Soil-transmitted helminth infections are among the most common infections worldwide and affect the poorest and most deprived communities. They are transmitted by eggs present in human faeces which in turn contaminate soil in areas where sanitation is poor.
The main species that infect people are the roundworm (Ascaris lumbricoides), the whipworm (Trichuris trichiura) and the hookworms (Necator americanus and Ancylostoma duodenale.
Soil-transmitted helminth infections are widely distributed in all WHO Regions. Intestinal worms produce a wide range of symptoms including intestinal manifestations (diarrhoea, abdominal pain), general malaise and weakness. Hookworms cause chronic intestinal blood loss that result in anaemia.
Latest estimates indicate that more than 880 million children are in need of treatment for these parasites.
WHO’s control interventions are based on the periodic administration of anthelminthics to groups of people at risk, supported by the need for improvement in sanitation and health education.
WHO recommends annual treatment in areas where prevalence rate of soil-transmitted helminthiases is between 20% and 50%, and, a bi-annual treatment in areas with prevalence rates of over 50%.
Morbidity and symptoms
Morbidity is directly related to worm burden: the greater the number of worms in the infected person, the greater will be the severity of disease.
Soil-transmitted helminths impair the nutritional status of those infected in many ways, sometimes causing death by:
- negatively affecting nutritional status (causing intestinal bleeding, loss of appetite, diarrhoea or dysentery, and reducing absorption of micronutrients);
- worsening school performance;
- causing complications that require surgical intervention (i.e. intestinal obstruction and rectal prolapse).
Concomitant infections with other parasite species are frequent and may have additional effects on nutritional status and organ pathology.