Introduction

Neglected tropical diseases (NTDs) are a diverse group of tropical infections which are common in low-income populations in developing regions of Africa, Asia, and the Americas. They are caused by a variety of pathogens such as viruses, bacteria, protozoa and parasitic worms (helminths).

WHO has recognized 20 Neglected Tropical Diseases. A summary of each disease is given below:

Buruli ulcer

• Buruli ulcer is caused by the bacterium Mycobacterium ulcerans.
• It is related to the family of organisms that cause tuberculosisand leprosy.
• Risk of mortality is low, although secondary infections can be lethal.
• Morbidity takes the form of deformity, disability, and skin lesions, which can be prevented through early treatment and treated with antibiotics and surgery.
• It is found in Africa, Asia, and Latin America. 

Chagas Disease

• Chagas disease is also known as American trypanosomiasis.
• It is caused by a vector-borne protozoa  and spread by contact with Trypanosoma cruzi infected feces of the triatomine (assassin) bug.
• There are approximately 15 million people infected with Chagas disease.
• The chance of morbidity is higher for immuno-compromised individuals, children, and elderly, but very low if treated early.
• Chagas disease does not kill victims rapidly, instead causing years of debilitating chronic symptoms.
• The protozoan can enter the body via the bug's bite, skin breaks, or mucous membranes. Infection can result from eating infected food and coming into contact with contaminated bodily fluids.
• Symptoms are usually skin chancres, unilateral purplish orbital oedema, local lymphadenopathies, and fever.

Dengue and Chikungunya

• Dengue fever is caused by a flavivirus, and is spread mostly by the bite of the Aedes aegypti
• No treatment for either dengue or severe dengue exists beyond palliative care.
• The symptoms are high fever and flu-like symptoms.
• It is found in Asia, Latin America, and Northern Australia.
• Chikungunyais an arboviral disease transmitted by  albopictus and A. aegypti mosquitoes. The virus was first isolated from an outbreak in Tanzania in 1952. 
• Chikungunya virus is a member of the genus Alphavirus and family Togaviridae. 
• Symptoms, generally appearing 5–7 days after exposure, can be confused with dengue and include fever, rash, headache, joint pain, and swelling.
• The disease mainly occurs in Africa and Asia.

Dracunculiasis

• Dracunculiasisis also known as Guinea-worm disease.
• It is caused by drinking water contaminated by water fleas infected with guinea-worm Approximately one year after infection, a painful blister forms, and one or more worms emerge.
• Dracunculiasis is preventable by water filtration, immediate case identification to prevent the spread of disease, health education, and treating ponds with larvicide.
• An eradication program has been able to reduce prevalence. As of 2014, the four endemic countries are Chad, Ethiopia, Mali, and South Sudan.

Echinococcosis

• Human echinococcosis is a parasitic disease caused by tapeworms of the genus Echinococcus.
• The two most important forms in humans are cystic echinococcosis (hydatidosis) and alveolar echinococcosis.
• Humans are infected through ingestion of parasite eggs in contaminated food, water or soil, or after direct contact with animal hosts.
• Prevention programs focus on deworming of dogs, which are the definitive hosts.
• In the case of cystic echinococcosis preventive measures also include deworming dogs, slaughterhouse hygiene, and public education.

Yaws

• Yaws is a tropical infection of the skin, bones, and joints caused by the spirochete bacterium Treponema pallidum pertenue.
• Yaws is spread by direct contact with the fluid from a lesion of an infected person.
• The disease is most common among children, who spread it by playing together.
• Polymerase chain reaction is the most accurate method of diagnosis.
• No vaccine has yet been found.
• Prevention is, in part, by curing those who have the disease, thereby decreasing the risk of transmission.
• Improving cleanliness and sanitation also decreases spread.
• Treatment is typically with antibiotics, including: azithromycin by mouth or benzathine penicillin by injection.
• Almost 85% of infections occurred in three countries—Ghana, Papua New Guinea, and Solomon Islands.
• The disease only infects humans.

Foodborne trematodiases

• The foodborne trematode infections are all zoonotic, primarily affecting domestic or wild animals, but also transmitted to humans.
• They are acquired by eating food, such as raw fish, contaminated with the larval stages of the parasites. At least 40 million people are thought to be infected.

Human African trypanosomiasis (Sleeping Sickness)

• African trypanosomiasis(African sleeping sickness) is a vector-borne disease, and spread through the bite of the tsetse fly.
• It is caused by infection with protozoan parasites belonging to the genus Trypanosoma.
• It is endemic in 36 sub-Saharan African countries where there are tsetse flies that transmit the disease.
• The most common symptoms are fever, headache, lymphadenopathy, nocturnal sleeping pattern, personality changes, cognitive decline, and coma.
• The disease is always fatal if untreated.

Forms:

1. Trypanosoma brucei gambiense is found in 24 countries in west and central Africa. This form currently accounts for 95% of reported cases of sleeping sickness and causes a chronic infection.
2. Trypanosoma brucei rhodesiense is found in 13 countries in eastern and southern Africa. This form represents under 5% of reported cases and causes an acute infection.

Leishmaniasis

• Leishmaniasis is a parasitic disease caused by the Leishmania parasite. This parasite typically lives in infected sand flies.
• One can contract leishmaniasis from a bite of an infected sand fly.
• The sand flies that carry the parasite typically reside in tropical and subtropical environments. Fatal epidemics have occurred in areas of Asia, East Africa, and South America.
• The three forms of leishmaniasis are visceral (Kala-azar), cutaneous, and mucocutaneous.
• The only method of prevention is a vaccine that is under development and prevention of sandfly bites.

Leprosy/Hansen’s Disease

• Leprosy is an infectious disease caused by a bacillus, Mycobacterium leprae, which multiplies slowly.
• On average, the disease incubation period is 5 years but symptoms may occur within 1 year.
• It can also take as long as 20 years or even more to occur.
• Leprosy mainly affects the skin, the peripheral nerves, mucosa of the upper respiratory tract, and the eyes.
• The bacillus is likely transmitted via droplets, from the nose and mouth, during close and frequent contact with untreated cases.
• Leprosy is curable with multidrug therapy (MDT). Untreated, it can cause progressive and permanent damage to the skin, nerves, limbs, and eyes.
• It is most prevalent in India (69% of cases), Brazil, Indonesia, Nigeria, Democratic Republic of the Congo, Madagascar and East Africa, Mozambique to Ethiopia, Brazil and Nepal.
• The BCG vaccine has some preventative effect against leprosy.

Lymphatic filariasis

• Lymphatic filariasis is also known as elephantiasis.
• Three types of worms are known to cause the disease: Wuchereria bancrofti, Brugia malayi, and Brugia timori, with Wuchereria bancrofti being the most common.[2] These worms damage the lymphatic system.
• Approximately two-thirds of cases are in Southwest Asia and one-third in Africa.
• Lymphatic filariasis is caused by parasitic worms known as filarial worms.
• Most cases of the disease have no symptoms.
• Some people, however, develop a syndrome called elephantiasis, which is marked by severe swelling in the arms, legs, breasts, or genitals.
• The skin may become thicker as well, and the condition may become painful.
• Lymphatic filariasis is rarely fatal. 
• It is a vector-borne disease, caused by nematode worms that are transmitted by mosquitoes.
• It can be treated with cost-effective antihelminthic treatments, and washing skin can slow or even reverse damage.
• Prevention can be achieved by treating entire groups in which the disease exists, known as mass deworming.

Onchocerciasis

• Onchocerciasisis also known as "river blindness".
• Onchocerciasis, is a disease caused by infection with the parasitic worm Onchocerca volvulus.
• It is a vector-borne disease, caused by filarial worm infected blackflies.
• Symptoms include severe itching, bumps under the skin, and blindness.
• It is the second-most common cause of blindness due to infection, after trachoma.
• Over 99 percent of cases are in Sub-Saharan Africa.
• It causes blindness, skin rashes, lesions, intense itching, and skin depigmentation.
• It can be treated with ivermectin.
• It can be prevented by insecticide spraying or preventative dosing with ivermectin.
• The symptoms are generally itching and skin lesions.
• A vaccine against the disease does not exist.
• Prevention is by avoiding being bitten by flies.

Rabies

• A deadly virus spread to people from the saliva of infected animals.
• Rabies is caused by lyssaviruses, including the rabies virus and Australian bat lyssavirus.
• It causes inflammation of the brain in humans and other mammals
• Rabies is usually transmitted through an animal bite, for example, from stray dogs.
• Symptoms include fever, headache, excess salivation, muscle spasms, paralysis and mental confusion.
• There is no specific treatment for rabies. Once symptoms appear, it's nearly always fatal.
• A vaccine can prevent infection.

Schistosomiasis

• Schistosomiasis, also known as snail fever and bilharzia,is a disease caused by parasitic flatworms called schistosomes.
• The urinary tract or the intestines may be infected.
• Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine.
• The disease is spread by contact with freshwater contaminated with the parasites.
• These parasites are released from infected freshwater snails.
• The disease is especially common among children in developing countries, as they are more likely to play in contaminated water.
• It belongs to the group of helminth infections.
• Methods of preventing the disease include improving access to clean water and reducing the number of snails.
• Praziquantel is also the treatment recommended by the World Health Organization for those who are known to be infected.
• Approximately 85 percent of cases are in sub-Saharan Africa.

Soil-transmitted helminthiasis

• Soil-transmitted helminth infections are caused by different species of parasitic worms.
• The three major worm species responsible for soil-transmitted helminthiasisare Ascaris (roundworms), Trichuris (whipworm), the hookworms Necator americanus and Ancylostoma duodenale, and Strongyloides stercoralis.
• They are transmitted by eggs present in human faeces, which contaminate the soil in areas where sanitation is poor.
• Infected children are nutritionally and physically impaired.
• Approximately 1.5 billion people are infected with soil-transmitted helminths worldwide.
• Control is based on periodical deworming to eliminate infecting worms, health education to prevent re-infection, and improved sanitation to reduce soil contamination with infective eggs.
• Safe and effective medicines are available to control infection.
• Soil-transmitted helminthiasis occurs in sub-Saharan Africa, the Americas, China, and East Asia.
• The most common symptoms are anemia, stunted growth, intestinal problems, lack of energy, and compromised physical and cognitive development.
• It can be prevented through hygienically prepared food and clean water, improved sanitation, periodic deworming, and health education.
• The World Health Organization recommends mass deworming without prior diagnosis.

Taeniasis/cysticercosis

• Cysticercosisis a tapeworm larvae infection, while taeniasis is infection with adult tapeworms.
• Both are found in Asia, Africa and Latin America, particularly on farms in which pigs are exposed to human excrement.
• Cysticercosis occurs after ingestion of contaminated food, water, or soil. Cysts and lesions can cause headaches, blindness, seizures, hydrocephalus, meningitis, and dementia.
• Taeniasis is not fatal. It is usually contracted after eating undercooked contaminated pork. Taeniasis has mild symptoms, including abdominal pain, nausea, diarrhea, or constipation.
• Drugs are used to treat both diseases.
• Infection can be prevented through stricter meat-inspection standards, livestock confinement, improved hygiene and sanitation, health education, safe meat preparation, and identifying and treating human and pig carriers.

Trachoma

• Trachoma is an infectious disease caused by bacterium Chlamydia trachomatis.
• The infection causes a roughening of the inner surface of the eyelids.
• This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of the eyes, and eventual blindness.
• Untreated, repeated trachoma infections can result in a form of permanent blindness when the eyelids turn inward.
• It is found in Africa, Asia, Central and South America, Middle East, and Australia.
• The disease disproportionately affects women and children.
• The symptoms are internally scarred eyelids, followed by eyelids turning inward.
• Trachoma is caused by a micro-organism that spreads through eye discharges (on hands, cloth, etc.) and by "eye-seeking flies”
• It is treated with antibiotics. The only known prevention method is interpersonal hygiene.

Chromoblastomycosis and other deep mycoses

• Mycetoma is a chronic disease, which usually affects feet, but any part of the body can be affected.
• The disease is caused by bacterial or fungal infections.
• Mycetoma is characterized by a combination of a painless subcutaneous mass, multiple sinuses and discharge containing grains.
• It usually spreads to involve the skin, deep structures and bone, resulting in destruction deformity and loss of function, which can be fatal.
• The disease commonly affects young adults, mostly males aged between 15 and 30 years, in developing countries.
• People of low socioeconomic status, and manual workers such as agriculturalists, labourers and animal herders, are the most susceptible.

Scabies

• Scabies is caused by infection with the female mite Sarcoptes scabiei.
• The mite is an ectoparasite. The mite burrows into the skin to live and deposit eggs.
• The symptoms of scabies are due to an allergic reaction to the mites.
• Scabies is usually spread by direct skin contact with an infected person (at least 10 minutes).
• The spread of disease may occur even if the person has not yet developed symptoms.
• Crowded living conditions, such as those found in child-care facilities, group homes, and prisons, increase the risk of spread.
• Areas with a lack of access to water also have higher rates of disease.

Snakebite envenoming

• Snakebite was added to the list in 2017, after years of criticism of the WHO by activists for not making it a priority.
• The greatest burden of snakebite morbidity in India and Southeast Asia.
• Globally, there are an estimated 421,000 envenomings each year (about 1 in 4 snakebites) and 20,000 deaths, but snakebites often go unreported.^[80]

The Case of India

1. The World Health Organization recognizes 20 neglected tropical diseases, of which 12 are present in India. These are:

• Protozoan infections
  • Leishmaniasis
• Helminth infections
  • Taeniasis/Cysticercosis
  • Dracunculiasis(Guinea-worm disease)
  • Echinococcosis
  • Lymphatic filariasis
  • Soil-transmitted helminthiases
• Viral infections
  • Dengue
  • Rabies
• Bacterial infections
  • Leprosy(Hansen's disease)
  • Trachoma
  • Melioidosis
• Fungal infections
  • Mycetoma, chromoblastomycosis, and other deep mycoses
• Ectoparasitic infections
  • Scabies and other ectoparasites
• Others
  • Snakebite envenoming