There are a number of Tropical diseases that present a health risk to travellers that are not present in their own countries. This article is meant as a travellers introduction to the more common aspects of the subject.
Hot humid environments provide ideal conditions for a number of diseases, or their vectors, to survive and spread. Some of these are transmitted by insects, others are water borne or may be carried by foods, often in meat. A number are transmitted by human contact.
Simple precautions — vaccinations, condoms, mosquito nets and insect repellents, and taking care with food and drink — can greatly reduce the risks.
Many governments require visitors entering, or residents leaving, their countries to be vaccinated for a range of diseases. These requirements may often depend on what countries a traveller has visited or intends to visit. For example, if you have visited hot countries, most likely in Africa/Asia, then other countries may require evidence of Yellow fever vaccination before letting you in.
If you are bringing prescription medicine with you, carry a copy of the prescription.
Tropical sun is much stronger than at Northern latitudes. Sunglasses are almost essential. Many travellers need sunscreen. In places like China and India, many locals routinely carry parasols; consider emulating them. A hat can be a good idea, especially for balding men.
Consider Noel Coward's line "Only mad dogs and Englishmen go out in the noonday sun." You need to manage your time in the sun, avoiding the heat of the day. If partying until dawn is your style, do that, then sleep until 2. If not, consider rising around dawn to do your sightseeing before the crowds and the sun get too bad. Try a siesta, or a leisurely lunch in the shade, in the heat of the day.
Heatstroke can be a very serious illness. Drink plenty of bottled water. Consider carrying rehydration salts to replace what you lose by sweating. Soda water includes some salts.
Malaria - a parasitic infection transmitted by infective mosquitoes, malarial infections require immediate qualified diagnosis and treatment, preventatives and treatments are available - no vaccine is available
Dengue fever - a mosquito borne febrile virus transmitted by an infective Aedes aegypti or Aedes africanus mosquito. Causes high fever, headache, joint and muscle pain and may in some cases lead to a more severe manifestation, dengue hemorrhagic fever (DHF). Occurs in many tropical countries and is the most important tropical infectious disease after malaria and the worlds most serious (human) arbovirus disease. DHF infections require immediate qualified diagnosis and treatment - no vaccine is available
Chikungunya (CHIKV)- also known as epidemic polyarthritis and rash, and buggy creek virus. A febrile virus transmitted, like dengue by an infective Aedes aegypti or Aedes africanus mosquito. After 3-12 days flu-like symptoms develop including severe headaches, chills, fever, joint pain, nausea and vomiting - no vaccine is available
Cryptosporidiosis/Cryptosporidium/Crypto. Found worldwide, this disease is an untreated and chlorine treated water risk. It can even be spread if an infected person bathes in a treated public swimming pool. It causes diarrhea, cramps and fever. Last about 10 days but feces carry infection for weeks. Prevention by avoiding mouth coming into contact with infected water or fecal matter and maintaining scrupulous toilet and bathing hygiene after being infected to prevent reinfection of self or others. There is no cure. Prevented by boiling all drinking water, including tap water, in infected areas.
Diarrhea, typically caused by bacteria in food or drinks. Also known as Delhi Belly, Montezuma's Revenge, and so on, this is the most common ailment of all for travellers. Extreme forms include cholera (watery massive diarrhea) and dysentery (bloody diarrhea). A cholera vaccine is available, but rarely used due to its ineffectiveness and the unlikeliness of the average traveller contracting the disease.
Hepatitis A. Can be spread by food contaminated with feces (unwashed hands), where the virus remains active for days. Symptoms may not appear for a month after infection, and may continue for as long as six months. Hepatitis A is common almost everywhere except in countries with a high standard of hygiene (see map of areas with high infection rates: US CDC FAQ). A vaccine is available for hepatitis A, but this will not protect against the more virulent forms of hepatitis, such as B C.
Typhoid fever. Caused by the bacterium Salmonella enterica Typhi. It causes high fever, headache, malaise as well as other symptoms and is a general health problem in all less developed countries. Transmission is by contaminated food and water, especially in rural areas. A vaccination is available but offers no absolute safety, so the best options are precautions with what you drink & eat. See also http://www.cdc.gov/travel/diseases/typhoid.htm.
Schistosomiasis/Bilharzia is a nasty parasite that can be picked up by swimming in contaminated fresh water. The worm is carried by freshwater snails, and emerges daily into the water, where it is attracted to water turbulence, shadows, and chemicals found on human skin. While unlikely to be fatal, Schistosomiasis is a devastating disease, which should be treated as soon as possible. Symptoms include abdominal pain, diarrhea, coughing, genital sores, itching especially around the feet, but above all serious fatigue. Schistosomiasis, while present throughout much of the world, is primarily a problem in sub-Saharan Africa, and is easily, if unhappily, prevented by not swimming in fresh water.
Avian Influenza. A viral infection normally affecting birds but the Avian Influenza A virus has also been found, albeit extremely rarely, in some human infections. Current outbreaks among animals occurred in South-East Asia (Cambodia, China, Indonesia, Laos, Malaysia, Thailand, and Vietnam). The disease is transmitted to humans by contact with infected birds (especially poultry) and their excrements and may cause serious disease. Precautions include avoiding contact to wild birds and their excrements (as far as this is possible...). Avian influenza infection appears frequently in the news because it could be a source for new influenza strains to which no one has immunity and which have the potential to evolve to cause deadly epidemics. However, from the traveler's perspective the personal risk from avian influenza is extremely low. Travelers should obey recommendations on contact with poultry as a matter of civic duty, to prevent spreading the avian disease to birds in other countries. There is no vaccination available in the moment.
Ebola. Found largely in West Sub-Saharan Africa after contact with infected primates (human and non-human), this disease is fatal if not treated aggressively and early and has a 50-90% fatality rate. Get to a hospital immediately upon experiencing symptoms.
Hepatitis B and C. Can be spread by entry of blood or bodily fluids from an infected person into the body, such as through sexual contact, sharing of hypodermic needles, or blood transfusion or organ donation (theoretically, if screening were not performed). Unlike Hepatitis A, "Hepatitis B is not spread through food or water, sharing eating utensils, breastfeeding, hugging, kissing, coughing, sneezing or by casual contact" (US CDC FAQ) A vaccine is available to prevent Hepatitis B, but no vaccine is available to protect against Hepatitis C.
HIV (AIDS virus). HIV is transmitted in the same ways as hepatitis B. Abstinence or monogamy, safe sex, and an absolute ban on needle-sharing are wise precautions in any country of the world. Travellers should note that rare strains of HIV, such as HIV-2 or Group O HIV-1, occur predominantly in West Africa and may not be detected by some rapid HIV screening tests. Some strains of HIV prevalent in Africa and Asia may be more infectious by heterosexual intercourse (see avert.org for further information)
Influenza. The common Flu kills an estimated 36,000 Americans each year, and results in 200,000 hospitalizations per year. (CDC Flu Page) As a general precaution an annual vaccination is often recommended for the latest strains prevalent in the countries you are visiting.
Lassa fever. An acute viral illness that occurs in West Africa. In areas of Africa where the disease is endemic (that is, constantly present), Lassa fever is a significant cause of morbidity and mortality. While Lassa fever is mild or has no observable symptoms in about 80% of people infected with the virus, the remaining 20% have a severe multisystem disease. Lassa fever is also associated with occasional epidemics, during which the case-fatality rate can reach 50%.
Polio. Causes paralysis and nerve damage - easily preventable by an oral vaccination that should normally be given in early childhood. Although polio was nearly eradicated in recent years, it is currently experiencing a resurgence in several nations, so travelers should be sure that they have received proper vaccination and boosters.
SARS. Severe Acute Respiratory Syndrome - Caused by a common Corona virus that apparently crossed species and was highly infectious. Only a problem if undiagnosed travelers travel and spread the disease. Its control is an example of how unidentified (new) diseases are able to be controlled by simple but burdensome public health measures.
Tuberculosis. A third world disease due to poverty and poor health care. Can occur in first world countries where the health care system makes treatment expensive - generally responds to antibiotics but mis/incomplete treatment in some countries means antibiotic resistant strains are also a problem.
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