Neglected tropical diseases (NTDs) are so called because they are generally afflicting the world’s poor and from past have not received as much attention as other diseases. These diseases tend to thrive mostly the developing regions of the world, where water quality, sanitation, and access to health care are substandard. It is estimated that over 1 billion people are infected with NTDs, with a further 1 billion at risk. The infectious agents for NTDs can be viruses, bacteria, protozoa, helminth parasites.
Some of the common characteristics of NTDs are:
- They afflict the poorest people- those without access to the safe water, sanitation, and basic health services required in order to protect themselves against infection by bacteria, viruses and other pathogens. High-income groups are rarely affected.
- Many are chronic, slowly developing conditions that become progressively worse if undetected and untreated. The damage they cause can be irreversible.
- They can cause severe pain and life-long disabilities, with long-term consequences for the person and also for family members who have to care for the person.
- People with NTD are often stigmatized and excluded from society, and this can affect their mental health.
All the 17 neglected tropical diseases as defined by the World Health Organization (WHO) are:
- Buruli ulcer: Buruli ulcer is a chronic debilitating disease caused by Mycobacterium ulcerans.At least 33 countries with tropical, subtropical and temperate climates have reported Buruli ulcer in Africa, South America, and Western Pacific regions. In Australia, an increasing number of cases have been reported since 2013.
- Chagas disease: About 6 million to 7 million people worldwide, mostly in Latin America, are estimated to be infected with Trypanosoma cruzi, the parasite that causes Chagas disease.
- Dengue/severe dengue: Dengue is a mosquito-borne viral infection. The infection causes a flu-like illness and occasionally develops into a potentially lethal complication called severe dengue. Severe dengue is a leading cause of serious illness and death among children in some Asian and Latin American countries.
- Dracunculiasis: Dracunculiasis is a crippling parasitic disease on the verge of eradication. The disease is usually transmitted when people who have little or no access to improved drinking water sources swallow stagnant water contaminated with parasite-infected water-fleas (Cyclops) that carry infective guinea-worm larvae.
- Food-borne trematodiases: Foodborne trematodiases cause 2 million life years lost to disability and death worldwide every year. Foodborne trematodiases are most prevalent in East Asia and South America.
- Human African trypanosomiasis: This occurs in 36 sub-Saharan Africa countries where there are tsetse flies that transmit the disease.
- Human echinococcosis: Human echinococcosis is a parasitic disease caused by tapeworms of the genus Echinococcus. Humans are infected through ingestion of parasite eggs in contaminated food, water or soil, or through direct contact with animal hosts.
- Leishmaniasis: Leishmaniasis is caused by the protozoan Leishmania parasites which are transmitted by the bite of infected female phlebotomine sandflies.
- Leprosy: Leprosy is a chronic disease caused by a bacillus, Mycobacterium leprae.
- Lymphatic filariasis: Lymphatic filariasis impairs the lymphatic system and can lead to the abnormal enlargement of body parts, causing pain, severe disability, and social stigma. 856 million people in 52 countries worldwide remain threatened by lymphatic filariasis and require preventive chemotherapy to stop the spread of this parasitic infection.
- Onchocerciasis: Onchocerciasis, commonly known as “river blindness”, is caused by the parasitic worm Onchocerca volvulus. It is transmitted to humans through exposure to repeated bites of infected blackflies of the genus Simulium.
- Rabies: Rabies is a vaccine-preventable viral disease which occurs in more than 150 countries and territories. Dogs are the main source of human rabies deaths, contributing up to 99% of all rabies transmissions to humans.
- Schistosomiasis: Schistosomiasis is an acute and chronic disease caused by parasitic worms. People are infected during routine agricultural, domestic, occupational, and recreational activities, which expose them to infested water.
- Soil-transmitted helminthiases: Soil-transmitted helminth infections are caused by different species of parasitic worms. Approximately 1.5 billion people are infected with soil-transmitted helminths worldwide.
- Taeniasis/cysticercosis: Taeniasis is an intestinal infection caused by adult tapeworms. Solium taeniasis is acquired by humans through the ingestion of tapeworm larval cysts (cysticerci) in undercooked and infected pork.
- Trachoma: Trachoma is a disease of the eye caused by infection with the bacterium Chlamydia trachomatis. It is known to be a public health problem in 41 countries and is responsible for the blindness or visual impairment of about 1.9 million people. In 2016, 190.2 million people lived in trachoma-endemic areas and were at risk of trachoma blindness. Blindness from trachoma is irreversible.
- Yaws: Yaws is a chronic disfiguring and debilitating childhood infectious disease caused by Treponema pallidum subspecies pertenue. The disease affects skin, bone, and cartilage. Humans are currently believed to be the only reservoir, and transmission is from person to person.