EndocrinologyStudy Suggests H1N1 Virus More Dangerous Than Suspected
A new, highly detailed study of the H1N1 flu virus shows that
the pathogen is more virulent than previously thought.
Writing in a fast-tracked report published in the
journal Nature, an international team of researchers led by University of
Wisconsin-Madison virologist Yoshihiro Kawaoka provides a detailed
portrait of the pandemic virus and its pathogenic qualities.
In contrast with run-of-the-mill seasonal flu viruses, the H1N1virus
exhibits an ability to infect cells deep in the lungs, where it can cause
pneumonia and, in severe cases, death. Seasonal viruses typically infect
only cells in the upper respiratory system.
"There is a misunderstanding about this virus," says Kawaoka, a professor
of pathobiological sciences at the UW-Madison School of Veterinary
Medicine and a leading authority on influenza. "People think this pathogen
may be similar to seasonal influenza. This study shows that is not the
case. There is clear evidence the virus is different than seasonal
influenza."
The ability to infect the lungs, notes Kawaoka, is a quality frighteningly
similar to those of other pandemic viruses, notably the 1918 virus, which
killed tens of millions of people at the tail end of World War I. There
are likely other similarities to the 1918 virus, says Kawaoka, as the
study also showed that people born before 1918 harbor antibodies that
protect against the new H1N1 virus.
And it is possible, he adds, that the virus could become even more
pathogenic as the current pandemic runs its course and the virus evolves
to acquire new features. It is now flu season in the world"s southern
hemisphere, and the virus is expected to return in force to the northern
hemisphere during the fall and winter flu season.
To assess the pathogenic nature of the H1N1 virus, Kawaoka and his
colleagues infected different groups of mice, ferrets and non-human
primates - all widely accepted models for studies of influenza - with the
pandemic virus and a seasonal flu virus. They found that the H1N1 virus
replicates much more efficiently in the respiratory system than seasonal
flu and causes severe lesions in the lungs similar to those caused by
other more virulent types of pandemic flu.
"When we conducted the experiments in ferrets and monkeys, the seasonal
virus did not replicate in the lungs," Kawaoka explains. "The H1N1 virus
replicates significantly better in the lungs."
The new study was conducted with samples of the virus obtained from
patients in California, Wisconsin, the Netherlands and Japan.
The new Nature report also assessed the immune response of different
groups to the new virus. The most intriguing finding, according to
Kawaoka, is that those people exposed to the 1918 virus, all of whom are
now in advanced old age, have antibodies that neutralize the H1N1 virus.
"The people who have high antibody titers are the people born before
1918," he notes.
Kawaoka says that while finding the H1N1 virus to be a more serious
pathogen than previously reported is worrisome, the new study also
indicates that existing and experimental antiviral drugs can form an
effective first line of defense against the virus and slow its spread.
There are currently three approved antiviral compounds, according to
Kawaoka, whose team tested the efficacy of two of those compounds and the
two experimental antiviral drugs in mice. "The existing and experimental
drugs work well in animal models, suggesting they will work in humans,"
Kawaoka says.
Antiviral drugs are viewed as a first line of defense, as the development
and production of mass quantities of vaccines take months at best.
In addition to his appointment at UW-Madison, Kawaoka also is a professor
at the University of Tokyo. The new study was funded by grants from the
U.S. National Institutes of Health, and the Japanese Ministry of
Education, Culture, Sports, Science and Technology.
University of Wisconsin-Madison