Elimination on the Horizon: Prevalence of Schistosomiasis, a Neglected Tropical Disease, Decreases by Nearly 60%

03.12.2021

In a new study by the Swiss Tropical and Public Health Institute (Swiss TPH), researchers found that the prevalence of schistosomiasis among school-aged children decreased by nearly 60% between 2000 and 2019 due to large-scale drug administration and social and economic development of the African continent. The findings offer hope of elimination for this major neglected tropical disease. The study was published yesterday in the Lancet Infectious Diseases.

If policy makers, the WHO and national programmes further amplify their efforts for disease control, it is feasible to eliminate schistosomiasis as a public health problem. Photo credit: Thomas Schuppisser.

Schistosomiasis is a parasitic worm infection that continues to be a major public health problem, particularly in sub-Saharan Africa. Over the past 20 years, control efforts against this neglected tropical disease (NTD) have scaled up, with mass drug administration with the drug praziquantel serving as the main intervention.

In a new study led by the Swiss Tropical and Public Health Institute (Swiss TPH), researchers assessed the effect of mass drug administration on the distribution of schistosomiasis over time and found that the prevalence of schistosomiasis in sub-Saharan Africa reduced by 58.3% in school-aged children between 2000 and 2019. The study was published yesterday in the Lancet Infectious Diseases.

“The decrease in schistosomiasis prevalence is related to the scaling up of mass drug administration over the past 15 years, as well as factors such as economic and social development on the African continent, including greater access to clean water and sanitation,” said Penelope Vounatsou, Head of Biostatistics Unit at Swiss TPH. “These findings are encouraging that we are on the right track to eliminating this NTD as a public health problem.”

Novel findings using mathematical modelling

The study analyzed cross-sectional survey data of school-aged children (aged 5-14 years) in 44 countries of sub-Saharan Africa. Bayesian geostatistical models were used with both the Schistosoma haematobium and S. mansoni data at three different time periods (2000-2010, 2011-2014, and 2015-2019) using data extracted from the Global Neglected Tropical Diseases (GNTD) database and recent national survey data provided by disease control programmes and the World Health Organization (WHO).

“Our model-based predictions confirm that schistosomiasis has decreased significantly and that several countries may already be in a position to start considering elimination strategies,” said Vounatsou. “This promising outcome indicates that it is feasible to eliminate schistosomiasis as a public health problem, so long as policy makers, the WHO and national programmes further amplify their disease control efforts.”

In addition to analyzing the prevalence, researchers also updated the estimates of the number of infected school-aged children and treatment needs in sub-Saharan African for schistosomiasis in order to align them with the WHO roadmap.

“The research will assist policy makers to plan their future schistosomiasis control strategies according to the prevalence trends from the past several years,” said Vounatsou. “We are proud to provide a measure of programme assessment and evaluation by using prevalence estimated before, during and after major scale-up of mass drug administration, as well as evidence on the effect of future socioeconomic and environmental factors that should be considered for control projects.”

Continued partnership needed

Over the past 14 years, praziquantel has been made available by Merck in increasing amounts. Each year, in partnership with the WHO and ministries of health, up to 250 million tablets are provided free of charge. “It has been excellent to see contributions from donors, implementation partners and Merck for the medicine, yet continued support and targeted interventions are needed to sustain the trend and eliminate the disease as a public health problem as set by the new NTD road map 2021-2030,” said Amadou Garba Djirmay, scientist at the WHO. “Praziquantel has been targeted at school-aged children, and limited access to the drug for at-risk adult populations and preschool-aged children remains a key issue in further scaling up control efforts.”

“The global NTD community has achieved remarkable progress in the fight against schistosomiasis and other infectious diseases of poverty,” said Jürg Utzinger, Director of Swiss TPH. “Strong partnership, large-scale deworming, continued social and economic development, education and communication strategies and better access to water, sanitation and hygiene will facilitate the further decrease of schistosomiasis and allow us to work towards the ultimate goal of disease elimination.”

WHO Collaborating Centre for Epidemiology and Control of Helminth Infections

In 2014, Swiss TPH became a WHO Collaborating Centre for Epidemiology and Control of Helminth Infections. The work is comprised of teaching and training, risk area mapping, evaluating existing and developing new diagnostic tools, screening of new substances for their efficacy and safety against parasitic worms and supporting countries in building their control programmes.

Pediatric Praziquantel Consortium

The Pediatric Praziquantel Consortium is an international public-private partnership led by Merck that is dedicated to the development of a pediatric medication to treat schistosomiasis in preschool-aged children. Swiss TPH contributes to the consortium with extensive experience in helminth biological and pharmacological research, epidemiology, clinic research in endemic regions and access to the new medication.

About the study

The study was conducted by the Swiss Tropical and Public Health Institute (Swiss TPH) in collaboration with the World Health Organization (WHO), the University of Basel, a number of national control programmes for NTDs in Africa and other partners. The research was funded by the European Research Council (ERC) and the World Health Organization (WHO).  

Kokaliaris, C. et al. (2021). Effect of preventive chemotherapy with praziquantel on schistosomiasis among school-aged children in sub-Saharan Africa: a spatiotemporal modelling study. Lancet Infectious Diseases.

Subscribe to our newsletter and get all the latest research news, project updates, course and event listings from Swiss TPH.