New flu resembles feared 1918 virus

By Maggie Fox, Health and Science Editor

WASHINGTON (Reuters) - The new H1N1 influenza virus bears a disturbing resemblance to the virus strain that caused the 1918 flu pandemic, with a greater ability to infect the lungs than common seasonal flu viruses, researchers reported on Monday.

Tests in several animals confirmed other studies that have shown the new swine flu strain can spread beyond the upper respiratory tract to go deep into the lungs -- making it more likely to cause pneumonia, the international team said.

In addition, they found that people who survived the 1918 pandemic seem to have extra immune protection against the virus, again confirming the work of other researchers.

"When we conducted the experiments in ferrets and monkeys, the seasonal virus did not replicate in the lungs," said Yoshihiro Kawaoka of the University of Wisconsin, who led the study.

The H1N1 virus replicates significantly better in the lungs."

The new swine flu virus has caused the first pandemic of the 21st century, infecting more than a million people, according to estimates, and killing at least 500. The World Health Organisation says it is causing mostly moderate disease but Kawaoka said that does not mean it is like seasonal flu.

"There is a misunderstanding about this virus," he said in a statement. "There is clear evidence the virus is different than seasonal influenza."

Writing in the journal Nature, Kawaoka and colleagues noted that the ability to infect the lungs is a characteristic of other pandemic viruses, especially the 1918 virus, which is estimated to have killed between 40 million and 100 million people.