Experts unearth history of pandemic flu viruses

By Tan Ee Lyn

HONG KONG (Reuters) - Flu viruses that sparked the three worst pandemics in the last century circulated in their near-complete forms for years before the catastrophes occurred, researchers in Hong Kong and the United States have found.

The H1N1 virus that sparked the Spanish flu of 1918-1919 circulated in swine and humans well before the pandemic started, and it did not come directly from birds as previously thought, they added. Instead, it was probably generated by genetic exchanges between flu viruses from swine and humans.

This contrasts sharply with previous studies which suggested that the H1N1 virus of 1918 was a mutant that jumped direct from birds to human and ended up killing as many as 50 million people.

The findings are considered important because of the lack of studies of the virus in animals before the current outbreak of H1N1. Through understanding the natural history of viruses, monitoring of current viruses can be fine-tuned, the team from the University of Hong Kong and St Jude Children's Hospital in the United States wrote.

Published in the Proceedings of the National Academy of Sciences, the study also involved two other pandemic viruses

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the H2N2 responsible for the Asian flu of 1957, and the H3N2 which sparked the Hong Kong flu of 1968.

Guan Yi, microbiologist at the University of Hong Kong and member of the research team, said the viruses of 1918 and 1957 went through at least two rounds of reassortments before the pandemics occurred. Reassortments happen when flu viruses swap genetic material, which happens when an animal or person is infected with two strains at the same time.