What causes travelers’ diarrhea? Travelers’ diarrhea is usually caused by bacteria, viruses, or parasites that get into food or water. The most common causes are bacteria, especially certain types of Escherichia coli, or E. coli.
Travelers’ diarrhea is something that affects a lot of people after they have been traveling for a few days or about a week. Not always, but it tends to mostly affect people traveling from countries in North America and Europe to places where the local food, water, bacteria, and hygiene systems are different from what their bodies are used to. It is not because those countries are dirty in a simple sense. It is usually because the traveler is suddenly exposed to microbes their body has not met before.
The main symptom of travelers’ diarrhea is, as the name suggests, diarrhea. It can also come with stomach cramps, fatigue, nausea, flu-like symptoms, and sometimes a fever. Some of these symptoms are the body’s way of trying to get rid of the bacteria, but the bacteria have evolved to exploit these mechanisms. This is what makes diarrhea such an interesting problem.
We all have bacteria that live in our intestines, and these are often known as “good” bacteria. We need them to live. We cannot digest all of the food that we eat, so these bacteria live in our intestines and help break some of it down. In return for a food source and a safe place to live, they give us useful compounds, help us absorb nutrients, and help protect our gut. It is a symbiotic relationship that has evolved over hundreds of thousands of years. These bacteria are safe because they live with us rather than against us. However, there are other bacteria that are not safe, and some of them produce toxins.
Travelers’ diarrhea is often caused by bacteria such as E. coli and Campylobacter. E. coli is one of the most common. When a person eats something contaminated with E. coli, the bacteria pass through the stomach and reach the intestines. This is not easy for them because stomach acid is designed to kill microbes. However, some types of E. coli are very good at surviving acid. They can detect the low pH of the stomach and switch on systems that help protect them and repair damage. Once they are in the intestine, they attach to the intestinal wall and go to work.
Diarrhea is one natural mechanism the body has to get rid of toxins and harmful microbes. The intestines produce more water, which helps flush out the system. This can be a good thing. However, in the case of travelers’ diarrhea, the bacteria are partly hijacking that system. Some E. coli produce toxins that interfere with ion movement in the gut. These toxins affect the movement of salts such as sodium and chloride. Water follows salt, so when more salt moves into the intestine, more water is pulled into the intestine as well. The intestines fill with water, and watery diarrhea is produced.
This is why diarrhea can be dangerous. Diarrhea itself is not usually the thing that kills people. The danger is dehydration and the loss of salts that the body needs in order to keep working. In wealthy countries, this can usually be treated fairly easily with clean water, oral rehydration solution, and medical help when necessary. In poorer areas, where clean water and medical care may be harder to access, diarrheal diseases can still be deadly, especially for young children.
So, what is in it for the bacteria? What reason does it have to make a system that flushes it out? E. coli bacteria are spread through fecal matter. And the goal of a bacterium, if a bacterium can be said to have a goal, is to reproduce and spread itself. The bacteria reproduce in an infected person’s intestine. Under perfect conditions, some E. coli can double roughly every 20 minutes. That means 10 bacteria could become 80 in an hour, 640 in two hours, and over 40,000 in four hours. Real conditions inside the body are not perfect because the immune system is fighting back, but the point is that bacteria can multiply extremely quickly.
These bacteria cannot stay in one host forever. If they remain trapped inside one person, they have nowhere else to go. Being expelled in watery diarrhea gives them a way out. In places with poor sanitation, the bacteria can then contaminate water, hands, surfaces, or food. Another person eats or drinks them, and the cycle begins again. From the body’s point of view, diarrhea is an attempt to flush out the invader. From the bacteria’s point of view, it is a way to escape and spread to a new host.
Travelers’ diarrhea is most common in places where sanitation, water treatment, or food preparation methods are different from what the traveler is used to. If sewage systems are poor, or food is washed in contaminated water, E. coli can get onto food. This is the main way travelers become infected. Washing hands with soap is very effective because it loosens microbes and helps wash them away. Cooking food thoroughly also kills many bacteria, which is why raw foods can be risky when traveling.
For many healthy adults, travelers’ diarrhea is unpleasant but short-lived. It often passes in a few days. The most important thing is to replace the water and salts that are lost. However, it should not be ignored if there is blood in the stool, a high fever, severe dehydration, or symptoms that do not improve. A person who spends a long time in one place may become less vulnerable to some local bacteria over time, but there are many different causes of diarrhea, so immunity is never complete. And this is what I learned today.
Sources
https://www.mayoclinic.org/diseases-conditions/travelers-diarrhea/symptoms-causes/syc-20352182
https://www.sciencedaily.com/releases/2015/01/150114072746.htm
https://en.wikipedia.org/wiki/Travelers%27_diarrhea
Photo by Ketut Subiyanto: https://www.pexels.com/photo/backpackers-on-railway-station-4901995/