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How Bird Flu Works


Avian Flu H5N1
Avian flu H5N1 has become common in Asian poultry. Officials believe open-air poultry markets lead to the spread of the disease.
Avian flu H5N1 has become common in Asian poultry. Officials believe open-air poultry markets lead to the spread of the disease.

In 1997, health officials in Hong Kong reported a virulent strain of avian flu. For the first time, it appeared that the virus moved directly from birds to people instead of moving through a second species. The virus caused typical flu symptoms, and it also lead to eye infections, pneumonia and acute respiratory distress. Tests confirmed that this strain of the virus, influenza A H5N1, was completely new to humans.

Eighteen people infected with the virus were hospitalized, and six of them died. The Hong Kong government, alarmed at the potential threat of a pandemic, took drastic steps. In about three days, the government destroyed about 1.5 million birds, the country's entire poultry population. Although this measure sounds extreme, many health experts believe that Hong Kong's actions prevented an influenza pandemic.

Photo courtesy MorgueFile                              Ducks can be asymptomatic carriers of the H5N1 virus.
Photo courtesy MorgueFile Ducks can be asymptomatic carriers of the H5N1 virus.

The H5N1 influenza strain appeared to lay dormant until 2003. Then, government officials in Vietnam and Thailand began to report infections in people and birds. Relatively few people contracted the illness, and most who did had extended direct contact with infected birds. In December of 2004, the disease spread to people in Indonesia and Cambodia. About half of the people who contracted the virus died.

At the same time, agriculture officials reported extensive infections in domestic birds. Approximately 100 million birds died in Asia in 2003 and early 2004, either as a result of the disease or as part of efforts to stop its spread. Major outbreaks continue to occur throughout several Asian countries. In October of 2005, the disease spread to Eastern Europe, likely due to migrating birds. By the following January, several people in Turkey had contracted the disease, most likely from contact with dead birds. Health officials found Nigerian birds infected with the disease in February of 2006.

As of October of 2005, the disease is endemic in Cambodia, China, Indonesia, Thailand and Vietnam [Source: CDC]. Visitors to any of these areas should avoid contact with wild or domestic birds and should stay away from poultry farms and open-air markets that sell live poultry.