In May 1997, a three-year-old boy complaining of cough and fever was admitted to a Hong Kong hospital. During the next several days, the child’s lungs began to fill with fluid, impairing his breathing. Frantic doctors administered large doses of antibiotics and put him on a ventilator. But before the week was out, the child had died.

Doctors were at a loss to explain what had killed the boy. Was it a new lethal strain of bacteria, or was it something viral? Scientists ultimately identified a virus in the child’s respiratory fluid, but the bewilderment of the scientific community persisted; the virus, H5N1—named for particular protein markers found on the organism’s outer shell—had historically been observed only in birds. This was the first time the world witnessed a human death from the avian influenza virus.

Was the May 1997 case a fluke? Doctors and scientists around the world hoped so. That very same December, however, seventeen additional people in Hong Kong contracted the virus, resulting in five deaths. Under pressure from global public health officials, the Chinese government culled all 1.5 million birds from the farm systems and markets around Hong Kong.

The bird flu as we know it today had arrived, but few really noticed. After the 1997 outbreak had been successfully contained, bird flu was once again forgotten. In the last year, however, an outbreak of bird-flu resulting in scores of fatalities has forced governments, policy makers, and thousands of scientists beyond China to begin work to prevent what could be the fiercest pandemic in nearly a century.

To most of us, the flu is a nuisance, something that can be eliminated with a simple shot every year. But the virus that surfaced in Hong Kong eight years ago is of a far different breed. Avian influenza is an infectious disease in birds caused by the type A class of influenza viruses. Transmission may occur when humans come in contact with infected poultry or with contaminated surfaces containing the saliva, nasal secretions, or feces of infected birds. For victims of this rarer, more virulent type of flu, the prognosis ranges from mild illness to highly pathogenic, contagious disease with mortality rates approaching 100%.