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Understanding Bird Flu: Origins of Bird Flu

Posted on: Wednesday, 23 November 2005, 09:00 CST

Influenza has afflicted human beings for thousands of years, but the vicious strain of bird flu, H5N1, that now threatens a global pandemic has been around for less than 50 years.

The ancient Greek physician Hippocrates, father of the Hippocratic Oath, described cases of human flu in 462 B.C. Major epidemics have occurred about three times in each century, most disastrously in the 1918 "Spanish Flu" that killed an estimated 50 million people.

Flu is caused by a virus _ a microscopic particle so small that it cannot live on its own, but must enter a living cell in order to feed itself and reproduce.

The original home of the flu virus was in migrating waterfowl, like ducks and geese. They have developed a natural immunity to the virus, so they don't get sick. However, they carry the virus around the world, infecting domestic poultry flocks that have no immunity to it.

Over the years, the virus has mutated _ altered its genes _ so that it can infect other animals, like pigs, dogs, horses and humans.

The oldest recorded specimen of the virus was detected in Italy in 1878. It was then called "Fowl Plague," which later was discovered to be the same as the virus infecting humans.

The 1918 pandemic was spawned by a bird flu virus that adapted itself to infect people and spread rapidly. That virus is known as H1N1 after the H1 and N1 genes that give it its destructive power.

Further modifications led to an H2N1 virus that caused a pandemic in 1957, and then an H3N2 strain involved in a major outbreak in 1968.

The first recorded appearance of the H5N1 virus was on a chicken farm in Aberdeen, Scotland, in 1959. It was a relatively mild variety that did little damage at first, but spread to Asia, infected domestic poultry and mutated into a highly lethal form.

H5N1 was detected in domestic geese in southern China in 1996 and then in Hong Kong, where the first reported human fatalities occurred in 1997. Eighteen people were infected and six died, but a mass slaughter of chickens temporarily stamped out the disease.

In 2003, however, H5N1 resurfaced in Hong Kong and South Korea. Since then it has spread to 15 countries in Asia and Eastern Europe. It has sickened more than 120 people and killed 67 of them, a mortality rate of more than 50 percent.

So far, the virus has not developed the ability to pass easily from person to person. Such a mutation could happen at any time, a peril that has caused worldwide alarm.

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(c) 2005, Knight Ridder/Tribune Information Services.

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Source: Knight Ridder Washington Bureau

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