Bird flu typically spreads among birds, but there have been recent outbreaks among cattle in the U.S., and one Texas man contracted the virus from sick cows. Here’s why so many experts are worried about a possible new pandemic.

As of Friday, all that was known about the Missouri case was that the individual was infected with an H5 virus. The CDC was still working to try to figure out the neuraminidase of the virus, the N of its name. Sometimes that isn’t possible, for instance if there isn’t a lot of virus in the sample from the patient.

A hospitalized patient in Missouri was infected with bird flu despite having had no known contact with dairy cows or other animals associated with an ongoing outbreak, health officials said Friday.