Genetic researchers are making ground-breaking—and possibly life-saving—discoveries about the 1918 flu pandemic.

WASHINGTON (Reuters) — 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. ...

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. ...

“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. ...

“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.