What does soil-transmitted helminth elimination look like? Results from a targeted molecular detection survey in Japan

The Deworm3 Project Team ,Mitsuko Hasegawa,Kristjana H Ásbjörnsdóttir,Arianna R Means,Steven A Williams,Hiroshi Ikuno,Judd L Walson,Shinjiro Hamano,Andrew M Gonzalez,Nils Pilotte,Toshihiko Sunahara,Jacqueline R M A Maasch,Marina Papaiakovou,Mihoko Kikuchi

doi:10.1186/s13071-019-3875-z

Abstract

BackgroundJapan is one of the few countries believed to have eliminated soil-transmitted helminths (STHs). In 1949, the national prevalence of Ascaris lumbricoides was 62.9%, which decreased to 0.6% in 1973 due to improvements in infrastructure, socioeconomic status, and the implementation of national STH control measures. The Parasitosis Prevention Law ended in 1994 and population-level screening ceased in Japan; therefore, current transmission status of STH in Japan is not well characterized. Sporadic cases of STH infections continue to be reported, raising the possibility of a larger-scale recrudescence of STH infections. Given that traditional microscopic detection methods are not sensitive to low-intensity STH infections, we conducted targeted prevalence surveys using sensitive PCR-based assays to evaluate the current STH-transmission status and to describe epidemiological characteristics of areas of Japan believed to have achieved historical elimination of STHs.MethodsStool samples were collected from 682 preschool- and school-aged children from six localities of Japan with previously high prevalence of STH. Caregivers of participants completed a questionnaire to ascertain access to water, sanitation and hygiene (WASH), and potential exposures to environmental contamination. For fecal testing, multi-parallel real-time PCR assays were used to detect infections of Ascaris lumbricoides, Necator americanus, Ancylostoma duodenale and Trichuris trichiura.ResultsAmong the 682 children, no positive samples were identified, and participants reported high standards of WASH.ConclusionsTo our knowledge, this is the first STH-surveillance study in Japan to use sensitive molecular techniques for STH detection. The results suggest that recrudescence of STH infections has not occurred, and that declines in prevalence have been sustained in the sampled areas. These findings suggest that reductions in prevalence below the elimination thresholds, suggestive of transmission interruption, are possible. Additionally, this study provides circumstantial evidence that multi-parallel real-time PCR methods are applicable for evaluating elimination status in areas where STH prevalence is extremely low.

Highlights

Japan is one of the few countries believed to have eliminated soil-transmitted helminths (STHs)
Among 682 individuals living in areas of Japan, previously endemic for STH infection, we did not detect any STH infection, suggesting that there is likely no STH recrudescence in the sampled areas
It appears that prior efforts to reduce STH transmission have likely resulted in sustained elimination of these infections

Summary

Introduction

Japan is one of the few countries believed to have eliminated soil-transmitted helminths (STHs). Current World Health Organization (WHO) guidelines for the management of STH infections focus on morbidity control through the use of mass drug administration (MDA) of anthelmintic drugs targeting preschool- and school-aged children as well as other at-risk groups [1]. This strategy can be successful in reducing the burden of high-intensity STH infections (those that result in morbidity) within a population, targeted MDA alone likely does not eliminate these infections, as reinfection remains common in treated communities.

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