Honolulu Health Chronicles: International Study of H1N1 Pandemic Virus Shows Great Danger

The filamentous shape of H1N1 shown budding from infected cells
Image: courtesy Yoshihiro Kawaoka – University of Wisconsin

The prestigious science journal Nature felt so strongly about the importance of a new international collaborative analysis of what H1N1 pandemic flu virus really is, that they took the exceptional measure of fast track publication of the news. Headed up by University of Wisconsin virologist Yoshihiro Kawaoka the international study is a broad based statement about the danger of H1N1 and not just another opinion. Dr. Kawaoka provides a scientific picture of the pandemic virus and its pathogenic qualities.

In contrast with run-of-the-mill seasonal flu viruses, the H1N1 virus 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."

In 1918 the virus was able to infect the lungs. That is a key factor in how dangerous the virus can be to worldwide health. Kawaoka compares the current H1NI structure to that to the other pandemic viruses, like the 1918 virus which devastated the world near 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.

Mice, ferrets and other primates were the study animals that Kawaoka and his team infected ­ with the H1N1 pandemic virus and a seasonal flu virus. The H1N1 samples were obtained from patients in California, Wisconsin, Japan and the Netherlands.

The H1N1 virus reproduced with much greater speed and efficiency in the lungs than the selected seasonal flu virus. Not only that but H1N1 caused the severe lesions in the lungs that are caused by the seriously 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."

Dr. Kawaoka said that the most notable finding is that people who were alive in 1918 and exposed to that virus carry antibodies that neutralize the H1N1 virus. "The people who have high antibody titers are the people born before 1918," he notes.

Kawaoka is encouraged that his research shows 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.

While the world appears to have moved past a large death toll in the H1N1 pandemic, it may have been a closer call than we thought.