Bird flu (also called
avian influenza) is an infection caused by
avian flu viruses. These viruses occur naturally among wild birds worldwide, who carry the viruses in their intestines but usually do not get sick from them. However, bird flu is highly contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and even kill them.
Infection with bird flu in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The "low pathogenic" form may go undetected, and usually causes only mild
bird flu symptoms (such as ruffled feathers and a drop in egg production). However, the "highly pathogenic" form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs, and it has a mortality rate that can reach 90 percent to 100 percent, often within 48 hours.
Bird flu viruses do not usually infect humans, but more than 100 confirmed cases have occurred since 1997. Most cases of bird flu in humans have resulted from direct or close contact with infected poultry (domesticated chickens, ducks, and turkeys) or surfaces contaminated with secretions and excretions from infected birds. The spread of bird flu viruses from an ill person to another person has been reported only rarely, and transmission has not been observed to continue beyond one person.
What Is Bird Flu and Why the Concern?
There are two main risks to human health from bird flu. The first is the risk of direct infection when the virus passes from the infected bird to humans, sometimes resulting in severe disease. The greater concern with bird flu, however, is that given enough opportunities, the bird flu will change into a form that is highly infectious for humans and that spreads easily from person to person. If this happens, a
pandemic flu outbreak could occur.
(Click Bird Flu for more information about bird flu is and why it is a concern for humans.)
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