Study Suggests H1N1 Virus More Dangerous than Suspected

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.