Influenza is a viral infection of the nose and throat that typically causes fever, headache, muscle aches and weakness. Sometimes pneumonia complicates the flu. The cause can be bacterial or the virus itself. In a typical season, flu mortality is well below 1%.
In 1918, an extraordinary number of flu victims developed pneumonia. Mortality ran 400% higher than usual.
In fact, “The 1918 influenza pandemic was the most devastating outbreak of infectious disease in human history, accounting for about 50 million deaths worldwide,” according Yoshihiro Kawaoka and colleagues from the University of Wisconsin and the Universities of Kobe and Tokyo.
Now these scientists think they’ve discovered what triggered the pandemic.
The team isolated genes one-by-one from the 1918 strain, substituted them into the modern flu virus and then infected ferrets, which develop flu a lot like humans do.
Time after time the ferrets developed normal flu until the scientists used a 3-gene combination called PA, PB1, and PB2 (along with a 1918 version of the nucleoprotein or NP gene).
This combination enabled the flu virus to invade the lungs, causing pneumonia and death. The team has published its findings in the Proceedings of the National Academy of Sciences.
Most experts believe there will be another flu pandemic someday. No one knows when or which strain will cause it, but the H5N1 avian influenza virus that currently circulates among birds and domestic poultry in Asia, Africa and Europe remains a likely suspect.
The current strain of Avian flu rarely infects humans but when it does, it kills. More than 60% of the 391 people infected so far have died.
A few mutations that increase its attack rate in humans would transform H5N1 into a monster that could kill millions in months.