In year three of the pandemic, scientists have confirmed that the virus believed to have first spilled over to humans from bats or possibly pangolins has already spread to at least 20 other animal species, including big cats, ferrets, North American white-tailed deer and great apes. To date, incidents of animals infecting humans are rare. Only three species — hamsters in Hong Kong, mink in the Netherlands and, possibly, also white-tailed deer in the United States and Canada — have transmitted a mutated, albeit mostly benign, version of the virus back to humans. But those cases are spurring concern.

The search for infected animals in Texas — led by Texas A&M University in conjunction with the U.S. Centers for Disease Control and Prevention — is part of a scattered but growing global effort to monitor pets, livestock and wildlife for new, potentially more dangerous coronavirus variants and stop them from wreaking havoc on humans.

The World Health Organization warned in March that animal reservoirs could lead to “potential acceleration of virus evolution” and new variants. The agency noted the large numbers of infected animals, and it urged countries to increase their monitoring of mammalian species for SARS-CoV-2 and suspend the sale of live, wild mammals in food markets as an emergency measure. The CDC this year also endorsed efforts to track the virus in animals, even as it described the risk of transmission to humans as “low.”