War and Disease: Half the Horsemen

War and disease are the peanut butter and jelly of destruction, together making up half of the horsemen of the Apocalypse. Wherever war goes disease is apt to follow. In fact, historically, more soldiers have died due to disease than at the hands of their human enemies. Although the advent of greater prevention and treatment techniques has quelled the epidemics of the past in recent conflicts, the relationship between combat and disease remains strong. Modern militaries have not only failed to eradicate infectious disease, they have also, much to everyone’s terror, honed the devastating power of pathogens into potential weapons of mass destruction.

Death toll

The conditions of war are ideal for the spread of disease. Training camps, barracks, and refugee camps bring together large groups of people from disparate regions, potentially harboring different infectious agents. The stress, famine and water shortages that occupy war zones along with armed forces suppress the immune systems of soldiers and civilians, leaving them more vulnerable to the attack of pathogens. The unsanitary living conditions that many are forced to endure also foster disease spread7.

Because of its rapid spread among troops, disease was responsible for the majority of deaths in combat zones until the 20th century2,4. The ratio of deaths due to disease and those caused by conflict were truly staggering, getting as high as 7:1 for American troops in the Mexican War. The first war where both armies suffered greater casualities from battle death than from disease was the Russo-Japanese war of 19044. Prior to 1918, the majority of the noncombat deaths (deaths caused by anything other than wounds sustained in combat) in the American armed forces were due to disease2. Infectious diseases, such as dysentery, cholera, typhus, malaria and smallpox, were the most common illnesses to afflict soldiers. The rampages of these epidemics had wide-ranging effects; they not only reduced the fighting ability of the troops, they also impacted the leadership of commanding officers2.

Some things just go together.

The development of vaccines and antibiotics dramatically altered the impact of disease on society generally, including in war. In World War II, mass immunizations kept the spread of diseases such as tetanus (a major illness in WWI), and smallpox, exceptionally low compared to previous conflicts. The mass production of penicillin made bacterial illnesses, like typhus, treatable for the first time. While these improvements curtailed the mortality from the common ailments of war, infectious disease continues to afflict servicemen and women. The US forces lost 9 million man-days of active duty to malaria in WWII between 1942 and 1945, and it, along with other vector-borne diseases, continue to affect US soldiers2,5.

Disease as a weapon

The use of biological weapons, the weaponization of disease, is likely nearly as ancient as warfare itself. The Romans described attempting to introduce a man-made malady of bubonic plague and smallpox to enemy soldiers. European and American military commanders intentionally exposed Native Americans to smallpox1. And biological weapons have continued to be used in the modern era; in the 1930s and 1940s, Japanese forces used the plague and other bacterial agents against the Chinese3. In the 20th century, there were 100 confirmed cases of “illicit use of biological agents”, ranging from personal attacks to national terrorism, and as of 1995, 17 countries were suspected of developing biological weapons6.

Despite the fact that so many nations have experimented with biological weapons, there is widespread repugnance at their use. The public aversion probably reflects a major downside of biological weaponry: they are alive (or in the case of viruses, life-like). Inert arms can be targeted on a specific population, and their impact can be controlled. Biological weapons are unpredictable; there is no way to ensure that they will only affect the enemy. Disease doesn’t respect national borders, and will not limit itself to the destruction of combatants. There is no reason to assume that a weaponized pathogen wouldn’t turn on the nation that deployed it8.

All of these complications lead to the conclusion that biological weapons are a catastrophically bad idea. Most governments seem to agree with that, and international treaties, such as the 1972 Biological Weapons Convention, seek to codify that belief. Unfortunately, these agreements have not stopped several countries from continuing work on biological weapons (even some who’ve signed them). Consequently, many countries have sought preventative measures, setting up defensive research and testing programs, and extensive monitoring systems, which may also cause accidental outbreaks. While these efforts are critical in the suppression of biological weapons, we need to fight fire with fire. To stave off the threat of biological weaponry, we need to cultivate our abhorrence of it. Our greatest protection against biological weapons is our own revulsion.


1. Appel, JM. (2009). Is all fair in biological warfare? The controversy over genetically engineered biological weapons. Journal of Medical Ethics, 35(7): 429-432.

2. Cirillo, VJ. (2008). Two faces of death: Fatalities from disease and combat in America’s principal wars, 1775 to present. Perspectives in Biology and Medicine, 51(1): 121-133.

3. Cole, LA. (1996). The specter of biological weapons. Scientific American, December: 60-65.

4. Councell, CE. (1941). War and infectious disease. Public Health Reports, 56(12): 547-573.

5. Goldrick, BA. (2004). Emerging infections: Another hazard of war: Infectious diseases. The American Journal of Nursing, 104(12): 64-66.

6. Kortepeter, MG, & GW Parker. (1999). Potential biological weapons threats. Emerging Infectious Diseases, 5(4):523-527.

7. Peterson, RKD. (1995). Insects, disease, and military history. American Entomologist, 147-160.

8. Steinbruner, JD. (1997). Biological weapons: A plague upon all houses. Foreign Policy, 109: 85-96.

Image source: http://en.wikipedia.org/wiki/Four_Horsemen_of_the_Apocalypse

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Suzi Claflin

I am a postdoctoral fellow studying chronic disease epidemiology.

5 thoughts on “War and Disease: Half the Horsemen”

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