Mounting preliminary evidence suggests the "swine flu" is a relatively mild flu strain

Scientists see this flu strain as relatively mild

LA Times
By Karen Kaplan and Alan Zarembo
April 30, 2009

As the World Health Organization raised its infectious disease alert level Wednesday and health officials confirmed the first death linked to swine flu inside U.S. borders, scientists studying the virus are coming to the consensus that this hybrid strain of influenza -- at least in its current form -- isn't shaping up to be as fatal as the strains that caused some previous pandemics.

In fact, the current outbreak of the H1N1 virus, which emerged in San Diego and southern Mexico late last month, may not even do as much damage as the run-of-the-mill flu outbreaks that occur each winter without much fanfare.

"Let's not lose track of the fact that the normal seasonal influenza is a huge public health problem that kills tens of thousands of people in the U.S. alone and hundreds of thousands around the world," said Dr. Christopher Olsen, a molecular virologist who studies swine flu at the University of Wisconsin School of Veterinary Medicine in Madison.

His remarks Wednesday came the same day Texas authorities announced that a nearly 2-year-old boy with the virus had died in a Houston hospital Monday.

"Any time someone dies, it's heartbreaking for their families and friends," Olsen said. "But we do need to keep this in perspective."

Flu viruses are known to be notoriously unpredictable, and this strain could mutate at any point -- becoming either more benign or dangerously severe. But mounting preliminary evidence from genetics labs, epidemiology models and simple mathematics suggests that the worst-case scenarios are likely to be avoided in the current outbreak.

"This virus doesn't have anywhere near the capacity to kill like the 1918 virus," which claimed an estimated 50 million victims worldwide, said Richard Webby, a leading influenza virologist at St. Jude Children's Research Hospital in Memphis, Tenn.

When the current virus was first identified, the similarities between it and the 1918 flu seemed ominous.

Both arose in the spring at the tail end of the flu season. Both seemed to strike people who were young and healthy instead of the elderly and infants. Both were H1N1 strains, so called because they had the same types of two key proteins that are largely responsible for a virus' ability to infect and spread.

The Centers for Disease Control and Prevention and the National Institutes of Health published genetic sequence data Monday morning of flu samples isolated from patients in California and Texas, and thousands of scientists immediately began downloading the information. Comparisons to known killers -- such as the 1918 strain and the highly lethal H5N1 avian virus -- have since provided welcome news.

"There are certain characteristics, molecular signatures, which this virus lacks," said Peter Palese, a microbiologist and influenza expert at Mt. Sinai Medical Center in New York. In particular, the swine flu lacks an amino acid that appears to increase the number of virus particles in the lungs and make the disease more deadly.

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Just because the virus is being identified in a growing number of places — including Austria, Canada, Germany, Israel, New Zealand, Spain and Britain — doesn’t mean it’s spreading particularly quickly, Olsen said.

“You don’t ever find anything that you don’t look for,” he said. “Now that diagnostic laboratories and physicians and other healthcare workers know to look for it, perhaps it’s not surprising that you’re going to see additional cases identified.”

And a pandemic doesn’t necessarily have a high fatality rate. Even in Mexico, the fatalities may simply reflect that hundreds of thousands of people have been infected. Since the symptoms of swine flu are identical to those of a normal flu, there’s no way to know how many cases have evaded government health officials, St. Jude’s Webby said.

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