Laboratórios de Parasitologia Molecular e de Biologia Parasitária, Instituto de Pesquisas Biomédicas e Faculdade de Biociências, PUCRS, Porto Alegre, Brazil.
PLoS Negl Trop Dis. 2007 Nov 14;1(2):e73. doi: 10.1371/journal.pntd.0000073.
Diagnosis of intestinal schistosomiasis in low endemic areas is a problem because often control measures have reduced egg burdens in feces to below the detection limits of classical coproparasitological methods. Evaluation of molecular methods is hindered by the absence of an established standard with maximum sensitivity and specificity. One strategy to optimize method performance, where eggs are rare events, is to examine large amounts of feces. A novel diagnostic method for isolation of Schistosoma mansoni eggs in feces, and an initial evaluation of its performance is reported here.
METHODOLOGY/PRINCIPAL FINDINGS: Known amounts of S. mansoni eggs were seeded into 30 g of normal human feces and subjected to a sequence of spontaneous sedimentation, sieving, Ritchie method, incubation and isolation through interaction with paramagnetic beads. Preliminary tests demonstrated the efficacy of lectins as ligands, but they also indicated that the paramagnetic beads alone were sufficient to isolate the eggs under a magnetic field through an unknown mechanism. Eggs were identified by microscopic inspection, with a sensitivity of 100% at 1.3 eggs per gram of feces (epg). Sensitivity gradually decreased to 25% at a concentration of 0.1 epg. In a preliminary application of the new method to the investigation of a recently established focus in southern Brazil, approximately 3 times more eggs were detected than with the thick-smear Kato-Katz method.
CONCLUSIONS/SIGNIFICANCE: The novel S. mansoni detection method may significantly improve diagnosis of infections with low burdens in areas of recent introduction of the parasite, areas under successful control of transmission, or in infected travelers. It may also improve the evaluation of new treatments and vaccines.
在低流行地区诊断肠血吸虫病是一个问题，因为通常的控制措施已经将粪便中的虫卵负担降低到经典粪便寄生虫检查方法的检测限以下。由于缺乏具有最大灵敏度和特异性的既定标准，因此对分子方法的评估受到阻碍。一种优化方法性能的策略是在很少出现虫卵的情况下检查大量粪便。本文报道了一种从粪便中分离曼氏血吸虫卵的新型诊断方法及其初步性能评估。
方法/主要发现：将已知数量的曼氏血吸虫卵播种到 30 克正常人粪便中，然后进行一系列自发沉淀、筛分、里奇法、孵育和通过与顺磁珠相互作用进行分离。初步试验证明了凝集素作为配体的有效性，但也表明单独的顺磁珠通过未知机制在磁场中足以分离卵。通过显微镜检查鉴定卵，在粪便中每克 1.3 个虫卵（epg）的浓度下灵敏度为 100%。灵敏度逐渐降低至 0.1 epg 时降至 25%。在对巴西南部最近建立的一个新疫区的初步应用中，该新方法检测到的卵数比厚涂片加藤法多约 3 倍。
结论/意义：新型曼氏血吸虫检测方法可能会显著改善对寄生虫新近传入地区、传播成功控制地区或感染旅行者的低负担感染的诊断。它还可能改善对新治疗方法和疫苗的评估。
