Evaluation of Traditional and Contemporary Methods for Detecting Syphacia obvelata and Aspiculuris tetraptera in Laboratory Mice

Abstract

There is no consensus regarding the best practice for detecting murine pinworm infections. Initially, we evaluated 7 fecal concentration methods by using feces containing Aspiculuris tetraptera (AT) eggs (n = 20 samples per method). Sodium nitrate flotation, sodium nitrate centrifugation, Sheather sugar centrifugation, and zinc sulfate centrifugation detected eggs in 100% of samples; zinc sulfate flotation and water sedimentation detected eggs in 90%. All had better detection rates than Sheather sugar flotation (50%). To determine optimal detection methods, Swiss Webster mice were exposed to Syphacia obvelata (SO; n = 60) or AT (n = 60). We compared the following methods at days 0, 30, and 90, beginning 21 or 28 d after SO and AT exposure, respectively: fecal concentration (AT only), anal tape test (SO only), direct examination of intestinal contents (cecum and colon), Swiss roll histology (cecum and colon), and PCR analysis (pooled fur swab and feces). Detection rates for SO-exposed mice were: PCR analysis, 45%; Swiss roll histology, 30%; intestinal content exam, 27%; and tape test, 27%. The SO detection rate for PCR analysis was significantly greater than that for the tape test. Detection rates for AT-exposed mice were: intestinal content exam, 53%; PCR analysis, 33%; fecal flotation, 22%; and Swiss roll histology, 17%. The AT detection rate of PCR analysis combined with intestinal content examination was greater than for PCR analysis only and the AT detection rate of intestinal content examination was greater than for Swiss roll histology. Combining PCR analysis with intestinal content examination detected 100% of infected animals. No single test detected all positive animals. We recommend combining PCR analysis with intestinal content examination for optimal pinworm detection.

Figure 1.

Swiss roll histology. (A) Subgross photomicrograph demonstrating a Swiss roll. (B) Transverse and oblique sections of a gravid female S. obvelata (arrows) within the lumen of the cecum. The bar = 200 µm. (C) Gravid female S. obvelata with characteristic platymyarian musculature (asterisk), gastrointestinal tract lined by uninucleate cuboidal epithelial cells (arrowhead), and thick-shelled, asymmetrically ellipsoidal eggs measuring approximately 30 × 80 μm (arrows). Hematoxylin and eosin stain. The bar = 200 µm.

Figure 2.

Detection rates (percentage positive) for S. obvelata-exposed mice, comparing the tape test (20 mice per time point; n = 60 total), examination of intestinal contents (10 mice per time point; n = 30 total), Swiss roll histology (10 mice per time point; n = 30 total), and PCR analysis (20 per time point; n = 60 total) on days 0, 30, 90, and for all time points combined. The ‘total positive’ data represent the number of mice positive by at least one test method (20 mice per time point; n = 60 total). The number within the bar represents the number of positive mice. ‡, P = 0.001 (McNemar test) for PCR analysis compared with the tape test for all time points combined.

Figure 3.

Detection rates (percentage positive) for A. tetraptera-exposed mice, comparing fecal flotation (20 mice per time point; n = 60 total), examination of intestinal contents (10 mice per time point; n = 30 total), Swiss roll histology (10 mice per time point; n = 30 total), and PCR analysis (20 mice per time point; n = 60 total) on days 0, 30, 90, and for all time points combined. The ‘total positive’ data represent the number of mice positive by at least one test method (20 mice per time point; n = 60 total). The number within the bar represents the number of positive mice. Detection rate differed significantly between examination of intestinal contents compared with Swiss roll histology on day 90 (‡, P = 0.001, Fisher exact test) and for all time points combined (†, P = 0.01, Fisher exact test); a, P = 0.002 (McNemar test) for PCR analysis combined with examination of intestinal contents compared with PCR analysis only for all time points combined; b, P = 0.02 (McNemar test) for PCR analysis combined with fecal flotation compared with Swiss roll histology for all time points combined; c, P = 0.004 (McNemar test) for PCR analysis combined with examination of intestinal contents compared with PCR analysis combined with fecal flotation for all time points combined.