MILWAUKEE – An international team of scientists led by a University of Wisconsin-Madison virologist has produced a highly detailed portrait of the swine flu virus that has killed 211 people in the U.S., suggesting it is more virulent than previously thought and contradicting assertions the virus appears similar to seasonal flu.
What makes the 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 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.”
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 the 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 percent of swine flu cases are resulting in death, a mortality rate that suggests the virus is of mild to moderate virulence. In fact, he 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.