Transmission Between People and Felids at Zoological Interfaces

SARS-CoV-2 transmission between humans and animals is an important One Health concern, particularly in settings where close human–animal interactions are difficult to avoid. We developed and applied a qualitative likelihood ranking framework for SARS-CoV-2 transmission between people and captive lions (Panthera leo) in an urban zoological setting. Following a structured review, scenario trees were constructed to rank direct and indirect transmission pathways using five domains: activity duration, proximity and frequency, SARS-CoV-2 survival on fomites, and environmental conditions. The framework was applied to a case study of a lion exhibit at an urban zoo in Australia. Pathway ranking depended on the combined effects of baseline exposure attributes and subsequent modifiers reflecting exposure frequency and level of natural disinfection. Although direct pathways, such as veterinary procedures, had the highest likelihood of transmission, they were differentiated by interaction duration and proximity, with frequency modification distinguishing rare, high-intensity interactions from repeated lower-intensity activities. Therefore, routine husbandry or visitor-associated exposures could increase in relative importance. Environmental modification further differentiated pathway likelihood, in particular due to solar exposure and temperature. The framework provides a transparent, practical approach for ranking transmission likelihood when data are scarce, supports consistent prioritisation of biosecurity resources, and is applicable to other emerging infectious disease threats in zoological settings.