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Weekly Epidemiological Record (WER), 14 December 2018, vol. 93, no. 50 (pp. 681–692) [EN/FR]

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681 Schistosomiasis and soiltransmitted helminthiases: numbers of people treated in 2017

Sommaire

681 Schistosomiase et géohelminthiases: nombre de personnes traitées en 2017

Schistosomiasis and soil-transmitted helminthiases: numbers of people treated in 2017

Background

Schistosomiasis is caused by 6 species of trematodes of the genus Schistosoma: S. guineensis, S. haematobium, S. intercalatum, S. japonicum, S. mansoni and S. mekongi. The predominant causes of disease are S. haematobium and S. mansoni. Infection occurs when schistosomes are transmitted during contact with fresh water contaminated with human excreta containing parasite eggs. A snail hosts must be present in the water to allow the parasite to complete its life cycle. The disease manifests in intestinal and urogenital forms.

Intestinal schistosomiasis usually results in diarrhoea and blood in the stool; 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. In men, urogenital schistosomiasis can induce disease in the seminal vesicles and prostate. The burden of schistosomiasis in 2016 was estimated at 2 543 364 disease-adjusted life years (DALYs).

Soil-transmitted helminthiases (STH) are caused by a group of intestinal parasites comprising Ascaris lumbricoides (roundworms), Trichuris trichiura (whipworms), Necator americanus and Ancylostoma duodenale (hookworms). STH are transmitted by faecal contamination of soil; they adversely affect nutritional status and impair cognitive processes. STH caused the loss of an estimated 3 452 655 DALYs in 2016; however, more than 500 000 DALYs/year have been estimated to have been averted by control.

WHO recommends preventive chemotherapy (PC) consisting of periodic administration of anthelmintic medicines (praziquantel for schistosomiasis and albendazole or mebendazole for STH) as a short-term measure for the control of morbidity associated with these infections.

In 2012, the World Health Assembly, in resolution 65.21, urged Member States to take advantage of other disease elimination activities to intensify schistosomiasis control programmes and initiate elimination campaigns where appropriate, through strengthened health systems, PC, provision of water and sanitation, hygiene education and snail control.

PC for schistosomiasis is required in 52 countries for a total of 219.9 million people: 120.3 million school-aged children (SAC) and 99.6 million adults. PC for STH is required in 101 countries. Since 2017, Burkina Faso and Mali are considered not to require PC for STH because of the long history of intervention and the very low STH prevalence. Globally, 272.7 million pre-SAC, 596 million SAC and 688 million women of reproductive age are estimated to require PC with albendazole or mebendazole. The goal of WHO is to treat at least 75% of SAC in all schistosomiasis-endemic countries and at least 75% of pre-SAC and SAC in all STH-endemic countries by 2020.

When schistosomiasis and STH are co-endemic, praziquantel and albendazole (or mebendazole) can be administered together safely.

This report documents progress in PC coverage for schistosomiasis and STH in 2017 at global and regional levels as reported by ministries of health. An online databank holds details on each endemic country, including data reported by nongovernmental organizations after validation of the information by countries. Details of the methods used to collect and analyse the data have been published.