The authorities quickly tested the birds and moved into high gear, killing 800,000 chickens, disposing of the carcasses and cleaning the farm to stop the potential spread to other chicken farms. But they were also concerned for humans.

They tested the birds and sequenced the virus, determining that it was the H5N8 strain of avian flu, highly dangerous to both wild and domestic birds. It is established in Asia and has been increasingly causing deadly outbreaks in birds in Europe. H5N8 viruses have infected some poultry flocks in the United States, but the viruses come from a different though related lineage of virus, distinct from the current H5N8 viruses in Asia and Europe. Flu viruses combine and mutate frequently in unpredictable ways.