Neglected Tropical Diseases
Neglected Tropical Diseases (NTDs) are a defined group of parasitic and bacterial infections that affect over 1 billion people globally, particularly in conditions of poverty.
The human, economic and societal impacts of NTD infections are significant because these diseases can result in disabling chronic conditions, delayed growth and cognitive development, severe social stigma, and lost economic productivity.
In an effort to respond to the public health challenge of NTDs, the World Health Organization (WHO) and other global partner institutions endorsed the London Declaration, a commitment to pursuing control or focal elimination of select NTDs by 2020.
What are soil-transmitted helminths?
Soil-transmitted helminths (STHs) are a group of intestinal parasites that thrive in areas with warm, humid soil and poor sanitation.
STHs are common in tropical and subtropical areas, especially in sub-Saharan Africa, the Americas and East Asia, where some communities do not have access to adequate water and sanitation.
The most common STH parasites are:
Ascaris lumbricoides (roundworm)
This parasite lives in the small intestine, where the female worms can grow up to 30 cm in length. Children are often infected more frequently and with a higher worm burden than adults through contact with soil contaminated with roundworm eggs. Childhood growth can be restricted and severe infections can impair intellectual and cognitive development.
Necator americanus, Ancylostoma duodenale (hookworm)
Hookworm larvae enter the body through skin, before they mature as they travel to the small intestine. They then attach to the wall of the intestine to feed. Children and women of reproductive age are most at risk to the symptoms of hookworm as blood loss can result in iron-deficiency anaemia and malnutrition.
Trichuris trichiura (whipworm)
As with Ascaris lumbricoides, whipworm enters the human body through contact with eggs in the soil. The eggs hatch in the small intestine, then attach to the large intestine causinng blood loss and loss of nutrients. Childhood growth can be restricted and severe infections can impair intellectual and cognitive development.
How is the disease transmitted?
Adult STHs maturing in the intestine produce thousands of eggs a day.
STHs are transmitted when infected people shed eggs in faeces that then contaminate soil or water. The eggs are then ingested by others or actively penetrate their skin as larval worms. The cycle will contine unless transmission is broken.
More information on NTDs
- Buruli ulcer
- Chagas disease
- Dengue and Chikungunya
- Dracunculiasis (guinea-worm disease)
- Foodborne trematodiases
- Human African trypanosomiasis (sleeping sickness)
- Leprosy (Hansen's disease)
- Lymphatic filariasis
- Mycetoma, chromoblastomycosis and other deep mycoses
- Onchocerciasis (river blindness)
- Scabies and other ectoparasites
- Soil-transmitted helminthiases
- Snakebite envenoming
- Yaws (Endemic treponematoses)
Clarke, NE, Clements, ACA, Doi, SA, Wang, D, Campbell, SJ, Gray, D, Nery, SV. (2017) Differential effect of mass deworming and targeted deworming for soil-transmitted helminth control in children: a systematic review and meta-analysis.The Lancet 389 (10066): 287-297.
Uniting to Combat NTDs (2012)
London Declaration on Neglected Tropical Diseases