Researchers have recently discovered the cause which had led to the death of so many people sickened by the flu in 1918. They discovered that there existed three types of genes that let the influenza virus spread to the lungs and thus, to cause pneumonia.

The scientists found about this after they had mixed samples of the influenza virus strain from 1918 with the modern strains of flu viruses. This way, the discovered the existence of the three genes and added that this new findings could help in the improvement of the drugs designed to cure the flu.

The findings were published on Tuesday in the “Proceeding of the National Academy of Sciences” and they could also point toward the discovery of new mutations which might turn the common flu into a dangerous pandemic virus.

The study was developed by Yoshihiro Kawaoka of the University of Wisconsin and colleagues at the Universities of Kobe and Tokyo in Japan. They used ferrets as to develop the flu in ways alike to the ones in humans. Commonly, the flu develops an upper respiratory infection which affects the throat and nose. Besides these, the flu causes also fever, weakness and aches in the muscles.

Yet, there are some people who can also develop pneumonia either caused by the bacteria or by the flu directly. During the pandemics, like the one in 1918, usually a more dangerous strain develops, which can sometimes be lethal. The team wrote that the influenza pandemic from 1918 was the most terrible outbreak “of infectious disease in human history.” At that time, about 50 million people lost their lives.