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

Abstract

Background: Japan 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.Methods: Stool 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.Results: Among the 682 children, no positive samples were identified, and participants reported high standards of WASH. Conclusions:To 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.

Towards soil-transmitted helminths transmission interruption: The impact of diagnostic tools on infection prediction in a low intensity setting in Southern Mozambique

“…qPCR demands a high-tech lab equipment and high cost consumables [ 50 ] but it is very sensitive using a single stool [ 45 ]. qPCR could ascertain sustained or increased transmission once MDA is halted [ 37 , 38 , 49 ]; it was used to confirm transmission interruption in Japan [ 5 ]. In addition, qPCR could integrate other helminths surveillance, such as schistosomiasis or strongyloidiasis [ 51 ].…”

“…To decrease transmission and reinfection, WHO also recommends interventions intended to increase the accessibility to safe water, improved sanitation, and hygiene (WASH) [3]. Some regions are approaching WHO goal of reducing the proportion of moderate and high intensity infections to less than 2% and, thus, reaching STH elimination as a public health problem [4,5]. But transmission could rebound from residual hotspots if interventions are halted without a thorough epidemiological evaluation [6].…”

“…Some regions are approaching WHO goal of reducing the proportion of moderate and high intensity infections to less than 2% and, thus, reaching STH elimination as a public health problem [ 4 , 5 ]. But transmission could rebound from residual hotspots if interventions are halted without a thorough epidemiological evaluation [ 6 ].…”

Natural Wastewater Treatment Systems for Prevention and Control of Soil-Transmitted Helminths

“…These helminths are distributed throughout the world. Globally, about two billion people are infected with at least one species of STHs with those having heavy infections presenting considerable morbidities including malnutrition, allergy, and respiratory difficulties including asthma and Löffler's syndrome, diarrhea, intestinal obstruction, rectal prolapse, anemia, and cognitive development problems [19]. With limited access to clean and safe water often leading to poor hygiene and insufficient sanitation services, frequency of helminthiasis is higher in low-and middle-income countries than in high-income countries [15].…”

<i>Trichuris trichiura</i> Incidentally Detected by Colonoscopy and Identified by a Genetic Analysis

“…In 2017, the World Health Organization reported that approximately 460 million people worldwide were infected with Trichuris trichiura ( 1 ). However, the incidence of trichuriasis in Japan has decreased in recent years due to improvements in environmental hygiene ( 2 ).…”