I acknowledge, with gratitude, much help received from Dr.
Youssef, Senior Veterinary Anatomic Pathologist, IDEXX Reference Laboratory-University of Guelph, Ontario Canada for his interest and reading the draft of this paper and for his constructive comments. MCR methodology was developed and validated in four steps: (1) preparation of images for measurement (image digitalization), (2) design of a movable computer ruler (MCR), (3) use of MCR to measure sizes of parasites, and (4) validation of the measurements by comparison with traditional Acknowledgments S2 shows, using a 100× objective lens (Tz100×), the sd = 1 μm, the length is 7.5 sd (equals 7.5 μm), and width is DiscussionĪ new method to measure the size of selected parasites was developed using a movable computer ruler (MCR ) using images obtained by either a digital or non-digital (35 mm) camera attached to a light microscope. Measuring the size of Toxoplasma tachyzoites (Tz)Īs Fig. Measuring different sizes of Toxoplasma cysts, with same lens powerĭifferent sizes of ten Tc measured in the same brain scrape (Fig. However, the diameter measured using 100× (32.5 μm) was the most accurate as shown in Table 1.
The diameter of the same Tc depended on the objective lens used (Fig. Additionally, eggs of the nematode Trichostrongylus sp., the cestode Moniezia expansa, and the oocyst of Eimeria bateri were obtained from fecal smears of their corresponding host (see Measuring the diameter of Toxoplasma cysts (Tc) acquired by different lens powers Toxoplasma gondii cysts in a fixed scrape from a mouse brain 30 days post infection, and Toxoplasma tachyzoites in fresh smears from peritoneal fluid of a mouse 7 days post infection were mainly used. Images of selected parasites were chosen for measurement and to demonstrate the use of this new method. Here, a new computerized method for measuring parasites or other objects is described which depends on digital images of both the parasite and stage micrometer. In another approach, a stage micrometer can be used on its own, measuring printed images of both the parasite under the study and the stage micrometer acquired by the same objective lens (Chantangsi, 2002).įinally, some of the newer digital cameras attached to microscopes are provided with distance measurement software, which can be used, after calibration, for measurement of parasites. A combination of these methods is used to calibrate the ocular scale unit with different objective lenses to determine the calibration factor for each lens. The most widely used techniques for measuring parasites by light microscopy are the ocular micrometer disk, screw micrometer eyepiece, and stage micrometer.
Several methods have been described that differ in their application and accuracy, and many of them require time, effort and experience (Gonzalez-Ruiz and Bendall, 1995, Cavanihac, 2000, Dioni, 2002 Zajac and Conboy, 2006). Measuring the diagnostic stages of morphologically indistinguishable parasites or non-fixed living parasites such as nematode larvae, trypanosomes and ciliates on fresh smears can be difficult.
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