Steinbaum Lauren, Kwong Laura H, Ercumen Ayse, Negash Makeda S, Lovely Amira J, Njenga Sammy M, Boehm Alexandria B, Pickering Amy J, Nelson Kara L
Civil and Environmental Engineering, Stanford University, Stanford, California, United States of America.
School of Public Health, University of California, Berkeley, Berkeley, California, United States of America.
PLoS Negl Trop Dis. 2017 Apr 5;11(4):e0005522. doi: 10.1371/journal.pntd.0005522. eCollection 2017 Apr.
Globally, about 1.5 billion people are infected with at least one species of soil-transmitted helminth (STH). Soil is a critical environmental reservoir of STH, yet there is no standard method for detecting STH eggs in soil. We developed a field method for enumerating STH eggs in soil and tested the method in Bangladesh and Kenya. The US Environmental Protection Agency (EPA) method for enumerating Ascaris eggs in biosolids was modified through a series of recovery efficiency experiments; we seeded soil samples with a known number of Ascaris suum eggs and assessed the effect of protocol modifications on egg recovery. We found the use of 1% 7X as a surfactant compared to 0.1% Tween 80 significantly improved recovery efficiency (two-sided t-test, t = 5.03, p = 0.007) while other protocol modifications-including different agitation and flotation methods-did not have a significant impact. Soil texture affected the egg recovery efficiency; sandy samples resulted in higher recovery compared to loamy samples processed using the same method (two-sided t-test, t = 2.56, p = 0.083). We documented a recovery efficiency of 73% for the final improved method using loamy soil in the lab. To field test the improved method, we processed soil samples from 100 households in Bangladesh and 100 households in Kenya from June to November 2015. The prevalence of any STH (Ascaris, Trichuris or hookworm) egg in soil was 78% in Bangladesh and 37% in Kenya. The median concentration of STH eggs in soil in positive samples was 0.59 eggs/g dry soil in Bangladesh and 0.15 eggs/g dry soil in Kenya. The prevalence of STH eggs in soil was significantly higher in Bangladesh than Kenya (chi-square, χ2 = 34.39, p < 0.001) as was the concentration (Mann-Whitney, z = 7.10, p < 0.001). This new method allows for detecting STH eggs in soil in low-resource settings and could be used for standardizing soil STH detection globally.
全球约有15亿人感染了至少一种土源性蠕虫（STH）。土壤是STH的重要环境储存库，但目前尚无检测土壤中STH虫卵的标准方法。我们开发了一种在土壤中计数STH虫卵的现场方法，并在孟加拉国和肯尼亚对该方法进行了测试。通过一系列回收率实验对美国环境保护局（EPA）在生物固体中计数蛔虫卵的方法进行了改进；我们在土壤样本中接种已知数量的猪蛔虫卵，并评估方案修改对虫卵回收率的影响。我们发现，与0.1%吐温80相比，使用1% 7X作为表面活性剂可显著提高回收率（双侧t检验，t = 5.03，p = 0.007），而其他方案修改（包括不同的搅拌和浮选方法）则没有显著影响。土壤质地影响虫卵回收率；与使用相同方法处理的壤土样本相比，沙质样本的回收率更高（双侧t检验，t = 2.56，p = 0.083）。我们记录了实验室中使用壤土的最终改进方法的回收率为73%。为了对改进后的方法进行现场测试，我们在2015年6月至11月期间处理了来自孟加拉国100户家庭和肯尼亚100户家庭的土壤样本。土壤中任何STH（蛔虫、鞭虫或钩虫）虫卵的检出率在孟加拉国为78%，在肯尼亚为37%。孟加拉国阳性样本中土壤STH虫卵的中位数浓度为0.59个虫卵/克干土，肯尼亚为0.15个虫卵/克干土。孟加拉国土壤中STH虫卵的检出率和浓度均显著高于肯尼亚（卡方检验，χ2 = 34.39，p < 0.001；曼-惠特尼检验，z = 7.10，p < 0.001）。这种新方法能够在资源匮乏地区检测土壤中的STH虫卵，可用于全球土壤STH检测的标准化。
