With 46 U.S. cases and alarming signs of the virus crossing species, experts warn of unpredictable risks if human-to-human ...

Known to spread from person to person ... letter genetic mutations indicative of the ongoing battle between the human immune system and the virus — a pattern that would be unlikely to appear ...

Almost from the beginning of the spread of H5N1 bird flu among farms and ranches in the U.S. earlier this year, experts and ...