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).

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. 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. 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. 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. Mitigating emerging infectious disease threats in these facilities is critical for protecting vulnerable animal populations and public health.