Schistosomiasis and soil-transmitted helminthiases: progress report, 2021

Overview

Schistosomiasis and soil-transmitted helminthiases (STH) are neglected tropical diseases (NTDs) caused by infections with worms. Schistosomiasis is caused by 6  species of trematode: Schistosoma guineensis, S. haematobium, S. intercalatum, S. japonicum, S. mansoni and S.  mekongi. The predominant causative organisms are S. haematobium and S.  mansoni. People are infected by schistosomes transmitted during contact with water contaminated with human excreta containing parasite eggs. A snail host must be present in the water to allow the parasite to complete its life cycle. Groups at risk for schistosomiasis are preschool-aged children (pre-SAC), school-aged children (SAC), adults in certain occupational groups, women who are in contact with infected water for domestic activities and entire communities in high-risk areas. The disease manifests in intestinal and urogenital forms. Intestinal schistosomiasis usually results in diarrhoea and blood in stools; enlargement of the liver and of the spleen and portal hypertension are common in advanced cases.

Urogenital schistosomiasis is characterized by the presence of blood in the urine. Chronic infection results in fibrosis of the bladder and ureter that can evolve to hydronephrosis and create conditions for bladder cancer. In women, urogenital schistosomiasis may cause vaginal bleeding, pain during sexual intercourse and nodules in the vulva, now described as female genital schistosomiasis.

STH are caused by Ascaris lumbricoides (roundworms), Trichuris trichiura (whipworms), Necator americanus and Ancylostoma duodenale (hookworms) and are transmitted by contact with soil infected by human excreta. Groups at risk for STH are pre-SAC, SAC and women of reproductive age (WRA), who are in particular need of micronutrients. STH adversely affect nutritional status and impairs cognitive development in children.

WHO recommends integrated approaches to the control and elimination of schistosomiasis and STH: preventive chemotherapy (PC), consisting of periodic administration of anthelmintic medicines (praziquantel for schistosomiasis and albendazole or mebendazole for STH), improvement of water, sanitation and hygiene (WASH) and behaviour change, snail control and environmental management for schistosomiasis. When schistosomiasis and STH are co-endemic, praziquantel and albendazole (or mebendazole) may be administered together safely.

New guideline for human schistosomiasis control and elimination

In February 2022, WHO issued a new guideline for the control and elimination of human schistosomiasis.2 WHO recommends an integrated approach, combining extension of PC to all people at risk from 2 years of age in communities with a ≥10% prevalence, treatment in health facilities, snail control and WASH to control and eliminate schistosomiasis as a public health problem. The availability of praziquantel in health facilities and treatment of all infected individuals is also recommended. The number of people treated in health facilities should be reported separately from PC. The guideline also provides recommendations on verification of the interruption of schistosomiasis transmission.