Current WHO guidelines
Current WHO STH guidelines recommend delivering preventative chemotherapy - albendazole or mebendazole - via
- mass drug administration (MDA) campaigns
- targeting pre-school and school-age children
- living in areas where the baseline prevalence of any STHs infection is 20% or higher among children.
The purpose of this strategy is to reduce STH-associated morbidity by reducing STH worm burdens in children.
However, the targeted approach is unlikely to break transmissions of STHs in the community because adults and other untreated community members may act as reservoirs for STHs infections, contributing to ongoing reinfection of treated children.
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
- roundworm (Ascaris lumbricoides)
- hookworm (Necator americanus, Ancylostoma duodenale)
- whipworm (Trichuris trichiura).
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 and are ingested by others or actively penetrate their skin as larval worms.
Additionally, hookworm eggs can hatch in the soil and release larvae that mature and are capable of actively penetrating the skin of bare feet.
What are the symptoms?
Adult worms and eggs infect a person's gut reducing the uptake of nutrients and vitamins leading to
- stunted growth
- impaired cognitive development
- an increased susceptibility to other infectious diseases
Preventive chemotherapy to control soil-transmitted helminth infections in at-risk population groups World Health Organisation, September 17 2017.
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.