Yellow fever was an ancient scourge of 18th and 19th century battlefields, causing more fatalities than bullets, cannon balls, or swords. Introduced to the tropical Americas by the slave trade, the dreadful disease struck military camps without warning, decimating entire armies.
Victims developed chills, fever, and muscle aches, followed by liver failure, which produced jaundice (yellowing of the skin and eyes). Some victims bled from the nose and gums, and internally into the stomach, resulting in black vomit, giving the disease its Spanish name, vomito negro.
No one knew what caused yellow fever. They knew it was not contagious between individuals, and people commonly believed it was transmitted by fomites (contaminated objects), such as clothing and blankets. There was no treatment for yellow fever other than supportive care, and as many as half of its victims died.
Yellow Fever and The Spanish-American War
The effect of yellow fever on armies was clear during the Spanish-American War in 1898. That brief four-month war and the occupation of Cuba afterward cost nearly 3,000 American lives. Of those, less than 400 died in combat. The rest died of disease, including 2,000 soldiers who died from yellow fever alone.
The United States military was well aware of the yellow fever threat in Cuba, particularly during the summer months, when the spread of the disease was at its worst. Nevertheless, war fever drove the U.S. to invade Cuba in late June, at the height of the yellow fever season.
After declaring war on Spain in April 1898, the War Department ordered the formation of regiments from southern states where yellow fever was endemic. It was thought these soldiers would be immune to the disease, and the regiments were called “the Immunes.” Immune, however, they were not: eventually, more than a third of the soldiers in one black Immune regiment died from yellow fever or malaria.
The first yellow fever cases among American troops appeared on July 6. Within weeks, hundreds of soldiers were sick with the black vomit or malaria. Spanish troops fared no better: out of an army of 230,000 soldiers, only 55,000 troops were healthy enough to fight. Disease, said the American commander, Major General William Shafter, was a “thousand times harder to stand up against than the missiles of the enemy.”