Neglected tropical diseases (NTDs) affect one in six people worldwide, and more than half of them live in areas where they can become infected. While most NTDs are concentrated in the tropical regions of Asia and Africa, many can be found throughout the world, including wealthy countries like the United States.
The World Health Organization (WHO) officially recognizes at least 21 infections as NTDs, each with its own causes, symptoms, and modes of transmission. However, what they all have in common is that they overwhelmingly affect the poor.
This disease is caused by the bacteria Mycobacterium ulcerans . While it's unclear how humans enter bacteria once they enter the body, they produce a toxin that attacks and destroys human tissue, typically resulting in ulcers on a person's hands or feet.
Antibiotics can help treat the infection, but without them, the disease can lead to lifelong disability or deformity. Although most cases occur in central and western Africa, infections are also found in wealthier countries, including Australia and Japan.
This disease, found mainly in Latin America, is the result of Trypanosoma cruzi , a parasite transmitted by the triatomaceous bug or "kissing bug", an insect that likes to live on muddy walls and thatched roofs that are often found in poor areas. Most people with Chagas disease do not have any symptoms , while those with symptoms can be mistaken for other illnesses , such as the flu .
If left untreated , the parasite can cause a chronic (long-term) infection that can lead to heart problems or death. According to the WHO, about 8 million people worldwide have Chagas disease, including more than 300,000 people in the United States and another 25 million people worldwide are at risk of contracting the disease.
Dengue virus, often referred to as 'withdrawal fever' because of the physical pain it causes, is transmitted by Aedes mosquitoes, the same species that carry West Nile virus, yellow fever, and Zika virus . In severe cases, the virus can cause bleeding from the nose or mouth, a condition called dengue hemorrhagic fever.
Dengue is already endemic in more than 100 countries, and while it is difficult to determine exactly how many people are directly affected (underreporting and misclassification of cases is a problem), a 2013 report estimated between 284 and 528 million dengue infections. every year around the world.
These numbers could increase. By one estimate, more than half the planet could be at risk for dengue fever, and some health officials are bracing for more cases as rising global temperatures expand mosquito habitats and rising mosquitoes of international travel makes it easier for people to carry the virus to new places. where Aedes mosquitoes are already common.
Another mosquito-borne disease, chikungunya , is often mistaken for dengue because it can cause many of the same symptoms as fever, muscle aches, headaches, and skin rashes.
Like dengue, there is no cure or effective cure for the virus, but the disease is not yet widespread. Cases have occurred in more than 60 countries , including the Caribbean and Europe, but most of the time they are limited to parts of Africa and Asia.
This parasitic worm, also known as guinea worm, has a complex life cycle and infects humans through contaminated water. Once inside the body, the worm causes burning, painful ulcers. Infected people often try to get relief by going to water sources, where the worms emerge from the skin to release more larvae, which can lead to more infections.
The Guinea worm has been infecting people for centuries. There are documented cases in the Old Testament Bible, WHO reports, but now they are on the verge of being eradicated thanks to a globally coordinated effort led by the Carter Center. The number of infections dropped from more than 3 million in 1986 to just 30 in 2017.
Getting to this was not easy. Global partners had to muster a lot of political will to obtain the resources necessary to investigate, contain and report suspected cases; and train and mobilize villages to filter unsafe water.
Caused by tiny tapeworms, this disease primarily affects animals, but can spread to humans when humans come in contact with the feces of infected creatures, such as domestic cats and dogs, or livestock such as sheep or goats. This often happens when food (such as berries or vegetables) or water becomes contaminated with parasite eggs, or after touching contaminated fur (such as petting a dog).
Two different classifications of tapeworms can cause this disease, and both can lead to serious illness or death. According to the CDC , the greatest danger to humans is alveolar echinococcosis, which can cause tumors in the liver, brain, and other organs. Another classification, cystic echinococcosis, does not usually cause symptoms in humans, but when it does, it can lead to cysts in vital organs, which can be dangerous but go unnoticed for years.
This group of diseases, also called foodborne flukes, is caused by ingestion of flatworms (also called flukes) in the larval stage. This can happen if food, especially raw fish or shellfish, is not fully cooked. Although the WHO reports that these infections occur mainly in East and Southeast Asia and Central and South America, at least 40 million people are infected worldwide.
African sleeping sickness
Many NTDs are transmitted through animals or pests, and African sleeping sickness (also known as human African trypanosomiasis) is no exception. This parasite is transmitted through the tsetse fly in rural areas of Africa. Once in the bloodstream, the parasite slowly travels to the central nervous system, causing sleep disturbances, sensory disturbances, seizures, and a host of other serious physiological and psychological conditions.
Treatments are available , but they are often complex, difficult to apply, and have some unpleasant side effects. However, if left untreated, the disease is often fatal.
Phlebotomy mosquito leishmaniasis is a parasitic disease of the Leishmania species. Most people infected with the parasite have no symptoms, but leishmaniasis is especially true for those who do.
Infections can manifest in different ways, most commonly skin ulcers (cutaneous leishmaniasis) or more severe visceral leishmaniasis, which can lead to severe weight loss, fever, anemia, or inflammation of the spleen or liver. The latter is very life threatening if left untreated.
Outbreaks of leishmaniasis, which are often found in densely populated areas, have particularly affected conflict zones and refugee groups in recent years.
Leprosy is a chronic infection caused by the bacterium Mycobacterium leprae , best known for the lesions and discoloration it can cause on human skin. If left untreated, the infection can cause lifelong nerve damage or disfigurement.
More than 200,000 cases of leprosy are reported each year, including 150 to 250 cases in the United States, with the majority of infections occurring in South and Southeast Asia. Although they have been affecting humans for millennia, health professionals and researchers are still unsure how bacteria spread, although some believe they can be transmitted through touch and / or respiratory droplets.
Elephantiasis is known to cause severe limb swelling, a painful infection caused by nematode worms (filariae). Microscopic worms enter the human body through mosquito bites and multiply in the human lymphatic system. The swelling, pain, and deformity can be so severe that people are unable to work, and endemic countries (primarily in Southeast Asia and parts of Africa) lose about a billion dollars a year and, in some cases, damage economic activity by up to 88 percent, according to the WHO. .
Global partners are now trying to eradicate the disease by helping endemic countries treat entire populations at risk. Treating people with deworming drugs annually for more than 5 years may be enough to break the cycle of transmission that sustains the infection, but with more than 120 million people infected, there is still a lot of work to do, according to the CDC. do before the disease is completely eliminated.
Mycetoma, Chromoblastomycosis, and Other Deep Mycoses: Little is known about the prevalence of this group of diseases, at least in part because of who it affects: very low-income adults working as laborers, herders, or farmers in developing countries. These workers often walk barefoot and bacteria or fungi are believed to enter the body through open wounds in the skin.
Over time, the infection causes swelling or sores (usually on the foot), which become increasingly debilitating over time. Medications are available to treat the infection, but they are not very good . They are expensive and have many side effects. Surgery is often required to treat fungal infections.
River blindness is the leading cause of preventable blindness worldwide. Disease-causing worms (called filamentous worms or O. volvulus ) are transmitted from person to person through mosquito bites and can live in humans for up to 15 years. An estimated 37 million people are currently infected, almost exclusively in Africa, and those living in rural agricultural areas are the most affected.
River blindness can be successfully treated with a single dose of the drug, but to eradicate the disease, countries must also control the population of mosquitoes responsible for its spread, something that many endemic countries simply cannot afford.
With a vaccine developed more than a century ago, rabies deaths can be nearly 100 percent prevented if the vaccine is given before an infected person begins to show symptoms , a difficult task in areas where there is no good access. to medical care.
Without a vaccine, rabies is almost always fatal, causing tens of thousands of deaths worldwide each year. Most of these deaths occur in Asia and Africa, although the disease occurs in 150 countries around the world and on all continents except Antarctica.
However, the key to reducing rabies mortality is not vaccinating humans, but vaccinating dogs. The vast majority of human rabies cases are the result of rabid dog bites, which is why the United States spends more than $ 300 million a year on rabies prevention, primarily on dog vaccines.
These efforts have been highly successful: According to the CDC, only 23 human cases of rabies have been reported in the United States during the last decade. But to eradicate the disease on the planet, it is necessary to apply the same strategy on a global scale.
Scabies and other ectoparasites were added to the WHO NTD list in 2017, scabies is extremely common in developing countries and affects more than 200 million people worldwide on any given day, mainly in the regions low-income tropical trees.
It is caused by parasitic mites that burrow into the skin to lay eggs. This triggers the body's immune response, causing itching and rashes. Scratching the affected areas can also lead to bacterial skin infections, which can complicate the condition or lead to more serious problems within the body.
The most vulnerable groups affected by scabies are young children and the elderly who live in poor and overcrowded areas, where mites can be transmitted from person to person.
Schistosomiasis (snail) kills about 280,000 people annually in Africa alone, making it the world's deadliest NTD. Millions more people suffer severe physical and mental disabilities as a result of the infection.
The disease is caused by parasites (worms) that live in fresh water, where some snails are also infected. When children swim or fish in the water, or people come in contact with the water during their daily activities, the worm larvae penetrate the skin and enter the blood vessels, where the adult worms eventually release their eggs.
Schistosomiasis is a disease of poverty. Without access to clean water or adequate toilets, people continue to ingest the parasite and shed its eggs through feces, contributing to the spread of the disease.
Children with long-term or recurrent infections are often anemic or malnourished, which can cause lifelong learning difficulties and contribute to a vicious cycle of poverty.
Like schistosomiasis, soil-borne helminths (such as hookworms, roundworms, or whipworms) disproportionately affect the poor. These worms live in the intestines of infected people, who then excrete their eggs in the feces.
In places without toilets or latrines, it is not uncommon for people to defecate on the ground or in shallow pits, where eggs can contaminate water or food sources, causing new infections or reinfections. Hookworm larvae can also pierce the foot when people walk barefoot on contaminated soil. If these communities had access to basic sanitation, much of the transmission cycle would be interrupted.
Currently, more than 1 billion people are infected with these intestinal parasites and more than 4 billion (or more than half of the world's population) are at high risk of infection, and almost all of them live in poor areas. The WHO estimates that more than 880 million children need medications for these worms to prevent the potentially serious consequences of infections, including developmental delay, vitamin A deficiency or poor growth.
Venomous snake bite
The WHO added snake venom poisoning to its NTD list in June 2017. Of the more than 3,000 species of snakes that exist in the world, the WHO considers 250 of them dangerous. These snakes live in 160 countries and their poisonous bites kill 81,000 to 138,000 people worldwide each year, as well as hundreds of thousands of amputations and disabilities.
These statistics can greatly underestimate the true magnitude of the problem because many at-risk communities, especially in rural and agricultural areas, do not have access to medical care or prefer to receive treatment from non-medical sources due to cultural beliefs.
Teniosis and cysticercosis
These two conditions are caused by the same tapeworm: T. solium . Infection by an adult tapeworm in the human intestine (taeniasis) is much less dangerous than infection by a worm in the larval stage (cysticercosis).
When humans inadvertently ingest worm eggs (usually through contaminated food or water, or as a result of poor hygiene), the worms hatch into larvae, which can form potentially harmful cysts throughout the body, including the eyes. , the muscles and the central nervous system. system. …
Trachoma, the leading cause of infectious blindness in the world, currently affects some 84 million people worldwide, many of whom are children. This painful and debilitating condition is the result of repeated infections with the bacteria Chlamydia trachomatis which, if left untreated, can cause the eyelids to collapse inward. Over time, when the eyelashes scratch the eyeball, irreversible damage occurs and, in some cases, irreversible blindness.
The bacteria can spread rapidly in overcrowded areas where there is no access to clean water or toilets, especially among young children and their caregivers who live in extreme poverty. Some rural communities report that 60 to 90 percent of their children are infected with this bacteria, according to the CDC.
Another disease that can cause irreversible disability in children is yaws, a chronic skin condition that is closely related to poverty. A disease caused by the bacteria Treponema pallidum (a close relative of syphilis) causes bumps and sores on the skin that are highly contagious.
Yaws is very easy to treat. A single dose of an inexpensive antibiotic is sufficient. But if left untreated, it can affect the bones and cartilage and lead to permanent disfigurement or disability. The vast majority (75-80 percent) of those infected are children under the age of 15, most of whom live in rural and / or poor areas without medical care.