Neglected Tropical Diseases (NTDs)

Neglected Tropical Diseases (NTDs) such as Schistosomiasis and Onchocerciasis are normally caused by worms or bacteria and occur in tropical climates. These diseases can be treated very cheaply using a 'rapid impact package' comprising five drugs that need only be taken once a year and do not require refrigeration. Such NTD interventions typically have a range of additional positive side effects. According to our research, two of the most cost-effective charities in this area are the Schistosomiasis Control Initiative and Deworm the World.

THE DISEASES

The term 'neglected tropical diseases' covers 15 diseases that have often been overlooked in the battle against poverty. We believe that fighting these diseases may be among the most cost-effective ways of helping people in the developing world, making this a particularly important area for further research.

The most prevalent of the NTDs are:

SOIL-TRANSMITTED HELMINTHIASIS

STH results from infection by roundworm, whipworm, or hookworm. They are the most common infections in the world and affect the most deprived communities: roundworm infects over 1 billion people, whipworm infects 795 million, and hookworm infects 740 million.

Infection is caused by accidentally ingesting eggs from contaminated soil or by the larvae in the soil actively penetrating the skin. Soil-transmitted helminths produce a range of symptoms including diarrhoea, abdominal pain, general malaise, and weakness. They can affect working and learning capacities and impair physical growth. Hookworms cause chronic intestinal blood loss that can result in anaemia. [1]

SCHISTOSOMIASIS

Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is a parasitic disease caused by flatworms. Larval forms of the parasites, which are released by freshwater snails, penetrate the skin of people exposed to affected water. Symptoms include progressive damage to the bladder, ureters, and kidneys, as well as progressive enlargement of the liver and spleen, intestinal damage, and hypertension. [2]

LYMPHATIC FILARIASIS (LF)

LF (which is commonly known as elephantiasis) is caused by thread-like worms known as filariae, which are spread from human to human by mosquito bites. Once inside the skin, they migrate to the lymphatic system where they cause significant damage and produce millions of offspring. LF is most well known for causing a disfiguring swelling of the limbs or genitals that often leads to disability and social isolation. [3]

ONCHOCERCIASIS

Onchocerciasis, or river blindness , is caused by a certain type of filarial worm. It is transmitted from human to human through the bites of infected blackflies. The larvae form nodules under the skin, where they mature to adult worms. After mating, each female adult worm can release up to 1,000 offspring per day. These move through the body, and when they die they cause a variety of conditions, including blindness, lesions, and intense itching. [4]

TRACHOMA

Trachoma is a bacterial infection. It spreads from person to person through eye, nose and throat secretions, especially in areas where there are water shortages, numerous flies, and crowded living conditions. Infection often begins during infancy or childhood and can become chronic. If left untreated, the infection eventually causes the eyelid to turn inwards, which in turn causes the eyelashes to rub on the eyeball, resulting in intense pain and scarring of the front of the eye. This ultimately leads to irreversible blindness, typically at between 30 and 40 years of age. [5]

THE TREATMENT

The first four of the above diseases are caused by parasitic worms, while Trachoma is bacterial. These conditions can each be treated/prevented by taking the appropriate medication every 6-24 months. People have recently started using a combination of five drugs, known as the 'rapid impact package', which allows all of these diseases to be treated at once.

There are many reasons why the rapid impact packages are so exceptionally cost-effective:

  • The drugs need only be given once a year and treatment throughout one's school years can offer life-long protection.
  • The drugs are cheap to buy at market rates, and are often donated by pharmaceutical companies.
  • The drugs keep for 4 years and do not require refrigeration, which makes distribution easier.
  • The high proportion of people infected, the very low price of the drugs, and the fact that the drugs are safe to take even if one is not infected, mean that everyone in an affected area can be given the drug. Thus there is no need for a potentially costly screening process.
  • There is considerable geographical overlap and co-infection of these diseases, so it is often possible to treat many of them with one package of five drugs.
  • Because these diseases have been neglected in the past, the easiest and most cost-effective interventions have still not been performed.

COST-EFFECTIVENESS

The 'Combination deworming' approach is extremely cost-effective. According to a GiveWell's estimate of the cost per 'life-equivalent' saved through combination deworming is ~$1600-4500. If we consider saving one life to be equal to 30 DALYs, this suggests a cost of around ~$50-150 per DALY.

Reasons to be optimistic about NTD treatment.

There are several reasons to suspect that treating neglected tropical diseases might nevertheless be very cost effective. See our blog post on this topic for a more comprehensive overview.