Spanish flu
Main article: 1918 flu pandemic
The Spanish flu, also known as la grippe, La Gripe Española, or La Pesadilla, was an unusually severe and deadly strain of swine influenza, a viral infectious disease, that killed some 50 to 100 million people worldwide over about a year in 1918 and 1919. It is thought to be one of the deadliest pandemics in human history.
The 1918 flu caused an unusual number of deaths, possibly due to it causing a cytokine storm in the body.[6][7] (The current H5N1 bird flu, also an Influenza A virus, has a similar effect.)[8] The Spanish flu virus infected lung cells, leading to overstimulation of the immune system via release of cytokines into the lung tissue. This leads to extensive leukocyte migration towards the lungs, causing destruction of lung tissue and secretion of liquid into the organ. This makes it difficult for the patient to breathe. In contrast to other pandemics, which mostly kill the old and the very young, the 1918 pandemic killed unusual numbers of young adults, which may have been due to their healthy immune systems mounting a too-strong and damaging response to the infection.[9]
The term "Spanish" flu was coined because Spain was at the time the only European country where the press were printing reports of the outbreak, which had killed thousands in the armies fighting World War I. Other countries suppressed the news in order to protect morale.[10]