Bird Flu Alarm

Understanding Avian Influenza

History of Human infection with avian influenza viruses

History of Human infection with avian influenza viruses

The first documented infection of humans with an avian influenza virus was in Hong Kong in 1997, when the H5N1 strain caused severe respiratory disease in 18 humans, of whom 6 died. This outbreak coincided with an epidemic of highly pathogenic avian influenza, caused by the same strain, in Hong Kong's poultry population.

Investigation showed that close contact with live infected poultry was the source of human infection - virus jumped directly from birds to humans. Limited transmission to health care workers occurred, but did not cause severe disease.

Rapid destruction - within three days - of Hong Kong's entire poultry population, estimated at around 1.5 million birds, reduced opportunities for further direct transmission to humans, and may have averted a pandemic.

That event alarmed public health authorities, as it was the first time that an avian influenza virus was transmitted directly to humans and caused severe illness with high death rates. Iin February 2003, an outbreak of H5N1 avian influenza in Hong Kong caused 2 cases and 1 death in members of a family who had recently travelled to southern China. Another child in the family died during that visit, but the cause of death is not known.

Two other avian influenza viruses havecaused illness in humans. An outbreak of highly pathogenic H7N7 avian influenza began in the Netherlands in February 2003, causing the death of a vet two months later, and mild illness in 83 other people. Mild cases of avian influenza H9N2 in children occurred in Hong Kong in 1999 (two cases) and in mid-December 2003 (one case). H9N2 is not highly pathogenic in birds.

The most recent cause for alarm occurred in January 2004, when laboratory tests confirmed the presence of H5N1 avian influenza virus in human cases of severe respiratory disease in the northern part of Viet Nam.