How far "bird flu" virus has traveled down the evolutionary path to becoming a pandemic virus is unknown. Nor is it certain that the much-feared strain will ever acquire all the genetic features necessary for rapid, worldwide spread. Nevertheless, the similarities between the Spanish flu virus of 1918 and the H5N1 strain slowly spreading through Asia provide unusually concrete evidence of how dangerous the newer virus is. -- Changes Cited in Bird Flu Virus, The Washington Post, October 6, 2005
After a lethal bird flu virus emerged in Asia, U.S. officials launched an intense effort to build new defenses against a pandemic, including replacing an antiquated vaccine system, which depends on millions of chicken eggs.
Track the latest developments in the spread of the deadly H5N1 influenza virus.
What is bird flu? Avian influenza, or bird flu, is a virus that is highly contagious among wild birds and often fatal to domesticated birds and poultry. The H5N1 strain was first detected in humans in 1997 and has killed 60 people in Southeast Asia since 2003.
How do humans get bird flu? The virus is spread through contact with infected birds or contaminated surfaces. However, risk of infection in humans is low and person-to-person transmission is rare.
What is the pandemic threat? Scientists worry the H5N1 virus will mutate and become more easily spread from person to person, spurring a pandemic.
More than 200 million domestic birds have been killed. Ninety-eight people have died. Scientists believe the virus could evolve into a global influenza epidemic. But they cannot predict when, or if, that will occur.