Spillback

When the World Health Organization declared COVID-19 a pandemic on March 11, 2020, humans had been the only species with reported cases of the disease. While early genetic analyses pointed to horseshoe bats as the evolutionary hosts of SARS-CoV-2, the virus that causes COVID-19, no reports had yet surfaced indicating it could be transmitted from humans to other animal species. Less than two weeks later, a report from Belgium marked the first infection in a domestic cat – presumably by its owner. Summer 2020 saw news of COVID-19 outbreaks and subsequent cullings in mink farms across Europe and fears of similar calls for culling in North America. Humans and other animals on and around mink farms tested positive, raising questions about the potential for a secondary wildlife reservoir of COVID-19. That is, the virus could infect and establish a transmission cycle in a different species than the one in which it originated. Researchers have documented this phenomenon of human-...