A World Health Organization scientist said Covid-19 comes from bats and can infect cats and ferrets, but more research is needed into the suspected animal link to the disease.

The novel coronavirus comes from a group of viruses that originate or spread in bats, and it’s still unclear what animal may have transmitted the disease to humans, Peter Ben Embarek, a WHO expert in animal diseases that jump to humans, said Friday in a briefing with reporters.

The virus probably arrived in humans through contact with animals raised for food supply, though scientists have yet to determine which species, he said. Studies have shown that cats and ferrets are susceptible to Covid-19, and dogs to a lesser extent, he said, adding that it’s important to find out which animals can get it to avoid creating a “reservoir” in another species.

Questions about the origin of Sars-CoV2, the virus that has caused the pandemic, have burned hotter since U.S. President Donald Trump suggested that it came from a lab in China. Scientists who have studied the issue maintain that the virus originated in an animal, and probably entered the human population in November.

The first human cases were detected in and around Wuhan, and most people had contact with the animal market, though not all, Ben Embarek said. The WHO intended to spend more time investigating the virus’s animal origin on an earlier mission to China, Ben Embarek has said. The lockdown of Wuhan, the region in central China where the pandemic originated, made that impractical, he said.

Trump has doubled down on claims that the Chinese mistakenly released the virus from the laboratory as the outbreak in the U.S. has grown to become the world’s largest and deadliest. Chinese officials have said that the U.S. has no evidence to back up those claims and called the allegations a blame game.