Neglected tropical diseases (NTDs), such as dengue, lymphatic filariasis, trachoma, and leishmaniasis, are called "neglected," because they generally afflict the world's poor and historically have not received as much attention as other diseases. NTDs tend to thrive in developing regions of the world, where water quality, sanitation, and access to health care are substandard. However, some of these diseases also are found in areas of the United States with high rates of poverty.

Neglected tropical diseases, take a tremendous toll on global health. The World Health Organization estimates that more than one billion people — approximately one-sixth of the world's population — suffer from at least one NTD. While NTDs rarely lead to death, they can cause significant disability that persists for a lifetime, including fatigue, blindness, and disfigurement. Sufferers miss school, are unable to work, or are too embarrassed to seek medical care. By diminishing quality of life and opportunities to succeed, NTDs can reinforce the cycle of poverty among the world's disadvantaged populations.

• Neglected tropical diseases (NTDs) are widespread in the world’s poorest regions, where water safety, sanitation, and access to health care are substandard.
• An estimated 1 billion people—approximately one-sixth of the world’s population—suffer from at least one NTD.
• NTDs are called “neglected” because they generally are not considered public health problems in wealthier nations and historically have not received as much attention as other diseases.
• Some NTDs are found in parts of the United States, particularly among impoverished minorities.
• NTDs comprise several diseases that have a range of effects, from extreme pain to permanent disability to death. Here are some examples:
  • Ascariasis: Caused by the soil-transmitted roundworm Ascaris lumbricoides, it can impair growth and cognition.
  • Buruli ulcer: Caused by Mycobacterium ulcerans, it can lead to massive skin ulceration.
  • Chagas disease (American trypanosomiasis): Caused by a parasite transmitted by blood-sucking “assassin bugs,” it can lead to swollen lymph nodes and organ damage.
  • Dracunculiasis (guinea-worm disease): Contracted by drinking water contaminated with larvae of the parasitic worm Dracunculus medinensis, it causes painful, erupting blisters as the worms emerge through the skin.
  • Hookworm: Often contracted by walking barefoot on soil contaminated by feces, hookworm infections can causes blood loss and anemia.
  • Human African trypanosomiasis (sleeping sickness): Caused by a parasite transmitted from tsetse flies, it can lead to fever, weakness, stiffness, and death.
  • Leishmaniasis: A parasitic disease transmitted by infected sand flies, it can cause skin ulcers or lesions and swelling of the spleen and liver.
  • Leprosy (Hansen’s disease): A chronic infectious disease caused by bacteria, it can lead to permanent damage to the skin, nerves, limbs, and eyes.
  • Lymphatic filariasis (elephantiasis): A parasitic worm disease spread from human to human by mosquitoes, it can lead to disfiguring swelling of the legs, scrotum, and breast.
  • Onchocerciasis (river blindness): A parasitic worm disease spread from by infected black flies, it can cause extreme itching, blindness, and skin lesions.
  • Schistosomiasis: A parasitic worm disease transmitted by fresh water snails, it can lead to blood in the urine, impaired growth, and malfunctioning of the kidney, liver, and spleen.
  • Trachoma: Caused by the bacterium Chlamydia trachomatis, it can lead to scarring of the inside of the eyelid and blindness.
  • Trichuriasis: Contracted by ingesting soil or vegetables contaminated with feces containing whipworm eggs, it can cause dehydration and anemia and impair growth and cognition.
• Despite their pervasiveness around the world, most NTDs are relatively easy to treat and can be prevented.

Neglected tropical diseases (NTDs) comprise several diseases that have a range of effects, from extreme pain to permanent disability to death. Here are some examples:

Ascariasis

Caused by a parasitic roundworm called A​scaris lumbricoides, ascariasis is common in areas where sanitation and hygiene are poor. The disease often causes only mild symptoms (or no symptoms at all), but in cases of high worm infestation, ascariasis can lead to severe abdominal pain, vomiting, restlessness, and sometimes death.

Buruli ulcer

Caused by Mycobacterium ulcerans, an organism from the same family of bacteria that causes tuberculosis and leprosy, Buruli ulcer can lead to massive skin ulceration, usually on the legs or arms. If untreated, the disease can spread to the bones and cause long-term disability.

Chagas' disease (American trypanosomiasis)

Caused by a parasite transmitted by blood-sucking “assassin bugs,” Chagas' disease can lead to swollen lymph nodes and organ damage.

Dracunculiasis (guinea-worm disease)

Contracted by drinking water contaminated with larvae of the parasitic worm Dracunculus medinensis, dracunculiasis can cause painful, erupting blisters as the worms emerge through the skin.

Dengue fever

An infectious disease carried by mosquitoes and caused by any of four related dengue viruses. Formerly called "break-bone" fever, dengue can cause severe joint and muscle pain. Left untreated, patients may experience hemorrhage and shock, leading to death.

Hookworm

A common parasitic roundworm infection, hookworm disease can be contracted by walking barefoot on soil contaminated by feces. Symptoms of the disease include diarrhea, abdominal pain, and nausea. Chronic, or long-lasting, hookworm infections can cause severe blood loss and anemia.

Human African trypanosomiasis (sleeping sickness)

Caused by a parasite transmitted from tsetse flies, human African trypanosomiasis can lead to headaches, fever, weakness, and stiffness. If untreated, the parasite migrates to the central nervous system, causing seizures, psychiatric disorders, and ultimately death.

Leishmaniasis

A parasitic disease transmitted by infected sand flies, leishmaniasis can cause skin ulcers or lesions and swelling of the spleen and liver.

Leprosy (Hansen's Disease)

A chronic infectious disease caused by mycobacteria, leprosy can lead to permanent damage to the skin, nerves, limbs, and eyes.

Lymphatic filariasis (elephantiasis)

A parasitic worm disease spread from human to human by mosquitoes, lymphatic filariasis can lead to disfiguring swelling of the legs, scrotum, and breast.

Onchocerciasis (river blindness)

A parasitic worm disease spread by infected black flies, onchocerciasis can cause extreme itching, blindness, and skin lesions.

Schistosomiasis

A parasitic worm disease transmitted by fresh water snails, schistosomiasis can lead to blood in the urine, impaired growth, and malfunctioning of the kidney, liver, and spleen.

Trachoma

Caused by the bacterium Chlamydia trachomatis, trachoma can lead to scarring of the inside of the eyelid. If untreated, the disease can lead to irreversible blindness.

Trichuriasis (whipworm disease)

Contracted by ingesting soil or vegetables contaminated with feces containing whipworm eggs, trichuriasis can cause dehydration and anemia and impair growth and cognition.

Several neglected tropical diseases (NTDs) are transmitted by infected insects. For example, Chagas disease is transmitted by the triatomine, or “kissing,” bug and can lead to life-long cardiac problems; leishmaniasis is transmitted by infected sand flies and can lead to sores that cause permanent scarring; onchocerciasis is transmitted by infected black flies and can lead to blindness; and dengue fever, which can lead to circulatory failure, and lymphatic filariasis, which can lead to extreme swelling of the genitalia or limbs, are both transmitted by infected mosquitoes.

Other NTDs are transmitted through consumption of water or food that harbors parasites. Guinea-worm disease, fascioliasis, and schistosomiasis are examples of NTDs that infect people through contaminated water or food.

Most NTDs are not transmitted from person to person, although there are exceptions. Leprosy—although not highly contagious—can be transmitted through respiratory droplets in coughs and sneezes and can lead to thick skin lesions and nerve damage. Trachoma, which can lead to blindness, can be transmitted through personal contact and the sharing of personal items that harbor the bacteria.

Symptoms of neglected tropical diseases (NTDs) vary dramatically from disease to disease. Some immediately present symptoms such as fever, aches, rash, sores, or swelling of the lymph nodes or at the site of infection.

Some NTDs, such as sleeping sickness, leprosy, and guinea-worm disease, may not present symptoms for one or several years.

If treated, most NTDs are not fatal. But if left untreated, NTDs can lead to serious and chronic conditions and can even cause death. Because NTDs generally occur in regions with poor access to health care, many infected people likely die from their infections before the infections are ever reported.

Many neglected tropical diseases (NTDs) can be diagnosed in the laboratory using simple and inexpensive microscopy, serology, and culture techniques. Some diseases, particularly those caused by parasites, can be detected in stool samples.

While most NTDs can be recognized and diagnosed in a clinical setting by trained health professionals, many are not because those infected are typically poor and do not have access to quality health care and lab facilities. In these cases, creating easier access to better facilities would allow affected people to receive treatment for NTDs more quickly—thus avoiding many complications of advanced disease.

The good news about neglected tropical diseases (NTDs) is that many are treatable with existing drugs. Certain treatments are easy to administer and do not require health professionals. The bad news is that, while drug treatments are available for many NTDs, they don’t often reach the people most in need.

Several governmental and non-governmental organizations work to help strengthen health infrastructure and deliver drugs in regions afflicted by NTDs. For example, the World Health Organization Division of Control of Neglected Tropical Disease helps organize funding and relief efforts in these areas. Some drug companies also donate medications to help treat NTDs.

As with tuberculosis and malaria, drug resistance is becoming an issue with NTDs. For example, praziquantel has been used since the 1980s to treat the neglected parasitic worm disease schistosomiasis. Public health officials fear that the worms are evolving resistance to the drug and have underscored the need for further research and development of new and improved treatments for the disease.

Neglected tropical diseases (NTDs) are largely preventable, even without vaccines. Clean water, sanitary food handling, and good hygiene can prevent diseases such as guinea-worm disease, schistosomiasis, soil-transmitted helminthiasis, and trachoma.

Vector-borne NTDs—those that are spread by worms, flies, mosquitoes, or other hosts—can be prevented through control of the vectors themselves. This can include mass spraying of insecticides in areas where the vectors breed or gather, killing them before they become parasite carriers. Scientists are also exploring ways to genetically alter the vectors so that they cannot carry the parasite. The genetically altered vectors would then be released into the population to breed and spread their genetic abnormalities to future generations.

Educating the at-risk population is also an important aspect of NTD prevention. By controlling environmental factors that invite NTDs, people can reduce their risk. For instance, eliminating areas of standing water, where mosquitoes like to breed, will reduce the risk of mosquito-borne diseases, or sleeping under a treated bed net will reduce the risk of diseases carried by flies that circulate at night. Travelers to areas where insect-borne NTDs are widespread should take care to wear protective clothing, use bug repellant, and sleep under a treated bed net.

Neglected diseases are conditions that inflict severe health burdens on the world's poorest people and are often overlooked by drug developers or by others instrumental in drug access.

What is a neglected disease?

Neglected diseases are conditions that inflict severe health burdens on the world's poorest people. Many of these conditions are infectious diseases that are most prevalent in tropical climates, particularly in areas with unsafe drinking water, poor sanitation, substandard housing and little or no access to health care.

Why do we call them neglected?

Diseases are said to be neglected if they are often overlooked by drug developers or by others instrumental in drug access, such as government officials, public health programs and the news media. Typically, private pharmaceutical companies cannot recover the cost of developing and producing treatments for these diseases.

Another reason neglected diseases are not considered high priorities for prevention or treatment is because they usually do not affect people who live in the United States and other developed nations.

Neglected diseases also lack visibility because they usually do not cause dramatic outbreaks that kill large numbers of people. Rather, such diseases usually exact their toll over a longer period of time, leading to crippling deformities, severe disabilities and/or relatively slow deaths.

How many people are affected?

The World Health Organization (WHO) estimates that more than 1 billion people — one-sixth of the world's population — suffer from one or more neglected diseases.

The diseases are most heavily concentrated in low-income nations in Africa and Latin America. In addition, neglected diseases take a heavy toll in parts of Asia and the Middle East, although the range of diseases is narrower. Some of these diseases also are occasionally found in areas of the United States with high rates of poverty.

What are some examples?

The most common type of neglected diseases are tropical diseases. Many neglected tropical diseases are caused by parasites, which are spread by insects or contact with contaminated water or soil. Examples of these parasitic diseases include:

• African trypanosomiasis. Commonly called sleeping sickness, this disease is caused by a parasitic microbe transmitted by tsetse flies. If untreated, the parasite migrates to the central nervous system, causing seizures, mental disorders and, ultimately, death. As many as 70,000 people are infected in Central and East Africa.

• American trypanosomiasis. Commonly called Chagas disease, this disease is caused by a parasitic microbe transmitted by blood-sucking bugs. It can cause organ damage. The parasite infects about 13 million people, mostly in Latin America.

• Hookworm. Human hookworm infection is caused by intestinal worm parasites transmitted to humans from contaminated soil. It causes internal blood loss and is the world's leading cause of anemia and protein malnutrition, particularly in pregnant women and children. More than half a billion people in poverty-stricken areas of Africa, Latin America, Southeast Asia and China are infected.

• Leishmaniasis. This disease is caused by a parasitic microbe transmitted by sand flies. It can cause skin lesions and swelling of the spleen and liver. More than 12 million people are infected in Africa, Asia, Europe and the Americas.

• Lymphatic filariasis. Commonly called elephantiasis, this parasitic worm disease is spread by mosquitoes. It can lead to disabling swelling of the legs and other body parts. About 120 million people are infected throughout Asia, Africa, the Western Pacific, South America and parts of the Caribbean.

• Malaria. This disease is caused by a parasitic microbe spread by mosquitoes. Each year, malaria infects at least 300 million people living in tropical regions. It can cause brain damage or death if red blood cells infected with malaria parasites build up in the brain's blood vessels. The annual death toll is about 1 million people, many of whom are children under age 5 and pregnant women.

• Onchocerciasis. Commonly called river blindness, this parasitic worm disease is spread by black flies. It can cause extreme itching, sores on the skin and blindness. The parasite infects about 18 million people, mostly in Africa, but also in Latin America.

• Schistosomiasis. Also known as bilharzia or snail fever, this parasitic worm disease is transmitted by snails that live in fresh water. It can impair growth, cause severe anemia and lead to kidney and liver malfunctions. More than 200 million people are infected, mostly in Africa and Asia.

Other neglected tropical diseases are caused by bacteria. Examples of bacterial diseases include:

• Buruli ulcer. This disease can cause massive open sores on the legs and arms. If untreated it can spread to the bones. The disease has been reported in 30 countries, but it is not known how many people it infects.

• Trachoma. This disease can scar the inside of the eyelid. If untreated, it can lead to blindness. About 80 million people worldwide are infected. The disease occurs mostly in the poorest regions of Africa, Asia and the Middle East, but also has been reported in some parts of South America and Australia.

• Yaws. This disease is a bacterial infection that affects mainly the skin, bone and cartilage. While rarely fatal, yaws can lead to deformities and disability. It is not known how many people have the disease. However, tens of thousands of cases have been reported in Ghana, Indonesia and Papua New Guinea, with most occurring in children younger than 15.

What can be done to prevent them?

Specific prevention strategies vary from disease to disease. But experts agree that a good way to head off many neglected diseases is to provide people with safe sources of drinking water, good sanitation, adequate housing and access to health care.

For diseases that are spread by insects, simple measures such as pesticides or hanging nets around beds may help to prevent or reduce the risk of getting infected. For diseases transmitted by snails and other organisms that live in streams and rice paddies, people can reduce their risk by not bathing or wading in water at high risk of contamination. For some diseases caused by bacteria, an effective precaution may be to boil water used for drinking, cooking and hand washing.

Other measures involve giving people medications that will prevent infection or greatly minimize the impact of infection if it does occur. Common examples are the anti-malarial drugs that many take to ward off malaria infections. Still, even at a cost of less than 50 cents a day, such drugs remain too expensive for many poor people.

In addition to drugs, researchers are working to develop vaccines that would spur the body's own immune system to ward off disease-causing agents. But major roadblocks remain. In addition to significant scientific challenges, many drug companies have expressed concerns about how people living in the world's poorest areas would be able to pay for vaccines.

How can neglected diseases be treated?

Many people with neglected diseases do not receive proper treatment. One reason is that, due to lack of health care services, they will not be diagnosed with a disease until it is in an advanced stage that is difficult to treat. Even if people are diagnosed early, many cannot afford drugs known to be effective against the disease. Finally, no good treatments exist for some neglected diseases.

Much needs to be done to address all of these challenges. Public health experts are trying to develop better ways of delivering health messages and services to low-income people. They are also educating officials in developing nations about why it makes good economic sense to provide health care and treatments to people suffering from neglected diseases.

For their part, medical researchers are searching for less costly drugs for neglected diseases, and working to develop new drugs for diseases that lack treatments. In recent years, public and non-profit groups have partnered with drug firms in efforts to produce less costly and more effective treatments. Some progress has been made, but the number of drugs developed specifically for neglected diseases still trails behind drugs for other disorders.