What are Tropical Diseases?

Tropical diseases are diseases that are prevalent in or unique to tropical and subtropical regions. The diseases are less prevalent in temperate climates, due in part to the occurrence of a cold season, which controls the insect population by forcing hibernation. Insects such as mosquitoes and flies are by far the most common disease carrier, or vector. These insects may carry a parasite, bacterium or virus that is infectious to humans and animals. Most often disease is transmitted by an insect "bite", which causes transmission of the infectious agent through subcutaneous blood exchange. Vaccines are not available for any of the diseases listed here.

Human exploration of tropical rainforests, deforestation, rising immigration and increased international air travel and other tourism to tropical regions has led to an increased incidence of such diseases.

Tropical Disease Special Programme for Research and Training in Tropical Diseases (TDR)

In 1975 the United Nations Children's Fund, the United Nations Development Programme, the World Bank and the World Health Organization established the Special Programme for Research and Training in Tropical Diseases (TDR) to focus on neglected infectious diseases which disproportionately affect poor and marginalized populations in developing regions of Africa, Asia, Central America and South America. The current TDR disease portfolio includes the following entries:

Chagas disease (also called American trypanosomiasis) is a parasitic disease which occurs in the Americas, particularly in South America. Its pathogenic agent is a flagellate protozoan named Trypanosoma cruzi.

African trypanosomiasis or sleeping sickness, is a parasitic disease, caused by protozoa called trypansomes. The two responsible for African trypanosomiasis are Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense.These parasites are transmitted by the tsetse fly

Leishmaniasis caused by protozoan parasites of the genus Leishmania, and transmitted by the bite of certain species of sand fly.

Leprosy (or Hansen's disease) is a chronic infectious disease caused by Mycobacterium leprae. Leprosy is primarily a granulomatous disease of the peripheral nerves and mucosa of the upper respiratory tract; skin lesions are the primary external symptom. Left untreated, leprosy can be progressive, causing permanent damage to the skin, nerves, limbs, and eyes. Contrary to popular conception, leprosy does not cause body parts to simply fall off, and it differs from tzaraath, the malady described in the Hebrew scriptures and previously translated into English as leprosy.

Lymphatic filariasis is a parasitic disease caused by thread-like parasitic filarial worms called nematode worms, all transmitted by mosquitoes. Loa loa is another filarial parasite transmitted by the deer fly. 120 million people are infected worldwide. It is carried by over half the population in the most severe endemic areas. The most noticeable symptom is elephantiasis: a thickening of the skin and underlying tissues.

Malaria caused by a Protozoan parasites transmitted by female Anopheles mosquitoes, as they are the blood-feeders. The disease is caused by species of the genus Plasmodium. Malaria infects 300-500 million people each year, killing more than 1 million.

Onchocerciasis or river blindness is the world's second leading infectious cause of blindness. It is caused by Onchocerca volvulus, a parasitic worm. It is transmitted through the bite of a black fly. The worms spread throughout the body, and when they die, they cause intense itching and a strong immune system response that can destroy nearby tissue, such as the eye. About 18 million people are currently infected with this parasite. Approximately 300,000 have been irreversibly blinded by it.

Schistosomiasis also known as schisto or snail fever, is a parasitic disease caused by several species of flatworm in areas with freshwater snails, which may carry the parasite. The most common form of transmission is by wading or swimming in lakes, ponds and other bodies of water containing the snails and the parasite. More than 200 million people worldwide are infected by schistosomiasis.

Sexually transmitted infections

TB/HIV coinfection

Tuberculosis (abbreviated as TB), is a bacterial infection of the lungs or other tissues, which is highly prevalent in the world, with mortality over 50% if untreated. It is a communicable disease, transmitted by aerosol expectorant from a cough, sneeze, speak, kiss, or spit. Over one-third of the world's population has been infected by the TB bacterium.

Tropical Disease Other neglected tropical diseases

Additional neglected tropical diseases include:

DiseaseCausative Agent
HookwormAncylostoma duodenale and Necator americanus
TrichuriasisTrichuris trichiura
TreponematosesTreponema pallidum pertenue, Treponema pallidum endemicum, Treponema pallidum carateum, Treponema pallidum pallidum
Buruli ulcerMycobacterium ulcerans
Human African trypanosomiasisTrypanosoma brucei, Trypanosoma gambiense
DracunculiasisDracunculus medinensis
StrongyloidiasisStrongyloides stercoralis
Foodborne trematodiasesTrematoda
NeurocysticercosisTaenia solium
ScabiesSarcoptes scabiei
Flavivirus InfectionsYellow fever virus, West Nile virus, dengue virus, Tick-borne encephalitis virus

Some tropical diseases are very rare, but may occur in sudden epidemics, such as the Ebola hemorrhagic fever, Lassa fever and the Marburg virus. There are hundreds of different tropical diseases which are less known or rarer, but that, nonetheless, have importance for public health.

Tropical Disease Relation of climate to tropical diseases

The so-called "exotic" diseases in the tropics have long been noted both by travelers, explorers, etc., as well as by physicians. One obvious reason is that the hot climate present during all the year and the larger volume of rains directly affect the formation of breeding grounds, the larger number and variety of natural reservoirs and animal diseases that can be transmitted to humans (zoonosis), the largest number of possible insect vectors of diseases. It is possible also that higher temperatures may favor the replication of pathogenic agents both inside and outside biological organisms. Socio-economic factors may be also in operation, since most of the poorest nations of the world are in the tropics. Tropical countries like Brazil, which have improved their socio-economic situation and invested in hygiene, public health and the combat of transmissible diseases have achieved dramatic results in relation to the elimination or decrease of many endemic tropical diseases in their territory.

Climate change, global warming caused by the greenhouse effect, and the resulting increase in global temperatures, are causing tropical diseases and vectors to spread to higher altitudes in mountainous regions, and to higher latitudes that were previously spared, such as the Southern United States, the Mediterranean area, etc. For example, in the Monteverde cloud forest of Costa Rica, global warming enabled Chytridiomycosis, a tropical disease, to flourish and thus force into decline amphibian populations of the Monteverde Harlequin frog . Here, global warming raised the heights of orographic cloud formation, and thus produced cloud cover that would facilitate optimum growth conditions for the implicated pathogen, B. dendrobatidis.

Tropical Disease Prevention and treatment of tropical diseases

Some of the strategies for controlling tropical diseases include:

  • Draining wetlands to reduce populations of insects and other vectors.
  • The application of insecticides and/or insect repellents) to strategic surfaces such as: clothing, skin, buildings, insect habitats, and bed nets.
  • The use of a mosquito net over a bed (also known as a "bed net") to reduce nighttime transmission, since certain species of tropical mosquitoes feed mainly at night.
  • Use of water wells, and/or water filtration, water filters, or water treatment with water tablets to produce drinking water free of parasites.
  • Development and use of vaccines to promote disease immunity.
  • Pharmacologic pre-exposure prophylaxis (to prevent disease before exposure to the environment and/or vector).
  • Pharmacologic post-exposure prophylaxis (to prevent disease after exposure to the environment and/or vector).
  • Pharmacologic treatment (to treat disease after infection or infestation).
  • Assisting with economic development in endemic regions. For example by providing microloans to enable investments in more efficient and productive agriculture. This in turn can help subsistence farming to become more profitable, and these profits can be used by local populations for disease prevention and treatment, with the added benefit of reducing the poverty rate.

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