Study: Swine Flu More Virulent Than Regular Flu
An international team of scientists led by a University of Wisconsin-Madison virologist has produced a highly detailed portrait of the new swine flu virus that has killed 211 people in the U.S., suggesting it is more virulent than previously thought and contradicting assertions that the virus appears similar to seasonal flu.
What makes the new H1N1 virus different and more deadly than common seasonal influenza is its ability to infect cells deep in the lungs where it can cause scarring and pneumonia, according to a fast-tracked report Monday in the journal Nature.
The new study sends "a very clear message" that doctors and patients in the U.S. must adopt a new approach to influenza, said UW virologist Yoshihiro Kawaoka, who led the group of more than 50 scientists in Madison and Japan who are studying the H1N1 virus.
"Seeing physicians early and getting anti-viral drugs is not common practice," Kawaoka said. "That has to be changed."
The study also found that people exposed to the deadly 1918 influenza appear to have antibodies that neutralize swine flu. This may explain why relatively few elderly people have died in the recent H1N1 outbreak. So far, the virus has killed four people in Wisconsin, including two children.
Kawaoka and his colleagues infected mice, ferrets, pigs and nonhuman primates with the H1N1 virus, using samples of the virus obtained from patients in California, Wisconsin, the Netherlands and Japan. They found that while seasonal flu usually infects only cells in the upper respiratory system - the nose, throat and larynx - swine flu was able to take root and grow in the lungs.
In mice with swine flu, the lungs essentially filled with fluid until they could not take in oxygen and the animals died. Other animals in the study did not die from the swine flu.
"There is a misunderstanding about this virus," Kawaoka said. "People think this pathogen may be similar to seasonal influenza. This study shows that is not the case."
"This swine influenza," he added, "is more (virulent) than seasonal influenza. That is for sure."
However, some experts remain unconvinced that the H1N1 virus is substantially more deadly than seasonal flu.
"The real issue with any infectious disease is how it's spreading, not how it looks in the laboratory," said Marc Siegel, a national flu expert and author of the book "Bird Flu: Everything You Need to Know About the Next Pandemic."
Siegel said 0.2% of swine flu cases are resulting in death, a mortality rate that suggests the virus is of mild to moderate virulence. In fact, Siegel said the mortality rate is probably even lower since most swine flu deaths are being reported, but many nonfatal cases are likely going unreported.
"I think there's a few million cases and the deaths are still in the hundreds," Siegel said.
Kelly Henrickson, a professor of pediatrics and microbiology at the Medical College of Wisconsin, called the study "critical and extremely valuable" but cautioned that work in animal models is not always an accurate predictor of what will happen in humans.
"Ultimately the experiment that matters is in people," said Henrickson, who practices at Children's Hospital of Wisconsin.
He said the number of new swine flu cases in Milwaukee has dropped off rapidly in recent weeks, but health officials are concerned about what will happen in the fall, when children return to school.
"It's either going to start coming back two weeks into school or it won't, and if it doesn't, all bets are off," he said.
Henrickson and others have been studying the flu outbreak in Milwaukee, where more cases have been reported than in many entire states. He said H1N1 is more concentrated than the seasonal influenza.
Many researchers are now studying the genetic evolution of the H1N1 strain. The hope is that learning how the virus evolves will help health care officials plan for it better and produce a more effective vaccine.
Scientists studying the virus in animals are likely to continue searching for specific markers of virulence.
"The 1918 virus had several virulence factors," Siegel said, "including the ability to destroy the mitochondria of cells," an ability that H1N1 has yet to demonstrate. The mitochondria generate energy for cells; when they're destroyed, the cells die.
As seen in the Journal Sentinel.
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