Scientists who synthesised two genes from the virus that caused the 1918 Spanish influenza pandemic said on Thursday they have new clues about what made it so deadly.

Between 20 million and 50 million people worldwide died in the 1918-1919 pandemic, the deadliest in the past century. By unravelling the secrets of the virus, researchers hope to improve methods to spot the next potential flu pandemic, which some scientists believe is overdue.

“We found that just one gene called HA, haemagglutinin, is sufficient to make a benign virus pathogenic,” said Yoshihiro Kawaoka, of the University of Wisconsin-Madison and the University of Tokyo.

Scientists suspect the 1918 virus originated in birds and leapt to humans. The spread of bird flu in Asia has raised fears that the strain could mutate and become highly infectious in humans.

“At this point we don’t know why Spanish virus HA makes a benign virus highly pathogenic but by studying this HA we will know,” Kawaoka, who headed the research team, told Reuters.

“We can use that information to predict, when a new virus appears, whether it is pathogenic and can cause a devastating outbreak or not.”

In research reported in the latest edition of the science journal Nature, Kawaoka and his colleagues used genetic material of the 1918 virus taken from the lung of a person who died from the illness.

They synthesised HA and another gene from the 1918 virus, inserted them into benign viruses and tested the engineered viruses on mice. The mice quickly became ill and suffered symptoms similar to those of patients who died in the pandemic.

“One of the hallmarks of the 1918 Spanish flu is haemorrhage in the lungs. That is what we found in the lungs of the mice,” he said.

Although other genes may be involved, the researchers believe HA is important.

“Limited genes can make a benign virus pathogenic and the influenza virus is known to change easily, so we need to watch these viruses in nature,” Kawaoka added.

SOURCE: Nature 2004.