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How the bird flu virus is spread

Influenza viruses can originate both in humans and in birds, and both can be harbored in the trachea's of pigs. When growing together in the pig tracheas, the avian strains and human strains can and do intermix to form new strains, which then can be potentially virulent for humans. Unlike typical influenza viruses, avian flu viruses attack receptors in the lower respiratory tract as well as throughout the body, causing a more virulent form of disease, with a high rate of fatality in humans.

New strains of avian influenza often emerge in Southeast Asia, due to agricultural practices where birds, swine, and humans exist in close proximity. Prior to 1997, bird influenza was thought to exist only in birds. In that year, however, the first 18 cases of avian influenza in humans were detected during a poultry influenza outbreak. Up to 10 per cent of poultry workers showed past infection with the virus.

Between 2003 and 2007, cases of avian influenza continued to emerge, spread from viruses endemic to poultry and ducks. Since February 2006, cases have spread far beyond Southeast Asia, where the viruses have been found in migratory wild birds and poultry in Turkey, Africa, Europe, India, and Israel.

More than 350 cases of avian influenza in humans have been reported by the World Health Organization, with more than 60 per cent of cases being fatal. As they infect humans, the viruses continue to change and mutate.

Further transmission to cats and zoo animals has occurred, presumably through the feeding of infected poultry products and carcasses. There is one fatal case reported in a dog. However, there are no cases reported where humans have contracted the virus from pets or zoo animals.

While most of the infections in people have occurred outside the United States, human to human spread is possible, and bird to human spread, especially from migratory birds, continues to be a risk. People who handle birds, veterinarians, farmers, meat processing workers, swine workers and poultry workers are at highest risk of contracting avian influenza.

Control of the spread of avian influenza has been attempted through the destruction of infected poultry, with limited success. Infected poultry should never be fed to other animals, as that can be a mode of transmission of the virus. Continued spread of the disease through migratory birds remains a difficult problem to control. Vaccines are being developed which may be helpful to prevent the spread in higher risk populations.

Source: Up to Date

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