Schistosomiasis and soil-transmitted helminthiases: progress report, 2020

Overview

Schistosomiasis and soil-transmitted helminthiases (STH) are worm infections in the group of neglected tropical diseases (NTDs). 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 when schistosomes are transmitted during contact with fresh 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 contamination of soil with infected human excreta. Groups at risk for STH are those in particular need of micronutrients: pre-SAC, SAC and women of reproductive age. 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.