for National Geographic News
A global influenza pandemic, like the "Spanish flu" of 1918, could leave tens of millions dead. Many experts insist that the world is unprepared, and overdue, for just such a catastrophe.
Pandemics are disease outbreaks that occur over a wide area and sicken or kill very high percentages of the affected populations. These outbreaks often occur when viruses mutate into new forms that the human immune system cannot fight.
The leading contender for the next pandemic is H5N1, a strain of avian influenza, or "bird flu." The virus is found primarily in domestic and wild birds but also in mammals such as cats and pigs (see "Cats Can Catch and Spread Bird Flu, Study Says"). When H5N1 appeared in 1997 it killed six people in Hong Kong and southern China.
Since 2003 more than 50 people have died from H5N1 in Thailand, Vietnam, and Cambodia. Experts say those deaths are a drop in the bucket, compared to the predicted devastation should H5N1 mutate into an easily transmitted form.
"The situation right now with H5N1 is very similar to what we saw in 1918," said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota in Minneapolis.
The virus behind the influenza pandemic of 1918called H1N1killed an estimated 20 to 40 million people worldwide. (See "Disastrous 1918 Flu Linked to Birds, Study Says.")
"Not all influenza strains are created equal, and it's more than just idle speculation that an H5N1 pandemic could mirror that of 1918," Osterholm noted.
Osterholm is one of many experts who address the threat of avian flu and the next pandemic in this week's issue of the journal Nature.
Fortunately H5N1 is not yet spreading easily from person to person. But history suggests that the strain, or one that is similarly dangerous, will likely acquire that ability in the not too distant future.
Each of at least three known pandemics prior to 1918 had a global death rate equal to or higher than that of the 1918 outbreak. And in 1968 some 750,000 people died during a pandemic of the relatively mild H3N2 avian flu virus.
The human toll of a new, highly contagious avian flu could be shocking. Some experts estimate that 20 percent of the globe's population could fall ill and tens of millions could die.
The health threat would likely set in motion further calamities. Reductions in foreign trade and travel are probable, because governments would attempt to lock down their borders to prevent the spread of the virus, experts predict.
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