Disease-causing bacteria carry on a complex, hidden interaction with the human body. Emigrants along the trail were exposed to a variety of unsanitary conditions where bacteria could thrive and be easily picked up. Numerous bacteria cause diarrhea and probably most emigrants suffered this affliction to a lesser or greater degree. Severe diarrhea can kill, but it apparently benefits both the bacteria and the infected. Diarrhea spreads the bacteria to new human hosts, and it flushes the bacteria quickly from the human's body.
The intestines are exposed constantly to pathogenic (disease-causing) bacteria. Each has a unique and very specific way of changing human cells. Stomach acid can kill bacteria in small amounts, but if the bacteria can enter the small intestines in significant numbers, illness results. Dr. Alessio Fasano, University of Maryland School of Medicine, in a Salt Lake Tribune article, Jan. 9, 1997, described nine diarrhea-causing bacteria and how they operate in the small intestine:
Emigrants heading to the gold fields in California in 1849 took too many supplies and discarded large amounts along the trail. Emigration in 1850 was twice as large. Travelers listened to reports filtering back to the east and overcompensated by taking too little provisions. Cholera struck with a vengeance, claiming more lives this year than any other during the emigration period. According to California Trail historian, George Stewart, The stretch of trail from Mary's sink (western end of the Humboldt River) to the Carson River in 1850 claimed 10,000 animals. As many as 3,000 wagons were abandoned, also.