The origin and control of pandemic influenza.

Perspectives in Biology and Medicine, 43, 2 • Winter 2000 | 173 In 1918 an epidemic of influenza killed 20 million people worldwide. Spanish flu, as it was called, was a horrific disease. The flu would start with headaches, muscular pain, and fever. These would be rapidly followed by vomiting, dizziness, labored breathing, and profuse sweating. Sometimes purple blisters would appear on the skin, and often blood would spurt out of the nose from hemorrhages in the lungs. Some of the victims of this dreadful, sudden, and unexpected illness went into violent fits of coughing. Death often followed, sometimes only hours after the first symptoms appeared. Influenza viruses infect a number of different animals, and some of these viruses can cause very serious disease indeed, particularly in domesticated chickens and turkeys. Avian influenza viruses sometimes rapidly kill these birds, with 100 percent mortality, and the symptoms resemble, at least to some extent, those of the Spanish flu in 1918. You can imagine, therefore, the concern felt when, in late 1997, a virulent bird flu virus, which had never before been seen in man, started infecting and killing people in Hong Kong [1]. This virus, designated H5N1, killed six of the 18 people it infected. The virus seems to have been transmitted to people from infected chickens in the live bird markets, but so far there has been no evidence that the virus had learned how to spread from person to person. But there is also no reason to suppose that this might not happen, some time in the future. Killing off all the chickens in Hong Kong seems to have stopped the epidemic, at least for the time being. What could be done to control such a virulent influenza virus, which, if it took off, would spread through