Evaluation of Commercially Available Preservatives for Laboratory Detection of Helminths and Protozoa in Human Fecal Specimens

Formalin and mercuric chloride-based low-viscosity polyvinyl alcohol (LV-PVA) are widely used by most diagnostic parasitology laboratories for preservation of helminth eggs and protozoan cysts and trophozoites in fecal specimens. Concerns about the toxicity of formalin and the difficulty of disposal of LV-PVA are powerful incentives to use alternate preservatives. Such alternatives have been marketed by several companies and are often presented as one-vial, non-mercuric chloride fixatives that aim at performing the same role as formalin and PVA combined. We compared five, one-vial commercial preservatives, two from Meridian Diagnostics, Inc. (Ecofix and sodium acetate-acetic acid-formalin), and one each from Scientific Device Laboratories, Inc. (Parasafe), Alpha Tec Systems, Inc. (Proto-fix), and Streck Laboratories, Inc. (STF), with 10% formalin and LV-PVA. Fecal specimens obtained from patients in a Brazilian hospital were aliquoted within 12 h of collection into the seven preservatives mentioned above and were processed after 1 month at the Centers for Disease Control and Prevention. Direct and concentrated permanent smears as well as concentrates for 20 positive specimens (a total of 259 processed samples) were prepared, stained according to the manufacturers' instructions, examined, and graded. Positive specimens contained one or more parasites with stages consisting of eggs, larvae, cysts, and a few trophozoites of Giardia intestinalis. Criteria for assessment of the preservatives included the quality of the diagnostic characteristics of helminth eggs, protozoan cysts, and trophozoites, ease of use, and cost. Acceptable alternatives to formalin for wet preparations were found. Ecofix was found to be comparable to the traditional “gold standard” LV-PVA for the visualization of protozoa in permanent stained smears. This study suggests that more acceptable alternatives to the traditional formalin and LV-PVA exist.

以福尔马林（Formalin）和氯化汞为基础的低黏度聚乙烯醇（low-viscosity polyvinyl alcohol, LV-PVA），被绝大多数诊断寄生虫学实验室广泛应用于粪便标本中蠕虫卵、原虫包囊及滋养体的保存。由于福尔马林具有毒性，且低黏度聚乙烯醇（LV-PVA）存在处置困难的问题，开发替代保存液成为重要的研究动力。目前已有多家企业推出此类替代产品，这类产品多以单瓶、无氯化汞固定液的形式上市，旨在实现福尔马林与LV-PVA联合使用的同等效果。本研究对5种商用单瓶保存液与10%福尔马林及LV-PVA进行了对比评估，其中2种来自Meridian Diagnostics, Inc.（Ecofix与乙酸-乙酸钠-福尔马林保存液），其余3种分别来自Scientific Device Laboratories, Inc.（Parasafe）、Alpha Tec Systems, Inc.（Proto-fix）及Streck Laboratories, Inc.（STF）。研究样本取自巴西某医院的患者粪便标本，在标本采集12小时内将其分装至上述7种保存液中，于1个月后送至美国疾病控制与预防中心（Centers for Disease Control and Prevention）进行处理。针对20份阳性标本（共计259份处理样本），研究者制备了直接涂片、浓缩永久涂片及浓缩湿片，按照各生产商的操作说明完成染色后开展镜检与分级评估。阳性标本包含至少一种寄生虫的不同发育阶段，包括虫卵、幼虫、包囊以及少量蓝氏贾第鞭毛虫（Giardia intestinalis）滋养体。本次评估的指标包括蠕虫卵、原虫包囊及滋养体的诊断特征质量、操作便捷性与检测成本。研究发现，用于湿片检测的福尔马林替代保存液已具备可接受的应用性能；其中Ecofix在永久染色涂片中原虫的可视化效果可媲美传统"金标准"LV-PVA。本研究表明，现有替代传统福尔马林与LV-PVA的保存液已拥有更优的应用价值。