Researchers unlock secrets of 1918 flu pandemic

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Researchers unlock secrets of 1918 flu pandemic

Reuters

Tuesday, 30 December 2008

Researchers have found out what made the 1918 flu pandemic so deadly -- a

group of three genes that lets the virus invade the lungs and cause

pneumonia.

They mixed samples of the 1918 influenza strain with modern seasonal flu

viruses to find the three genes and said their study might help in the

development of new flu drugs.

The discovery, published in Tuesday's issue of the Proceedings of the

National Academy of Sciences, could also point to mutations that might turn

ordinary flu into a dangerous pandemic strain.

Yoshihiro Kawaoka of the University of Wisconsin and colleagues at the

Universities of Kobe and Tokyo in Japan used ferrets, which develop flu in

ways very similar to humans.

Usually flu causes an upper respiratory infection affecting the nose and

throat, as well as so-called systemic illness causing fever, muscle aches

and weakness.

But some people become seriously ill and develop pneumonia. Sometimes

bacteria cause the pneumonia and sometimes flu does it directly.

During pandemics, such as in 1918, a new and more dangerous flu strain

emerges.

" The 1918 influenza pandemic was the most devastating outbreak of infectious

disease in human history, accounting for about 50 million deaths worldwide, "

Kawaoka's team wrote.

It killed 2.5 percent of victims, compared to fewer than 1 percent during

most annual flu epidemics. Autopsies showed many of the victims, often

otherwise healthy young adults, died of severe pneumonia.

" We wanted to know why the 1918 flu caused severe pneumonia, " Kawaoka said

in a statement.

They painstakingly substituted single genes from the 1918 virus into modern

flu viruses and, one after another, they acted like garden-variety flu,

infecting only the upper respiratory tract.

But a complex of three genes helped to make the virus live and reproduce

deep in the lungs.

The three genes -- called PA, PB1, and PB2 -- along with a 1918 version of

the nucleoprotein or NP gene, made modern seasonal flu kill ferrets in much

the same way as the original 1918 flu, Kawaoka's team found.

Most flu experts agree that a pandemic of influenza will almost certainly

strike again. No one knows when or what strain it will be but one big

suspect now is the H5N1 avian influenza virus.

H5N1 is circulating among poultry in Asia, Europe and parts of Africa. It

rarely affects humans but has killed 247 of the 391 people infected since

2003.

A few mutations would make it into a pandemic strain that could kill

millions globally within a few months.

Four licensed drugs can fight flu but the viruses regularly mutate into

resistant forms -- just as bacteria evolve into forms that evade antibiotics.