Neglected Tropical Diseases (NTDs)
What are NTDs?
Neglected Tropical Diseases (NTDs) are a range of parasitic, bacterial, viral, and fungal infections. NTDs are mainly prevalent in tropical and sub-tropical areas, and mainly affect the poorest people in society. They are grouped together due to their often chronic, disfiguring, and stigmatising impact, their close association with poverty, and their geographic overlap. There are twenty diseases in the portfolio of NTDs (river blindness and lymphatic filariasis are both neglected tropical diseases) categorised by the World Health Organization (WHO) with a series of targets of varying ambition relating to their control, elimination of transmission, elimination as a public health problem by 2030 – and ultimate eradication.
NTDs are found in several countries in Africa, Asia, the Pacific and Latin America, most often in places where people do not have access to clean water or safe ways to dispose of human waste. NTDs impose a human, social and economic burden on over 1 billion people in all countries of the world. The burden is particularly severe in low-income countries and in the most disadvantaged communities in middle-income countries. Eliminating the spread of neglected tropical diseases worldwide would save thousands of lives each year.
Types of ntds
Commonly known as elephantiasis, lymphatic filariasis is a painful infection caused by nematodes (roundworms), which are transmitted through the bites of infected mosquitos. The worm larvae migrate to the lymphatic vessels where they develop into adult worms.
Also known as river blindness, onchocerciasis is a parasitic disease caused by a filarial work transmitted by bites of infected blackflies. In humans, the adult worms produce embryonic larvae that migrate to the skin, eyes, and other organs.
Buruli ulcer is caused by Mycobacterium and is an environmental bacterium that produces a unique toxin – mycolactone – that causes damage to the skin. Early diagnosis and treatment are essential to minimize morbidity and prevent long-term disability.
Chagas disease, also known as American trypanosomiasis, is an illness caused by the protozoan parasite Trypanosoma cruzi. It is mostly transmitted when humans come into contact with faeces and/or urine of infected triatomine bugs, which are blood-sucking.
Dengue and Chikungunya
Dengue and Chikungunya are mosquito-borne viral infections common in warm, tropical climates. The infections are caused by any one of four closely related viruses – dengue is caused by Flavirideae flavivirus and chiungunya by Togaviridae alphavirus.
Guinea-worm disease is caused by the parasitic worm Dracunculus medinesis, which is the largest tissue parasite that affects humans. Guinea-worm disease is transmitted by drinking contaminated water from ponds or shallow, open wells.
Echinococcosis is a parasitic disease that is transmitted when humans ingest parasitic eggs from the tapeworms Echinococcus granulosus and Echinoccocus multilocularis, which are found in the faeces of dogs, foxes, and other carnivores which harbour the adult worms in their intestines.
Foodborne trematode infections
Foodborne trematode infections are caused by a group of parasites that, when ingested by humans via the consumption of contaminated food such as raw fish, crustaceans, or vegetables, cause infection that can result in severe liver and lung disease.
Human African trypanosomiasis (HAT), or sleeping sickness, is caused by trypanosome parasites that are transmitted by tsetse flies. HAT is only found in sub-Saharan Africa, and mostly affects poor rural populations.
The leishmaniases are a group of diseases that are caused by protozoan parasites from over 20 Leishmania species. The parasites are transmitted to humans via the bite of an infected female phlebotomine sandfly.
Leprosy, or Hansen’s disease, is caused by Mycobacterium leprae and is likely transmitted via droplets, from the nose and mouth, during close and frequent contact with untreated cases. Leprosy is curable, and early treatment can prevent disability.
Mycetoma is a progressively destructive inflammatory disease usually of the foot, although any part of the body can be affected. It is caused by certain bacteria and fungi found in soil and water, which may enter the body through a break or wound in the skin.
Rabies is a viral zoonotic disease transmitted through the bite of an infected animal that causes progressive and eventual fatal inflammation of the brain and spinal cord. Rabies is entirely avoidable with vaccines, medicines, and other technologies.
Scabies is an infectious skin disease caused by a mite called Sarcoptes scabiei. The microscopic mites can live on a person’s skin for months, reproducing on the surface and then burrowing into it to lay eggs, which causes an itchy, red rash to form on the skin.
Schistosomiasis, or Bilharzia, is an infection acquired when people come into contact with fresh water infested for the larval forms of parasitic blood flukes, called schistosomes. The microscopic adult worms live in the veins draining the urinary tract and intestines.
Soil-transmitted helminth (STH) infections are transmitted by eggs present in human faeces which, in turn, contaminate soil in areas with poor sanitation. The main species that infect humans are the roundworm (Ascaris lumbricoides), the whipworm (Trichuris trichiura), and hookworms (Necator americanus and Ancylostoma duodenale).
Snakebite envenoming is caused by toxins in the bite of a venomous snake or by having venom sprayed into the eyes by specific species of snakes that have the ability to spit venom as a defence mechanism.
Taeniasis and cysticercosis
Taeniasis and cysticercosis are caused by infection with the tapeworm Taenia solium. Taeniasis is caused by consumption of raw or undercooked, infected pork, and results in an intestinal infection. Cysticercosis is an infection of tissues such as muscles, skin, eyes, and the central nervous system, caused by ingestion of tapeworm eggs.
Trachoma is one of the leading infectious causes of blindness globally. It is caused by an intracellular bacterium called Chlamydia trachomatis and is transmitted by direct or indirect transfer of ocular and nasal discharges of infected people.
Yaws, or endemic treponematoses, is caused by the bacterium Treponema pallidum subspecies pertenue, and is a skin infection resulting in noncancerous lumps (papillomas) and ulcers.
What Causes neglected tropical diseases?
To achieve the elimination of neglected tropical diseases, we need to look at what causes them. Many neglected tropical diseases are vector-borne, and many have an animal reservoir as part of their lifecycle. Controlling the vectors (e.g., mosquitoes or black flies) that transmit these diseases and improving basic water, sanitation and hygiene are highly effective strategies against these NTDs.
Prevention and Treatment Of NTDs
There are five strategies for tackling NTDs:
Preventive chemotherapy is a disease control strategy used in areas endemic for certain neglected tropical diseases (NTDs) and focuses on the delivery of safe and effective drugs for specific target groups. The NTDs for Preventive Chemotherapy (PC-NTDS) is relevant are onchocerciasis, lymphatic filariasis, dracunculiasis, schistosomiasis, soil transmitted helminthes, and trachoma. Preventive Chemotherapy helps decrease the burden of disease, prevent permanent physical impairments, and minimises chronic pain.
Vector ecology and management
Vector ecology and management is the implementation of control measures to target vectors that transmit pathogens that result in infectious diseases. These vectors include mosquitoes, flies, ticks, and bugs, and control methods can include insecticide-treated bed nets and water, sanitation, and hygiene measures.
Veterinary public health and One Health Approaches
This approach acknowledges that the health and well-being of people is connected to the health of animals and the environments in which people and animals live. Ensuring safe living environments for animals and proper health can help prevent transmission of disease from animals to humans.
Water, Sanitation, and Hygiene (WASH)
Many vectors for neglected tropical diseases live in environments where there is unsafe water and inadequate sanitation and hygiene. Safe storage of water, draining or treating stagnant water, and ensuring appropriate sanitation and hygiene facilities and interventions can help reduce exposure to disease-transmitting vectors.
Elimination of Neglected Tropical Diseases
In 2020, the World Health Organization approved a revised Roadmap for NTDs 2021-2030, which aims to strengthen the global response via three important shifts:
- Stronger accountability by shifting from process to impact indicators
- Integrated approaches that shift away from vertical programming
- Stronger country ownership