Is it time for Americans to worry about bird flu?

H5N1 AVIAN INFLUENZA, MORE COMMONLY KNOWN AS bird flu, has infected more than 100 million birds in the U.S. and almost 500 dairy-cattle herds across 15 states.

- JAMIE DUCHARME

The virus has popped up in mammals including elephant seals, goats, foxes, and house cats. But despite its prolific spread among animals, federal health authorities maintain that the risk to the U.S. public remains low. There have been only 46 confirmed human cases in the U.S. during the current outbreak. All but one of those people had a known exposure to affected poultry or cattle, according to the U.S. Centers for Disease Control and Prevention (CDC), and all of their illnesses were mild. The CDC says there is no proof that the virus is spreading from person to person at this time.

Recent news, however, has some people feeling uneasy. On Nov. 12, Canadian health officials announced that an otherwise healthy teenager there who caught bird flu from an unknown source is in critical condition, underscoring the illness's possible severity—and its sometimes mysterious spread.