What are they?
“Travellers' diseases” is a broad term for bacterial, viral, fungal, and parasitic infections that may be caught when someone travels away from home, especially when travelling 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 travelling, such as HIV and hepatitis). Every travel destination and every area has its hazards, including when travelling in the UK. 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. The British for instance, would be able to identify stinging nettles with ease but not venomous spiders!
While spiders and nettles are outside the scope of an article on microorganisms, it shows the need for travellers to understand the risks that they may come across. Staying in an city hotel in a developed country for a few days can be very different from a two-week outdoor adventure in Thailand or Malaysia . Travellers should educate themselves and discuss their destinations, expected lengths of stay, and planned activities with their GP or practice nurse. With the proper care, many travellers’ diseases are preventable, by avoiding particular environments, risky activities, careful choice food and source of water, and the appropriate use of medicines and vaccines.
Traveller’s diseases can be acquired through contaminated food or water, from animal droppings, and from soil. Close exposure to infected animals and contact with animal skin can put someone at risk. People will usually not be able to see, smell, or taste the contamination. Diseases are also carried by biting mosquitoes, flies, and ticks. Some can be picked up 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 become apparent until the traveller has returned home with symptoms that may resolve, cycle, grow gradually worse, or stay for a long time. Left untreated, a few of the diseases can lead to blindness, organ failure, coma, and death.
The most frequently seen traveller’s illnesses are diarrhoea, nausea, being sick, fever, and skin manifestations (rashes, sores, swelling, etc). Also seen are hepatitis (liver inflammation) and accompanying jaundice, headaches, meningitis and/or encephalitis. Some diseases will also cause breathing problems and coughing.
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 get conditions such as measles, rubella (German measles), mumps, and polio. In areas that are unable to vaccinate all of their population, these conditions may be very common. Travellers 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 getting one of these infections. Travellers from foreign countries may also have diseases not normally seen in the UK.
Travellers' diarrhoea can be caused by a variety of bacteria, viruses, and parasites throughout the world. These microorganisms may be found in water and food wherever sanitation and food handling practices are poor. People are often get used to their own local bacteria and viruses but are affected by those present in other places. Parasites can affect both local inhabitants and those who travel.
Some viral and bacterial diarrhoeas tend to occur within a few hours of infection and may be self-limiting and get better. Some, such as Salmonella and Shigella, have a 48-72 hour incubation period. Parasitic diarrhoeas tend to have a longer incubation time and, without treatment, may become chronic illnesses in some individuals.
Hepatitis A virus, which can cause liver inflammation and jaundice, can also be picked up 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 picked up through exposure to blood and body fluids, sexual contact, or perinatally (mother to infant). Risky behaviours, such as unprotected sex, may also expose travellers to HIV and other sexually transmitted diseases.
The most common infections which produce fever are malaria, dengue fever, and yellow fever. All of these diseases are carried by mosquitoes, and they are very common 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. Regular medication is available to prevent malaria. Dengue fever is a rapidly growing disease, found in an increasing number of countries, and is causing progressively larger epidemics. There is no preventative treatment for dengue but can be avoided by taking measures to avoid mosquito bites.
Travellers can also catch colds and the flu while in airplanes and other modes of transport while travelling to or from their travel destination.
It is important to identify the cause of the disease in travellers, not only to treat the individual but also to prevent and document the spread of the disease, both in returning travellers and in the countries they visited.
Causes of bacterial diarrhoea may be identified with a stool culture and may be treated with antimicrobial agents when symptoms appear and/or may get better without the need for further tests to identify the pathogen. Parasitic causes of diarrhoea can be identified through the OCP (ova and parasite) stool test. This test is used to identify parasites and their eggs in a fresh or specially preserved stool sample. For some parasites, such as Giardia intestinalis (lamblia), antigen tests have been developed. These tests identify proteins associated with the parasite and can be useful when parasites are present in low numbers. Because identifying the cause of viral diarrhoea is complex, viral causes of diarrhoea may not be identified by specific cultures or tests unless the virus causes a large number of people to become ill, such as an outbreak of norovirus on a cruise ship.
The parasite that causes malaria (Plasmodium spp.) infects red blood cells. It can be identified by collecting a blood sample and examining specially stained “thick and thin” blood smears on slides under the microscope. Many of the other travellers’ diseases can be identified either by growing the microorganism, looking at it under the microscope, and/or testing for antibodies or antigens. Patients who return from travelling with a a short or longer lasting disease should see their doctor, who may occasionally suggest a consultation with an infectious disease and/or tropical medicine specialist.
Sometimes x-rays or CT scans may be used to look at body organs, such as the lungs or liver, for evidence of infection or damage.