With cold and flu season approaching, it’s worth knowing about another virus out there—albeit extremely rare: bird flu. Like the regular flu, bird flu virus symptoms include fever, cough and a sore throat.

Several labs will work with federal health authorities to develop a test for avian influenza, as the number of human cases rise across the country.

A close contact of someone with bird flu became ill on the same day, the C.D.C. reported. But the second person was not tested, and the cause of the illness is unknown.

Federal officials are still trying to determine how a Missouri resident with no known exposure to bird flu, contracted the virus.

The case is concerning because it's the first human case this year not tied to a known exposure to animals. Before now, all positive cases came after a person came into contact with infected dairy cows or poultry.

Avian flu in dairy cows could stick around on US farms forever, and is raising the risk of outbreaks in mammals—including humans—around the world.

Genetic analysis of a bird flu virus detected in a person in Missouri who didn’t previously have contact with animals offers more details on the case, but experts say there isn’t substantial evidence