THEY ARE ADORABLE ANIMALS with little furry faces, and they’re playful and cuddly. But ferrets can catch and spread disease to humans, which is one reason many jurisdictions in the U.S. have banned them as pets. In an infectious disease lab, however, that same viral vulnerability can make the common ferret an asset — perhaps now more than ever. In the worldwide race to develop treatments and vaccines for Covid-19, researchers need animals in which to observe the illness and challenge it with interventions. And it turns out that ferrets are vulnerable to the same respiratory infections that impact humans — including SARS-CoV-2, the virus that causes Covid-19. A study published earlier this month concluded that ferrets can carry and pass on the disease, and get sick with it as well, developing fevers and losing their appetites.