Tropical disease

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Tropical diseases are diseases that are prevalent in or unique to tropical and subtropical regions. [1] 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. However, many were present in northern Europe and northern America in the 17th and 18th centuries before modern understanding of disease causation. The initial impetus for tropical medicine was to protect the health of colonial settlers, notably in India under the British Raj. [2] 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 most of the diseases listed here, and many do not have cures.


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 to non-tropical countries. [3] [4]

Health programmes

In 1975 the Special Programme for Research and Training in Tropical Diseases (TDR) was established to focus on neglected infectious diseases which disproportionately affect poor and marginalized populations in developing regions of Africa, Asia, Central America and North South America. It was established at the World Health Organization, which is the executing agency, and is co-sponsored by the United Nations Children's Fund, United Nations Development Programme, the World Bank and the World Health Organization.

TDR's vision is to foster an effective global research effort on infectious diseases of poverty in which disease endemic countries play a pivotal role. It has a dual mission of developing new tools and strategies against these diseases, and to develop the research and leadership capacity in the countries where the diseases occur. The TDR secretariat is based in Geneva, Switzerland, but the work is conducted throughout the world through many partners and funded grants.

Some examples of work include helping to develop new treatments for diseases, such as ivermectin for onchocerciasis (river blindness); showing how packaging can improve use of artemesinin-combination treatment (ACT) for malaria; demonstrating the effectiveness of bednets to prevent mosquito bites and malaria; and documenting how community-based and community-led programmes increases distribution of multiple treatments. TDR history

The current TDR disease portfolio includes the following entries: [5]

Historical TDR disease portfolio
DiseaseWhen added Pathogen Primary vector Primary endemic areasFrequencyAnnual deaths Symptoms Complications
Malaria 1975 Plasmodium falciparum and four other Plasmodium species of protazoa Anopheles mosquitoes throughout the tropics228 million (2018)405,000 (2018) fever, tiredness, vomiting, headache yellow skin, seizures, coma, death
Schistosomiasis /ˌʃɪstəsəˈməsɪs/ [6] [7] (snail fever, bilharzia, "schisto")1975 Schistosoma flatworms (blood flukes) freshwater snails throughout the tropics252 million (2015)4,400–200,000 abdominal pain, diarrhea, bloody stool, blood in the urine. In children, it may cause poor growth and learning difficulty. Liver damage, kidney failure, infertility, bladder cancer
Lymphatic filariasis 1975 Wuchereria bancrofti, Brugia malayi, and Brugia timori filarial worms mosquitoes throughout the tropics38.5 million (2015)few lymphoedema, elephantiasis, hydrocele
Onchocerciasis /ˌɒŋksɜːrˈkəsɪs,-ˈs-/ [8] [9] (river blindness)1975 Onchocerca volvulus filarial worms [10] Simuliidae black fliessub-Saharan Africa15.5 million (2015)0 itching, papules edema, lymphadenopathy, visual impairment, blindness
Chagas disease (American trypanosomiasis)1975 Trypanosoma cruzi protozoa Triatominae kissing bugsSouth America6.2 million (2017)7,900 (2017) fever, swollen lymph nodes, headache heart failure, enlarged esophagus, enlarged colon
African trypanosomiasis (sleeping sickness)1975 Trypanosoma brucei gambiense and T. b. rhodesiense protozoa Glossina tsetse fliessub-Saharan Africa11,000 (2015)3,500 (2015)first stage: fever, headache, itchiness, joint pain

second stage: insomnia, confusion, ataxia, hemiparesis, paralysis

anemia, endocrine disfunction, cardiac disfunction, kidney dysfunction, coma, death
Leishmaniasis 1975 Leishmania protozoa Phlebotominae sandfliesthroughout the tropics4–12 million24,200 (2015) skin ulcers fever, anemia, enlarged liver, enlarged spleen, death
Leprosy (Hansen's disease)1975 Mycobacterium leprae and M. lepromatosis mycobacteriaextensive contact (probably airborne disease)throughout the tropics209,000 (2018)few skin lesions, [11] numbness permanent damage to the skin, nerves, limbs, and eyes
Dengue fever 1999 dengue virus Aedes aegypti and other Aedes mosquitoes tropical Asia390 million (2020)40,000 fever, headache, muscle and joint pain, rash, vomiting, diarrhea low levels of blood platelets, hypotension, hemorrhage, shock
Tuberculosis (TB, consumption)1999 Mycobacterium tuberculosis mycobacteria airborne disease worldwide10 million (active, 2018),

2 billion (latent, 2018)

1.5 million (2018) chronic cough, fever, cough with bloody mucus, weight loss death
TB-HIV coinfection 1999 HIV + Mycobacterium tuberculosis sexual contact + airborne disease Africa1.2 million (2015)251,000 (2018)
Sexually transmitted infections (notably syphilis, gonorrhoea, chlamydia, trichomoniasis, hepatitis B, HSV, HIV, and HPV)2000bacteria, parasite, viruses sexual contact worldwidevariousvarious
Although leprosy and tuberculosis are not exclusively tropical diseases, their high incidence in the tropics justifies their inclusion.
People living with HIV are 19 (15-22) times more likely to develop active TB disease than people without HIV.

Other neglected tropical diseases

Additional neglected tropical diseases include: [12]

DiseaseCausative AgentComments
Hookworm Ancylostoma duodenale and Necator americanus
Trichuriasis Trichuris trichiura
Treponematoses Treponema pallidum pertenue, Treponema pallidum endemicum, Treponema pallidum carateum, Treponema pallidum pallidum
Buruli ulcer Mycobacterium ulcerans
Dracunculiasis Dracunculus medinensis
Leptospirosis Leptospira
Strongyloidiasis Strongyloides stercoralis
Foodborne trematodiases Trematoda
Neurocysticercosis Taenia solium
Scabies Sarcoptes scabiei
Flavivirus Infections Yellow fever virus, West Nile virus, dengue virus, Tick-borne encephalitis virus, Zika 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.

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.[ citation needed ]

Climate change, global warming caused by the greenhouse effect, and the resulting increase in global temperatures, are possibly 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. [13] [14] 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. [15] 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.

Prevention and treatment

Disability-adjusted life year for tropical diseases per 100,000 inhabitants. These include trypanosomiasis, chagas disease, schistosomiasis, leishmaniasis, lymphatic filariasis, onchocerciasis.
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Disability-adjusted life year for tropical diseases per 100,000 inhabitants. These include trypanosomiasis, chagas disease, schistosomiasis, leishmaniasis, lymphatic filariasis, onchocerciasis.
  no data

Vector-borne diseases

Vectors are living organisms that pass disease between humans or from animal to human. The vector carrying the highest number of diseases is the mosquito, which is responsible for the tropical diseases dengue and malaria. [16] Many different approaches have been taken to treat and prevent these diseases. NIH-funded research has produced genetically modify mosquitoes that are unable to spread diseases such as malaria. [17] An issue with this approach is global accessibility to genetic engineering technology; Approximately 50% of scientists in the field do not have access to information on genetically modified mosquito trials being conducted. [18]

Other prevention methods include:

Sexually transmitted diseases

Both pharmacologic pre-exposure prophylaxis (to prevent disease before exposure to the environment and/or vector) and pharmacologic post-exposure prophylaxis (to prevent disease after exposure to the environment and/or vector) are used to prevent and treat HIV [ citation needed ]

Community approaches

Assisting with economic development in endemic regions can contribute to prevention and treatment of tropical diseases. For example, microloans enable communities to invest in health programs that lead to more effective disease treatment and prevention technology. [19]

Educational campaigns can aid in the prevention of various diseases. Educating children about how diseases spread and how they can be prevented has proven to be effective in practicing preventative measures. [20] Educational campaigns can yield significant benefits at low costs.

Other approaches

See also

Related Research Articles

Malaria Mosquito-borne infectious disease

Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. Symptoms usually begin ten to fifteen days after being bitten by an infected mosquito. If not properly treated, people may have recurrences of the disease months later. In those who have recently survived an infection, reinfection usually causes milder symptoms. This partial resistance disappears over months to years if the person has no continuing exposure to malaria.

Filariasis Parasitic disease caused by a family of nematode worms

Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea type. These are spread by blood-feeding insects such as black flies and mosquitoes. They belong to the group of diseases called helminthiases.

London School of Hygiene & Tropical Medicine Public research university

The London School of Hygiene & Tropical Medicine (LSHTM) is a public research university in Bloomsbury, Camden, and a constituent college of the University of London that specialises in public health and tropical medicine. On successful completion of their studies, its students gain a University of London degree.

<i>Anopheles</i> Genus of mosquito

Anopheles is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus Plasmodium, which cause malaria in humans in endemic areas. Anopheles gambiae is one of the best known, because of its predominant role in the transmission of the most dangerous malaria parasite species – Plasmodium falciparum.

Liverpool School of Tropical Medicine Tropical medicine teaching and research institution

The Liverpool School of Tropical Medicine (LSTM) is a higher education institution with degree awarding powers and registered charity located in Liverpool, United Kingdom. Established in 1898, it was the first institution in the world dedicated to research and teaching in tropical medicine. The school has a research portfolio of over £220 million, assisted by funding from organisations such as the Bill & Melinda Gates Foundation, Wellcome Trust and Department for International Development (DFID).

Travel medicine branch of medicine that deals with the prevention and management of health problems of international travelers

Travel medicine or emporiatrics is the branch of medicine that deals with the prevention and management of health problems of international travelers.

Tropical medicine medical specialty

Tropical medicine is an interdisciplinary branch of medicine that deals with health issues that occur uniquely, are more widespread, or are more difficult to control in tropical and subtropical regions.

<i>Brugia malayi</i> species of parasitic worm

Brugia malayi is a nematode (roundworm), one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower limbs. The two other filarial causes of lymphatic filariasis are Wuchereria bancrofti and Brugia timori, which both differ from B. malayi morphologically, symptomatically, and in geographical extent.

<i>Plasmodium vivax</i> species of malaria parasite

Plasmodium vivax is a protozoal parasite and a human pathogen. This parasite is the most frequent and widely distributed cause of recurring malaria. Although it is less virulent than Plasmodium falciparum, the deadliest of the five human malaria parasites, P. vivax malaria infections can lead to severe disease and death, often due to splenomegaly. P. vivax is carried by the female Anopheles mosquito; the males do not bite.

Lymphatic filariasis human disease caused by parasitic worms

Lymphatic filariasis is a human disease caused by parasitic worms known as filarial worms. Most cases of the disease have no symptoms. Some people, however, develop a syndrome called elephantiasis, which is marked by severe swelling in the arms, legs, breasts, or genitals. The skin may become thicker as well, and the condition may become painful. The changes to the body have the potential to harm the person's social and economic situation.

Neglected tropical diseases Diverse group of tropical infection diseases which are common in developing countries

Neglected tropical diseases (NTDs) are a diverse group of tropical infections which are common in low-income populations in developing regions of Africa, Asia, and the Americas. They are caused by a variety of pathogens such as viruses, bacteria, protozoa and parasitic worms (helminths). These diseases are contrasted with the big three infectious diseases, which generally receive greater treatment and research funding. In sub-Saharan Africa, the effect of these diseases as a group is comparable to malaria and tuberculosis. NTD co-infection can also make HIV/AIDS and tuberculosis more deadly.

Medical entomology study of insect impacts on human health

The discipline of medical entomology, or public health entomology, and also veterinary entomology is focused upon insects and arthropods that impact human health. Veterinary entomology is included in this category, because many animal diseases can "jump species" and become a human health threat, for example, bovine encephalitis. Medical entomology also includes scientific research on the behavior, ecology, and epidemiology of arthropod disease vectors, and involves a tremendous outreach to the public, including local and state officials and other stake holders in the interest of public safety.

Vector (epidemiology) Agent that carries and transmits an infectious pathogen into another living organism

In epidemiology, a disease vector is any agent which carries and transmits an infectious pathogen into another living organism; agents regarded as vectors are organisms, such as intermediate parasites or microbes.

Peter Hotez American academic

Peter Jay Hotez is an American scientist, pediatrician, and advocate in the fields of global health, vaccinology, and neglected tropical disease control. He serves as founding dean of the National School of Tropical Medicine and Professor of Pediatrics and Molecular Virology & Microbiology at Baylor College of Medicine, where he is also Director of the Texas Children's Hospital Center for Vaccine Development and Texas Children’s Hospital Endowed Chair in Tropical Pediatrics. Hotez served previously as President of the American Society of Tropical Medicine and Hygiene and is a founding Editor-in-Chief of PLOS Neglected Tropical Diseases. He is also the co-director of Parasites Without Borders, a global nonprofit organization with a focus on those suffering from parasitic diseases in subtropical environments.

Mosquito-borne disease diseases caused by bacteria, viruses or parasites transmitted by mosquitoes

Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people get a mosquito-borne illness each year resulting in over one million deaths.

The American Society of Tropical Medicine and Hygiene (ASTMH) is a non-profit organization of scientists, clinicians, students and program professionals whose longstanding mission is to promote global health through the prevention and control of infectious and other diseases that disproportionately afflict the global poor. ASTMH members work in areas of research, health care and education that encompass laboratory science, international field studies, clinical care and country-wide programs of disease control. The current organization was formed in 1951 with the amalgamation of the American Society of Tropical Medicine, founded in 1903, and the National Malaria Society, founded in 1941.

Neglected tropical diseases (NTDs) are a set of infectious diseases affecting an estimated 1.4 billion people worldwide. The classification of this group of neglected diseases is linked to their frequent neglect in public and private sector expenditure and attention at local, national, and international levels, and their concentration among the poor. Research and development yielding safe, effective drugs and vaccines for their treatment and prevention has been recognized as a global health priority.

Janet Hemingway British parasitologist

Janet Hemingway is a British entomologist, Professor of Insect Molecular Biology and Director of the Liverpool School of Tropical Medicine (LSTM). She also works on advocacy and resource mobilisation at the Innovative Vector Control Consortium (IVCC), and is International Director of the Joint Centre for Infectious Diseases Research, Jizan, Saudi Arabia. She is "the youngest woman to ever to become a full professor in the UK".

Uche Veronica Amazigo is a professor of Medical Parasitology and public health specialist. She is a fellow of the Nigerian Academy of Science who was elected into the Academy's Fellowship at its Annual General Meeting held in January, 2015. In 2012, she won the Prince Mahidol Award for outstanding contributions to public health. She is best known for her research on onchocerciasis and her consequent contributions to the World Health Organization (WHO).

Airport malaria occurs when a malaria infected female Anopheles mosquito travels by aircraft from a country where malaria is common

Airport malaria, sometimes known as baggage, luggage or suitcasemalaria, occurs when a malaria infected female Anopheles mosquito travels by aircraft from a country where malaria is common, arrives in a country where malaria is usually not found, and bites a person at or around the vicinity of the airport, or if the climate is suitable, travels in luggage and bites a person further away. The infected person usually presents with a fever in the absence of a recent travel history. There is often no suspicion of malaria, resulting in a delay in diagnosis and often death. Other causes of imported malaria need to be excluded first.


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Further reading