H5N1: Prelude to a pandemic?

In the current epidemic, two influenza subtypes have proved especially dangerous - H7N7, which sickened poultry workers in the Netherlands, and H5N1, which has been responsible for the majority of human and avian deaths in Asia. Of these, H5N1 is of particular concern for several reasons:


Direct transmission. H5N1 became the first known bird flu strain to jump directly from birds to people when it surfaced in Hong Kong in 1997. It has since infected people in many countries. Other strains have caused illness in humans, but none is as severe as H5N1.

Virulence. The virus is especially lethal, killing close to 100 percent of susceptible birds and more than half of infected people. Birds that do survive can shed the virus for at least 10 days, greatly increasing the flu's spread.

Rapid spread. Since 2003, hundreds of millions of birds have died, a loss that's ecologically and economically devastating. It's also alarming from a public health standpoint - widespread infections among birds may lead to more human disease