“Traveler’s diseases” is a broad term for bacterial, viral, fungal, and parasitic infections that may be acquired when someone travels away from home, especially when traveling from a developed or industrialized area to a less developed area. (Some of the conditions discussed in this article, however, can be acquired while at home, not just while traveling, such as HIV and hepatitis). Every travel destination and every geographical location has its hazards, including home. Those who live in a place, however, are generally aware of their own diseases and dangers and do their best to make accommodations for them. In Montana, for instance, you don’t feed the bears, you avoid poison ivy, stay aware in rattlesnake habitat, wear long-sleeved clothes during tick season (to avoid Rocky Mountain Spotted Fever), don’t drink the water from mountain streams (to avoid the parasite Giardia lamblia), avoid black widow spiders, treat all rodent droppings with care (to avoid hantavirus), and wear insecticide to avoid bites from mosquitoes carrying West Nile virus.

While bears and spiders and snakes are outside the scope of an article on microorganisms, it illustrates the need for visitors to a region to evaluate the risks that they may encounter. Staying in an urban hotel in a developed country for a few days can be very different from a two-week outdoor adventure in tropical South America. Travelers should educate themselves and discuss with their doctors their destinations, expected lengths of stay, and planned activities. With the proper care, many traveler’s diseases are preventable – through avoidance of the carrier’s (vector’s) environment, avoidance of risky behaviors, vigilant care with food and water, chemoprophylaxis (medicines taken before and during travel to prevent a specific illness), and vaccines.

Traveler’s diseases can be acquired through contaminated food or water, from animal droppings, and from soil. Close exposure to infected animals and physical contact with animal hides can also put someone at risk. People will usually not be able to see, smell, or taste the contamination. Diseases are also carried by vectors such as biting mosquitoes, flies, and ticks. Some can be acquired from swimming in freshwater and by walking on the beach with bare feet, while others are passed from person to person – through close contact, needle sharing, blood, and unprotected sex. The symptoms of some diseases may be so mild and self-limited that they go unnoticed; many may be a miserable annoyance for a few days, and a few may cause an acute medical emergency. There are diseases that may not emerge until the traveler has returned home, with symptoms that may resolve, cycle, grow progressively worse, or linger. Left untreated, a few of the diseases can lead to blindness, organ failure, coma, and death.

The most frequently encountered traveler’s illnesses are diarrhea, nausea, vomiting, fever, and skin manifestations (rashes, sores, swelling, etc). Also seen are hepatitis (liver inflammation) and its accompanying jaundice, headaches, meningitis and/or encephalitis. Some diseases will also cause respiratory symptoms – coughing and/or difficulty breathing.

Some diseases are global in nature - they are found throughout the world and, unless prevented through vaccination, frequently cause childhood illnesses. In some cases, these illnesses can lead to lifelong complications. Many nations have vaccination programs to decrease the number of people who contract conditions such as measles, rubella (German measles), mumps, and polio. In areas that are unable to uniformly vaccinate their populations, these conditions can be endemic and/or there may be epidemics (outbreaks) of the disease. Travelers who are not protected through previous vaccinations, young children who have not been fully immunized, and patients who are immunocompromised may be at an increased risk of contracting one of these infections. Adopted children and immigrants to the United States may bring these and other traveler’s diseases with them to the U.S. and should be evaluated for them.

Traveler’s diarrhea can be caused by a variety of bacteria, viruses, and parasites throughout the world. These microorganisms are found in water and food wherever sanitation and food handling practices are poor or inconsistent. People are often acclimatized to their own local bacteria and viruses but affected by microorganisms in other places. Parasites can affect both local inhabitants and those who travel.

Some viral and bacterial diarrheas tend to occur within a few hours of infection and may be self-limiting. Some, such as Salmonella and Shigella, have a 48-72 hour incubation period. Parasitic diarrheas tend to have a longer incubation time and, without treatment, may become chronic illnesses in some individuals.

Hepatitis A virus (HAV), which can cause liver inflammation and jaundice, can also be acquired from contaminated food and water. Infection with hepatitis B virus (HBV) and/or hepatitis C virus (HCV) may cause symptoms similar to hepatitis A, but they are transmitted through exposure to blood and body fluids, sexual contact, or perinatally (mother to infant). Risky behaviors, such as unprotected sex or acquiring a tattoo, may also expose travelers to HIV and to other sexually transmitted diseases.

The most common infections associated with fever are malaria, dengue fever, and yellow fever. All of these conditions are carried by mosquitoes, and they are endemic in tropical areas of the world. A vaccine is available for yellow fever, and proof of vaccination may be required for entry into some countries. Chemoprophylaxis is available for malaria. Dengue fever is a rapidly expanding disease (found in more and more geographical areas) that is causing progressively larger epidemics. There is no preventative treatment for dengue; it can be avoided by taking measures to avoid mosquito bites.

Travelers can also catch colds and the flu while in airplanes and other modes of transport while in route to or from their travel destination.

For summary information on common traveler's diseases, where they are found, causes of diarrhea, and vaccine availability, click to download the PDF table. Otherwise, go on to the next two pages for information on testing and treatment.