More than 20 people returning to the U.S. from Cuba have been infected with a virus transmitted by bugs in recent months, federal health officials said Tuesday. They all had Oropouche virus disease, also known as sloth fever.

None have died, and there is no evidence that it’s spreading in the United States. But officials are warning U.S. doctors to be on the lookout for the infection in travelers coming from Cuba and South America.

Here’s a look at the illness and what sparked the…