Avian influenza

Definition

Avian influenza is flu infection in birds. The disease is of concern to humans, who have no immunity against it. The virus that causes this infection in birds can mutate (change) to easily infect humans. Such mutation can start a deadly worldwide epidemic.

Alternative Names

Bird flu; H5N1

Causes

Historically, avian influenza viruses infected pigs and mixed with pig influenza viruses. The viruses exchanged genetic information, which led to the formation of a new virus. This new virus could then infect humans and easily spread from person to person. Previous flu pandemics (worldwide epidemics) have started this way.

The first avian influenza virus to infect humans directly occurred in Hong Kong in 1997, during an avian flu epidemic on the island. This outbreak was linked to chickens and classified as avian influenza A (H5N1).

Since the Hong Kong outbreak, the bird flu virus has spread across Asia, and in October 2005 was discovered in poultry in Turkey and Romania. So far, hundreds of people have been infected by H5N1. Many people have died.

The wider the area over which the avian flu virus spreads, the greater the chances of a worldwide outbreak. There is tremendous concern that H5N1 poses an enormous pandemic threat.

Farmers and other people working with poultry, as well as travelers visiting affected countries, have a higher risk for getting the bird flu. Handling an infected bird can cause infection. People who eat raw or undercooked poultry meat are also at an increased risk for avian influenza. Highly infective avian flu viruses, such as H5N1, have been shown to survive in the environment for long periods of time, and infection may be spread simply by touching contaminated surfaces. Birds who recover from the flu can continue to shed the virus in their feces and saliva for as long as 10 days.

Health care workers and household contacts of patients with avian influenza may also be at an increased risk of the bird flu.

References

US Food and Drug Administration. FDA Approves First U.S. Vaccine for Humans Against the Avian Influenza Virus H5N1. Rockville, MD: National Press Office; April 17, 2007. Release P07-68

US Centers for Disease Control and Prevention. New Laboratory Assay for Diagnostic Testing of Avian Influenza A/H5 (Asian Lineage). MMWR. February 3, 2006/55(Early Release);1.

World Health Organization. Cumulative number of confirmed human cases of avian influenza A/(H5N1) reported to WHO. Geneva, Switzerland: World Health Organization; 2006.

Beigel JH, Farrar J, Han AM, et al. Avian Influenza A (H5N1) Infection in Humans. N Engl J Med. 2005;353:1374-85.