Scoping review maps WASH evidence gaps in soil-transmitted helminth control

Soil-transmitted helminths (STH) are parasitic intestinal worms that infect humans through contact with, or ingestion of, soil contaminated with eggs shed by infected individuals. The group includes roundworms (Ascaris lumbricoides, Strongyloides stercoralis), whipworm (Trichuris trichiura) and hookworms (Ancylostoma duodenale, Necator americanus, Ancylostoma ceylanicum). Their transmission is shaped by water, sanitation and hygiene (WASH) services and practices.

A new scoping review, authored by Yael Velleman, Anne Straily, W. Evan Secor, Susana Vaz Nery and Laura Braun, set out to map how WASH-related risk factors relate to STH infection, and to assess whether the evidence aligns with plausible transmission pathways and conceptual frameworks.

Unlike past reviews, the authors deliberately did not assess effect sizes or the strength of associations. Instead, they characterised methodological features of the evidence base, including diagnostic approaches, that affect how comparable findings are across studies.

The review analysed 197 studies, of which 174 were observational and 23 were intervention studies. The authors found a substantial and growing body of evidence examining the relationship between WASH and other environmental exposures and the prevalence and intensity of STH infection.

Nonetheless, several important areas remain under-investigated. These include food chain pathways, environmental surveillance, under-studied STH species, and measures of service and infrastructure uptake and use, quality, and community coverage over time. According to the review, these gaps hamper drawing practical conclusions for improving service delivery.

The authors identify ways in which existing and new research can be enhanced. Routine investigations such as prevalence surveys should apply standard WASH definitions to reduce heterogeneity, and should apply a conceptual framework of transmission in study design.

Intervention studies, the review argues, should be based on theories of change that map actions disrupting transmission pathways, implementing a comprehensive intervention package and examining factors affecting behaviours or intervention compliance. Evaluation of intervention uptake should also be included in such studies.

New research should address the evidence gaps identified, and incorporate timelines with a realistic likelihood of impact into study planning and proposals. The authors note this is important given the environmental persistence of certain STH species and the fact that developing lasting and sustained behaviour change can be slow.

As a scoping review, the study maps the shape and methodological character of the existing evidence base rather than quantifying how strongly specific WASH measures reduce infection. Its contribution lies in identifying where evidence is missing, so that future observational studies and intervention trials can be designed to fill the gaps most relevant to controlling these parasitic worm infections.

Subject of Research: Evidence gaps in water, sanitation and hygiene research for soil-transmitted helminth control

Article Title: Water, sanitation, and hygiene in soil-transmitted helminth control: A scoping review of evidence gaps across transmission pathways

Article References: Velleman, Y., Straily, A., Secor, W. E., Vaz Nery, S., & Braun, L. (2026). Water, sanitation, and hygiene in soil-transmitted helminth control: A scoping review of evidence gaps across transmission pathways. PLOS Global Public Health, 6(10), e0006196. https://doi.org/10.1371/journal.pgph.0006196

Image Credits: AI Generated

DOI: 10.1371/journal.pgph.0006196

Keywords: soil-transmitted helminths, WASH, scoping review, sanitation, hygiene, transmission pathways, public health, neglected tropical diseases, prevalence surveys, intervention studies, Water, soil-transmitted