Tropical diseases are a globally known phenomenon, with a focus on poverty-stricken populations in developing countries—a situation largely ignored by pharmaceutical companies. Geographically, tropical diseases are omnipresent specifically in tropical and subtropical regions, while they may also be found in other parts of the world. According to the disease condition, tropical diseases can be transmitted through the soil, food, air, water, etc.

Mosquitoes are the most common vector that transmits these diseases from one person to another, and therefore, affected individuals live or work near a divesting waste area without proper sanitation. Drugs such as chloroquine are constantly losing their effectiveness against parasites, while drugs against some of the diseases do not exist yet. Consequently, these diseases have multiple influences and consequences, including death.

Tropical diseases lead to high death rates in a short period among those who are afflicted and affected because of social, economic, personal, and cultural factors. There is an awareness to prevent these diseases and protect oneself from getting them, but their insights are still poor. In this section, to give an overview of the topic, we try to explain what tropical diseases are and why they matter.

Biological agents (specifically viruses, bacteria, and parasites) that occur naturally more often in countries with weak economies and social structures and fewer resources directed toward healthcare are the ones most frequently responsible for causing tropical diseases. These include dengue fever, lymphatic filariasis, leishmaniasis, rabies, schistosomiasis, Buruli ulcer, Chagas disease, cysticercosis, typhus fever, arboviral encephalitis, leprosy, plague, elephantiasis, cutaneous leishmaniasis, onchocerciasis, meningoencephalitis, trypanosomiasis, echinococcosis, foodborne trematode infections, foodborne cestode infections, soil-transmitted nematode infections, trachoma, yaws, yellow fever, dracunculiasis, and many others.

Although tropical diseases are both a cause and a consequence of the impoverishment of the people affected, genotypic and phenotypic causes or susceptibility to tropical diseases are less well characterized only in part. It is thought, however, that most people with a shortage of immune function are affected. This includes neonates, pregnant women, and immunocompromised individuals. In countries with a tropical climate, almost all cases of infection with tropical diseases occur.

The role of tropical diseases in guiding public health policies has been recognized throughout history and has also led to the development of treatments. In general, the best present-day treatments are also available such that a good result occurs. Therefore, studies on this condition are fundamental to improving health outcomes in endemic areas as much as possible.

Common Tropical Diseases

Tropical diseases can be caused by bacteria, viruses, or parasites. Many of these diseases are transmitted and propagated by vectors or are transmitted by a faecal-oral route because of a lack of safe potable water supplies or poor personal hygiene and sanitation. The cost of secondary and tertiary healthcare for these diseases is enormous, and sometimes the poorest tend to be the most affected. Several common tropical diseases are discussed in brief below.

1. Malaria Causative Agent: The Plasmodium parasites are responsible for malaria. Transmission: Transmitted by a mosquito, mainly the infected female Anopheles mosquito. Symptoms: Most characteristic symptoms include headache, fever, and vomiting, with significant anaemia. Socio-Economic Impact: There are more than 200 different species of Anopheles mosquitoes, of which around 30–40 are vectors of malaria. Many species are anthropophilic, and such mosquitoes will bite humans at any time of day. Epidemiology: Malaria transmission occurs primarily in the tropical and subtropical regions on account of several interlinking factors. The disease is highly prevalent in African and Southeast Asian regions. In 2015, 214 million cases of malaria had been reported.

2. Dengue Fever Virus: It is caused by the Aedes aegypti mosquito. Transmission: Mainly transmitted by the bite of the female Aedes mosquito, primarily Aedes aegypti, followed by A. albopictus. Socio-Economic Impact: The victims of the disease, being institutionalized for a prolonged duration, add to the economic burden. Poor healthcare and suboptimal water management facilities are the contributing factors to the perpetuation of the disease.

3. Schistosomiasis Helminth: The diseases are caused by small, parasitic flatworms called schistosomes. The responsible species are Schistosoma haematobium, S. mansoni, S. japonicum, S. mekongi, and S. intercalatum. Transmission: Intermediate hosts are snails; the trematode larvae grow to mature adult parasites in the human host. In general, the infection persists or is delayed for several weeks. The eggs of the matured schistosomes are voided through urine or faeces.

4. Onchocerciasis (River Blindness) Helminth: The disease is caused by the worm-like parasite called Onchocerca volvulus. Transmission: The parasitic disease is transmitted by infective black fly species that breed well in fast-flowing water bodies. Socio-Economic Impact: Onchocerciasis is a primary head and neck infection and can cause inflammation, connective tissue disease, subcutaneous lumps, and terrible itching. It causes onchodermatitis, a chronic inflammatory state, which can be mild or disabling.

5. Chagas Protozoa: It is caused by the parasite Trypanosoma cruzi. Host: Mainly affects human hosts and occasionally domestic animals. Transmission: Spread via the congregation of humidity-loving insects. The infection can also occur through ingestion of food when it is contaminated by feces of an infected insect.

6. Leishmaniasis Protozoa: This is a vector-borne disease caused by over 25 species of the parasite Leishmania. Transmission: Usually, the protozoan parasites are transmitted to human hosts through the bite of an infected sandfly.

Treatment: The disease can be self-healing and mild, but antileishmanial drugs can be considered in severe cases. The first-line drugs are pentavalent antimony, sodium stibogluconate, and antibiotic pentamidine in severe visceral cases. The above diseases are prevalent in tropical countries.

Although preventive strategies have been developed in terms of vaccines, the disease burden remains a major issue. The education, awareness, and involvement of local communities in controlling the vector can be fruitful in controlling diseases. The cost of healthcare and the need for long-term institutionalization also require the intervention and support of public healthcare from governments.

Prevention and Control Strategies

Disease prevention and control have been central strategies in the management of tropical diseases. Prominent among these is the interruption of parasite or pathogen transmission in any of its various phases - from vector to human, from human to vector, or through the environment in the case of diseases due to soil and water contamination. Strategies to prevent or interfere with transmission are applicable across any scale.

At the community level, there is often a focus on reducing exposure to vectors or pathogens, particularly as many rapidly assume that human behaviour is the cause of morbidity. At the national or international level, the focus very often shifts towards reducing transmission - a shift towards environmental management in preventing and controlling transmission at intermediate levels outside of the personal household usually occurs.

Vector control is the most emblematic form of preventing and controlling transmission. Great advances have been made in vector control over the last few decades. Insecticide-treated bed nets have been very effective in reducing the transmission of malaria, with their effectiveness boosted massively by formulations that include long-lasting insecticides or drugs to kill and provide a mosquito expulsion effect as well. Indoor residual spraying is a direct working example of environmental management.

A great many other vector control techniques exist, from bio-larvicides along rivers to sterilized male mosquitoes and screening of houses, and many entomologists keep coming up with new ideas. Vaccination can break transmission as well as confer immunity. The primary prevention of many diseases at the human community level has often been the core of public health efforts - control or eradication of typhoid, better sewage and water in urban environments, greater public hygiene, and better living and working conditions.

However, some diseases are now known to persist despite being untreatable because of the existence of an animal reservoir. In such cases, the control focus in modern public health practice is often on the humans at risk from those diseased animals, and the environment they share. This is exemplified by wildlife and zoonotic diseases such as leptospirosis, henipaviruses, anthrax, monkeypox, and Ebola, as well as highly prevalent diseases such as Rickettsia.

Challenges in prevention and control include human resistance and resilience - but also intractable political and economic barriers, particularly concerning the unwillingness to invest in disease prevention. However, when funding is available for prevention and control approaches, effectiveness should be a consideration. Promising outcomes and successful applications should be continually involved or adapted.

Some experts argue that examples of effective prevention and control are of high value to health policy, of higher value than efficacy data produced by clinical trials on single interventions that have low generalizability to whole health systems.

Impact of Climate Change on Tropical Diseases

Many current trends regard climate change as a factor influencing the emergence of tropical diseases. This trend focuses on the environmental changes of the last decades, particularly on rising temperatures, and evaluates its potential effects on the prevalence and spread of various animal and human pathogens. Temperature influences several pathogen characteristics, such as development time, maturation, reproduction of the pathogen inside the vectors, and the extrinsic incubation period, affecting the transmission patterns.

Moreover, temperature also influences the survival of vectors, or immunity of hosts and reservoirs, thus inducing changes in the vector's and the reservoir's behaviour. A well-known example has been recently provided by a study on the adaptation and survival capacities of mosquitoes in a changing environment. Many research results, although not validated yet, consider mosquitoes as the complex elements of transmission systems, highlighting their potential to adapt to temperature changes, and consequently to have malaria outbreaks in previously temperate regions.

Two extensive reviews on this matter present these mechanisms in detail, analyzing and describing historical cases of emerging infectious diseases. Examples include dengue fever, which emerged in Latin America, West Nile fever, which appeared in the USA, and visceral leishmaniasis, affecting especially the poor populations in Europe.

The socio-economic aspects of tropical disease spread by climate changes are evaluated in an analysis, which describes the arthropod vector-borne diseases and stresses the impact of altered climatic extremes on the cycles of these arboviruses or arboviral zoonoses: increased rainfall, flooding, and storm frequency lead to an augmentation of climate-sensitive vectors, human populations at risk of infection, and disease transmission rates. The pathogens can be directly transmitted to humans by a vector or indirectly by one or more reservoir hosts.

To prevent the spread of these arthropod-borne diseases, the populations need to be protected with safety measures by controlling the rise in vectors and jointly increasing the population understood as bio-ecological changes in the vegetation cover. These responses require action by the public sector so an insurance policy can be introduced, designed to adapt to changing temperatures and rainfall for various regions.

Biological, phytochemical, and physical measures, including the development of safer and more bio-pesticides or higher yields of plants in the programs, may be of interest. To increase the potential of research to prevent the spread of vector-borne diseases by viremia, however, we recommend further climate and health study research in human populations.

It is predicted that climate change will bring significant temperature changes and may have an impact on the African region in the coming years, which makes the possibility of expanding the areas of disease transmission high.