Rats sold in the markets and restaurants of Southeast Asia harbour multiple coronaviruses, BBC News reports, citing a study.
The proportion of positives increased as live animals were moved from "field to fork", suggesting they were picking up viruses in the process.
The strains detected are different from Covid-19 and are not thought to be dangerous to human health.
But scientists have long warned that the wildlife trade can be an incubator for disease.
The mixing of multiple coronaviruses, and their apparent amplification along the supply chain into restaurants, suggests "maximal risk for end consumers", said a team of researchers from the US and Vietnam.
The origins of the current pandemic are thought to lie in the wildlife trade, with the disease emerging in bats and jumping to people via another, as yet unidentified, species.
The new findings, regarded as preliminary, relate to rats, but may apply to other wildlife, such as civets and pangolins, which are also collected, transported and confined in large numbers.
