Montezuma's revenge is a slang or colloquialism for diarrhea that has been contracted while in Mexico or in other countries in Latin America by tourists and people who are not locals. The term "Montezuma's revenge" is reference to the event in history when the local Latin American people were conquered by the Europeans. The term describes the idea wherein the diarrhea and the discomfort associated with it is seenas the revenge taken by the local gods. These are the gods that the local population worshipped before the Europeans christianized the region.
But the meaning of Montezuma's revenge should not be taken literally, the diarrhea is not an ailment sent by gods but the body's reaction to bacteria and parasites that are ingested from contaminated water sources and food. "Montezuma's revenge" -- that is, diarrhea -- is encountered not just in Latin American countries but also in other countries all over the world where water is not treated properly to eliminate these bacterial and parasitic agents. Additionally, food that is washed improperly can also bring on Montezuma's revenge.
Generally, Montezuma's revenge is transient, in that it will go away after suffering from a bout of sickness. Some of the more effective treatments include taking bismuth sulfate otherwise commercially known as Pepto Bismol. But children who experience diarrhea and fever should not be given this treatment because it has salicylic acid as one of its active ingredients, and this is a substance that is linked to the development of Reye's syndrome.