1918 flu pandemic
Emergency hospital in Kansas during influenza epidemic of 1918. Otis Historical Archives Nat'l Museum of Health & Medicine

A pandemic similar to the 1918 Spanish flu virus that killed an estimated 40 million people could happen again, scientists have warned.

Researchers say current circulating bird flu viruses have all the genetic ingredients needed for the emergence of a virus similar to the 1918 flu.

An international team of scientists led by Yoshihiro Kawaoka of the University of Wisconsin-Madison discovered eight genes from influenza viruses found in wild ducks that have "remarkable genetic similarities" to the genes that made the 1918 pandemic flu virus.

Published in the journal Cell Host and Microbe, findings showed there are gene pools in nature that could cause a "severe pandemic in the future".

Using reverse genetic methods, the team generated a virus that differed from the 1918 virus by just 3% in terms of its amino acids that make the virus proteins. The virus created was more pathogenic in mice and ferrets than normal bird flu viruses, but not as pathogenic as the 1918 virus.

The team then worked out how many changes would be needed for the flu virus found in wild ducks to become transmissible in ferrets – a model for influenza transmission.

They found seven transmissions in three viral genes allowed the flu to transmit as efficiently as the 1918 virus, meaning all the ingredients are there for a potentially deadly and pandemic pathogen.

Kawaoka said knowing what genes to look for will help to predict the risk of an emerging strain and better allow scientists to find ways to stop it.

"The point of the study was to assess the risk of avian viruses currently circulating in nature," Kawaoka said. "We found genes in avian influenza viruses quite closely related to the 1918 virus and, to evaluate the pandemic potential should such a 1918-like avian virus emerge, identified changes that enabled it to transmit in ferrets.

"With each study, we learn more about the key features that enable an avian influenza virus to adapt to mammals and become transmissible. Eventually, we hope to be able to reliably identify viruses with significant pandemic potential so we can focus preparedness efforts appropriately."