Hookworm and Strongyloides stercoralis infections in school-age children and cohabiting dogs in Cambodia following 5 years of bi-annual mass drug administration: a cross-sectional observational study.
TL;DR
The higher S stercoralis haplotype diversity in children compared with dogs suggests that S stercoralis transmission in the human population is complex, likely involving a potentially prevalent human-to-human transmission.
Abstract
Background
Despite sustained control efforts, soil-transmitted helminths remain a major public health burden in endemic regions, with companion animals, particularly dogs, acting as potential reservoirs further complicating elimination efforts. In this study we aimed to assess infection levels in school-age children following 5 years of bi-annual school-based deworming and to investigate the contribution of dogs to ongoing zoonotic transmission in rural Cambodia.
Methods
A cross-sectional observational study was conducted across 14 villages and five primary schools in Ta Ches commune, Kampong Chhnang province, Cambodia. These primary schools were receiving bi-annual preventive chemotherapy and villages within the commune were chosen based on the residential locations of the children attending these schools. All children aged 6-15 years enrolled in grades 1-6 attending the five participating schools and dog owners residing in the 14 villages were invited to participate. No random sampling or stratification was applied. Human and dog faecal samples were collected and screened using quantitative PCR. Samples from either children or dogs containing insufficient faecal material for DNA extraction were excluded. DNA sequencing and robust statistical approaches were performed to investigate zoonotic transmission dynamics between children and cohabiting dogs. The primary outcome of this study was the level of soil-transmitted helminth infections.
Findings
Between Dec 2, and Dec 15, 2019, 706 children and 474 cohabiting dogs were included in the study. Soil-transmitted helminths were detected in 320 (45% [95% CI 42-49]) of 706 children, with hookworm infections predominating (302 [43%; 40-47]). Moderate-heavy infections exceeded the 2% WHO threshold needed for elimination. In 10 (71%; 50-93) of 14 villages, children and dogs harboured Ancylostoma ceylanicum, Strongyloides stercoralis, or a combination of the two, with combined zoonotic infections in 47 (15%; 11-19) children. We found that A ceylanicum and S stercoralis sequences from dogs and children clustered together with no clear distinction. However, the higher S stercoralis haplotype diversity in children compared with dogs suggests that S stercoralis transmission in our human population is complex, likely involving a potentially prevalent human-to-human transmission.
Interpretation
Despite 5 years of targeted bi-annual mass drug administration, hookworms and S stercoralis remain a major public health issue in Cambodia. Our findings highlight the limitations of school-based deworming strategies and underscore the need for integrated molecular surveillance and One Health interventions to achieve the 2030 soil-transmitted helminths elimination targets.
Funding
The University of Melbourne McKenzie Fellowship and the Soulsby Foundation.