H5N1 bird flu virus is the sort of virus under discussion this week in Bethesda, Md. How animal viruses can acquire the ability to jump into humans and quickly move from person to person is exactly the question that some researchers are trying to answer by manipulating pathogens in the lab.

H5N1 bird flu virus is the sort of virus under discussion this week in Bethesda, Md. How animal viruses can acquire the ability to jump into humans and quickly move from person to person is exactly the question that some researchers are trying to answer by manipulating pathogens in the lab.