Why the Spanish Flu Was Able to Kill Healthy WWI Troops

(Library of Congress)

The Wuhan Coronavirus appears to be the first major health crisis of 2020. China's Health Minister reports that the virus is increasing in virulence and people could be infected without knowing.

Fear is spreading across the globe faster than the virus itself.

Little more than a century ago, the world faced a similar situation. As World War I raged in Europe, the Spanish flu rampaged with it -- and across the rest of the planet. By the time the flu disappeared, some 500 million people had been infected and at least 50 million had died, according to the Centers for Disease Control and Prevention.

The 1918-1919 pandemic was the deadliest and most widespread in recorded history.

What was truly remarkable about that virus was that it was able to more easily kill otherwise healthy adults, especially the fighting men in the trenches of the Great War -- more than children or the elderly. Usually, influenza works the other way around.

Much of the virus' spread could be attributed to crowded military encampments and war-related transportation, meaning the war directly affected more than half a billion people around the world.

It's said that, for every American service member killed in the trenches, another 12 fell to disease, much of that caused by the Spanish flu. Influenza and pneumonia killed more Americans during the war than the German military.

Why were able-bodied troops so susceptible to the virus?

According to a 2009 study by Emily Breidbart, then a fourth-year medical student at NYU School of Medicine, the answer is counterintuitive. She says the troops' strong immune systems were to blame.

Influenza is usually killed off long before it enters the lungs, but not so with the Spanish Flu. Instead, the virus made its way into the respiratory system, where it dug in and faced the inevitable onslaught of T-cells sent to kill it by the body's immune system.

The study says people's immune systems went over the top in response to the virus.

"The capillaries surrounding the alveoli dilated and poured out fluid composed of white blood cells, antibodies, and cytokines. Cytokines and enzymes effaced the capillaries. More fluid poured into the lung. The cells lining the alveoli were damaged, and hyaline membranes formed. Surfactant production ceased. The body produced fibrous connective tissue, entangling the lung in debris, fibrin, and collagen... continued exudation of fluid in areas where blocking of smaller bronchi had occurred would produce eventually airless regions."

Army Nurses During the 1918 Spanish Flu Pandemic
Nurses During the 1918 Spanish Flu Pandemic. (Library of Congress)

Essentially, the body would drown itself trying to kill the virus. So the stronger and more able the immune system, the more liquid the body could produce, killing itself faster than someone with a weaker immune response.

Army pathologists have studied remains of soldiers killed by the Spanish flu, buried in the permafrosts of Alaska, and found the signs of this sequence of events in those bodies. The self-destructive behavior is now known as a "cytokine storm."

Doctors have long since learned that previous exposure to flu viruses decreases the effectiveness of new strains on the body. New Army recruits during the Great War were more likely to suffer the effects of the disease and die from it than veterans who had been previously infected with other strains.

But the most vital lessons learned during that long-ago pandemic were the importance of handwashing and vaccines for flu prevention.

-- Blake Stilwell can be reached at blake.stilwell@military.com.

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Military History World War I