Tropical diseases areinfectious diseases that are prevalent in or unique totropical andsubtropical regions.[1] The diseases are less prevalent intemperate climates, due in part to the occurrence of a cold season, which controls the insect population by forcinghibernation. However, many were present inNorthern Europe andNorthern America in the 17th and 18th centuries before modern understanding of disease causation. The initial impetus fortropical medicine was to protect the health of colonial settlers, notably in India under theBritish Raj.[2] Insects such as mosquitoes and flies are by far the most common disease carrier, orvector. These insects may carry aparasite,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 throughsubcutaneous blood exchange. Vaccines are not available for most of the diseases listed here, and manydo 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] Of particular concern is thehabitat loss ofreservoir host species.[5]
In 1975 the Special Programme for Research and Training in Tropical Diseases (TDR) was established to focus onneglected 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 theWorld Health Organization, which is the executing agency, and is co-sponsored by theUnited Nations Children's Fund,United Nations Development Programme, theWorld Bank and theWorld Health Organization.[citation needed]
TDR's vision is to foster an effective global research effort on infectiousdiseases 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.[citation needed]
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:[6]
| Disease | When added | Pathogen | Primaryvector | Primaryendemic areas | Frequency | Annual deaths | Symptoms | Complications |
|---|---|---|---|---|---|---|---|---|
| Malaria | 1975 | Plasmodium falciparum and four otherPlasmodium species ofprotozoa | Anopheles mosquitoes | throughout the tropics | 241 million (2024)[7] | 627,000 (2024)[8] | fever,tiredness, vomiting, headache | yellow skin,seizures, coma, death |
| Schistosomiasis/ˌʃɪstəsəˈmaɪəsɪs/[9][10] (snail fever, bilharzia, "schisto") | 1975 | Schistosomaflatworms (blood flukes) | freshwater snails | throughout the tropics | 252 million (2021) | 11,792 (2021)[11] | abdominal pain, diarrhea,bloody stool,blood in the urine. In children, it may causepoor growth andlearning difficulty. | Liver damage, kidney failure,infertility,bladder cancer |
| Lymphatic filariasis | 1975 | Wuchereria bancrofti,Brugia malayi, andBrugia timorifilarial worms | mosquitoes | throughout the tropics | 38.5 million (2015) | few | lymphoedema,elephantiasis,hydrocele | |
| Onchocerciasis/ˌɒŋkoʊsɜːrˈkaɪəsɪs,-ˈsaɪ-/[12][13] (river blindness) | 1975 | Onchocerca volvulusfilarial worms[14] | Simuliidae black flies | sub-Saharan Africa | 15.5 million (2015) | 0 | itching,papules | edema,lymphadenopathy,visual impairment,blindness |
| Chagas disease (American trypanosomiasis) | 1975 | Trypanosoma cruziprotozoa | Triatominae kissing bugs | South America | 6.2 million (2017) | 7,900 (2017) | fever, swollenlymph nodes, headache | heart failure,enlarged esophagus,enlarged colon |
| African trypanosomiasis (sleeping sickness) | 1975 | Trypanosoma brucei gambiense andT. b. rhodesiense protozoa | Glossina tsetse flies | sub-Saharan Africa | 11,000 (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 sandflies | throughout the tropics | 4–12 million | 24,200 (2015) | skin ulcers | fever,anemia,enlarged liver,enlarged spleen, death |
| Leprosy† (Hansen's disease) | 1975 | Mycobacterium leprae andM. lepromatosis mycobacteria | extensive contact (probablyairborne disease) | throughout the tropics | 209,000 (2018) | few | skin lesions,[15]numbness | permanent damage to the skin, nerves, limbs, and eyes |
| Dengue fever | 1999 | dengue virus | Aedes aegypti and otherAedesmosquitoes | tropical Asia | 390 million (2020) | 40,000 | fever, headache,muscle andjoint pain,rash, vomiting,diarrhea | low levels of blood platelets,hypotension,hemorrhage,shock |
| Tuberculosis† (TB, consumption) | 1999 | Mycobacterium tuberculosis mycobacteria | airborne disease | worldwide | 10 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 | Africa | 1.2 million (2015) | 251,000 (2018) | ||
| Sexually transmitted infections (notablysyphilis,gonorrhoea,chlamydia,trichomoniasis,hepatitis B,HSV, HIV, andHPV) | 2000 | bacteria, parasite, viruses | sexual contact | worldwide | various | various |
Additionalneglected tropical diseases include:[16]
Some tropical diseases are very rare, but may occur in sudden epidemics, such as theEbola hemorrhagic fever,Lassa fever and theMarburg virus. There are hundreds of different tropical diseases which are less known or rarer, but that, nonetheless, have importance forpublic health.
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 ofnatural reservoirs and animal diseases that can be transmitted to humans (zoonosis), the largest number of possible insectvectors 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 inhygiene,public health and the combat of transmissible diseases have achieved dramatic results in relation to the elimination or decrease of manyendemic tropical diseases in their territory.[citation needed]
Climate change,global warming caused by thegreenhouse 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.[17][18] 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.[19] 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.[citation needed]
Human activities, particularly those driving climate change, are significantly influencing the spread and geographical range of tropical diseases. The burning of fossil fuels, deforestation, industrial agriculture, and urbanization release large amounts of greenhouse gases into the atmosphere, raising global temperatures and altering weather patterns. These environmental changes, such as increased rainfall, higher temperatures, and more frequent extreme weather events, create more favorable conditions for disease vectors like mosquitoes, which transmit diseases such as malaria, dengue, and Zika. In many cases, this has expanded the reach of tropical diseases into regions that were previously unaffected, including higher altitudes and temperate zones. Additionally, human-driven habitat destruction, such as the clearing of forests and wetlands, disrupts natural reservoirs and increases human-wildlife contact, further elevating the risk of zoonotic diseases crossing into human populations. As climate change continues, these activities will likely exacerbate the public health burden, especially in low-income regions that are most vulnerable to both the impacts of climate change and the diseases it helps spread.[20][21]
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.[22] 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.[23] 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.[24]
Other prevention methods include:
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.[25]
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.[26] Educational campaigns can yield significant benefits at low costs.[citation needed]
Recent advancements in vector control technologies are proving effective in reducing the transmission of mosquito-borne diseases like malaria, dengue, and Zika. Genetically modified (GM) mosquitoes, such asOxitec's mosquitoes, which prevent females from surviving to adulthood, have demonstrated over a 90% reduction in mosquito populations in field trials in Brazil.[27]
Another promising approach is the use ofWolbachia bacteria, which renders mosquitoes resistant to the dengue virus. A trial inYogyakarta, Indonesia, showed a 77% reduction in symptomatic dengue cases in areas with Wolbachia-infected mosquitoes.[28]
Additionally,integrated vector management (IVM), which combines biological controls, insecticides, and public education, has proven successful in reducing the transmission of arboviruses. These strategies offer more sustainable and eco-friendly solutions for controlling mosquito populations and preventing disease spread.[29]
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