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UW study of swine flu virus finds it more virulent than regular flu

By Mark Johnson of the Journal Sentinel
Posted: July 13, 2009
http://www.jsonline.com/features/health/50634332.html

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.”

Some skepticism

However, some experts remain unconvinced that the H1N1 virus is substantially more deadly than seasonal flu.

Fall awaited

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.