Avian influenza, also known as bird flu, is a viral infectious disease that typically affects only birds.
Avian influenza viruses are highly species-specific, but in rare cases, they can cross the species barrier and infect humans. Since the discovery in 1997 that humans can also contract avian influenza in Hong Kong, this disease has drawn significant attention from health organizations worldwide. In fact, sporadic outbreaks of this disease have long occurred in Asia, but beginning in December 2003, avian influenza broke out severely in several East Asian countries—primarily Vietnam, South Korea, and Thailand—resulting in the deaths of numerous patients in Vietnam. As of mid-2005, the epidemic showed no signs of abating and continued to spread. Currently, cases have been reported as far away as Eastern European countries.

Avian influenza can be transmitted to many animal species, including birds, pigs, horses, seals, whales, and humans; however, wild birds act as asymptomatic carriers, transmitting the virus to more susceptible domestic poultry. Among birds, transmission occurs primarily through respiratory and fecal-oral routes; there is currently no evidence that the virus can survive in cooked meat. The virus first infects the digestive tract of birds, replicating within the epithelial cells of the small intestine and eventually being shed in feces. The clinical symptoms of avian influenza vary widely among animals, but highly pathogenic strains can be fatal within a matter of days.

Symptoms of avian influenza in humans are similar to those of other forms of influenza, including fever, cough, sore throat, muscle aches, and conjunctivitis. In severe cases, respiratory problems and pneumonia may develop, which can be life-threatening.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News