SARS-CoV-2 infections among animals in US zoological institutions resulted primarily from human-to-animal transmission without evidence of sustained evolution in animals (2020-2023).

Abstract

OBJECTIVE: We conducted a retrospective observational study to investigate exposure history, clinical signs, and onward transmission of animals infected with SARS-CoV-2 in US zoological institutions. METHODS: We analyzed animal surveillance data collected through voluntary national surveillance during 2020 to 2023, including a descriptive epidemiologic analysis of surveillance data, comparative genomic analysis of SARS-CoV-2 sequences from zoo animals and the US human population, and comparison of impacts at the human-animal interface for a subset of zoological institutions (n = 12) with a SARS-CoV-2 animal outbreak. RESULTS: During 2020 to 2023, 170 animals in zoological institutions were confirmed positive for SARS-CoV-2. These animals consisted of 13 species in 28 US jurisdictions. Of affected animals, 72.4% presented with clinical signs, most commonly cough (60.0%). The likely source of SARS-CoV-2 in animals was a known infected caretaker in 44.7% of cases. Some zoological institutions participated in an in-depth analysis of outbreaks; these institutions implemented an average of 48.7 and 52.9 of 88 recommended biosecurity practices in the month before and after an outbreak, respectively, in their facility. CONCLUSIONS: Zoological institutions were a high-risk setting for SARS-CoV-2 transmission via spill-back from people to animals. Genomic analysis supported that zoo animals became infected with SARS-CoV-2 variants circulating in humans at the time, with no evidence of significant viral evolution in zoo populations. CLINICAL RELEVANCE: Mitigating emerging infectious disease threats in these facilities is critical for protecting vulnerable animal populations and public health.