Children of the 70s and 80s will likely remember Oregon Trail, the computer game where the player assumes the role of wagon leader and guides a group of settlers through the pioneer landscape of 19th-century America. You would hunt bison, shoot rabbits, ford rivers and pick up other settlers as you made your way from Missouri to Oregon. But just as you really got into the game, this would happen:
If you are like me, you probably shouted: ‘NOT AGAIN!’
So what exactly is dysentery, and why did you and all your settlers keep dying from it in Oregon Trail?
Dysentery is an intestinal inflammation that causes severe diarrhea, usually characterised by mucus or blood in the feces. Left untreated, the disease can lead to rapid loss of fluids, dehydration, and eventually death.
There are two forms of dysentery. One is caused by a bacterium, the other, an amoeba. The former is the most common in Western Europe and the United States; and is typically spread through contaminated food and water.
Outbreaks of dysentery were more prevalent during war, where the disease spread rampantly because of the unhygienic conditions of the camps. During the Mexican War (1846-48), a staggering 88% of deaths were due to infectious disease, most of those overwhelmingly dysentery. For every man killed in battle, seven died of disease. The American Civil War was no better. You were more likely to die off the battlefield than on it, and dysentery was the primary cause. 
That said, civilians also died of dysentery with some frequency in the 19th century, especially those who were itinerant. Pioneers travelling the Oregon Trail wouldn’t have faired much better than soldiers fighting in war. They would have travelled in large groups—wagon after wagon trailing one another—and their access to clean water and food would have been severely limited. In 1853, one pioneer wrote in her diary: ‘Still in camp, husband and myself being sick (caused, we suppose, by drinking the river water, as it looks like dirty suds than anything else)’.
Diseases such as tuberculosis, flu, measles and smallpox spread like wildfire through their crowded, makeshift camps. Dysentery would have been one of the leading causes of death amongst these pioneers, although it is difficult to determine just how many died from it as medical records were typically not kept.
What we do know is that roughly 20,000 people died travelling the 2,000-mile trail in the 19th century. To put that in perspective: there was an average of ten graves per mile. Burials were often hastily done right in the middle of the trail. This would allow wagons and animals to trample down the grave so that the scent of decomposition was erased and wolves wouldn’t feast on the remains. 
In another diary from the period, one pioneer writes: ‘A grave three feet deep and wide enough to receive the eleven victims [of a massacre] was dug, and the bodies placed in it. Wolves excavated the grave and devoured the remains…[Volunteers] gathered up the bones, placed them in a wagon box, and again buried them.’
So there you have it. Life on the Oregon Trail was just as rough as the computer game would have us believe. Food was scarce. Roads were treacherous. And disease was rampant.
I will never again complain about the inconveniences of air travel.
1.V. J. Cirillo, ‘“More Fatal than Powder and Shot”: Dysentery in the US Army during the Mexican War, 1846-48’ in Perspectives in Biology and Medicine 52(3): pp. 400-13.
2. Statistics cited on National Oregon Trail/California Trail Center.