What is so worrying about avian flu?
The current concern focuses on a type known as H5N1, first discovered in terns in 1961. It is astonishingly lethal in chickens and extremely contagious: Just 1 gram of fecal material can infect 40 million other birds. In 1997, H5N1 proved capable of infecting humans near chickens and has proved fatal in about half of all cases, a strikingly high fatality rate.
