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  • Title: Microscopic examination of Cryptosporidium oocysts in diarrhoeal stools.
    Author: Koonakosit R, Sriurairatna S, Petchclai B.
    Journal: J Med Assoc Thai; 1992 Jan; 75 Suppl 1():180-4. PubMed ID: 1402461.
    Abstract:
    Unconventional microscopic means for investigation of Cryptosporidium oocysts in patients' stools were explored in an attempt to obtain a more accurate diagnosis. The results showed that Nomarski interference contrast microscope provided clearer structures of oocysts in wet mount preparations than those under a normal light microscope and readily allowed distinction from yeast cells. Transmission electron microscopic study revealed that oocysts are thick walled and well sporulated. Their "untypical" appearance as seen by the light microscope resulted from sporozoites or the residuum that can be unfamiliar to some examiners. Electron microscopy provides definitive identification of Cryptosporidium spp. but Nomarski interference contrast microscopy was superior to bright field microscopy and may facilitate rapid diagnosis in routine fecal examination. The Ziehl-Neelsen modified acid fast technique was of value for differentiation and confirmation. Histological studies were conducted with fecal specimens of Cryptosporidium oocysts, organisms that often cause fatal watery diarrhea in AIDS patients, to better distinguish them from yeasts. The specimens were from 3 patients with AIDS or suspected AIDS. The method used were bright field and Nomarski interference contrast microscopy of wet-mounted stools preserved in 10% formalin and stained by Giemsa and by the Neelsen modified acid-fast technique. Electron microscope sections were postfixed in osmium tetroxide. Ultra-thin sections were stained with and lead citrate before microscopic examination. Oocysts appeared under bright field microscopy as 3x4 mcm ellipsoidal bodies with a central large round granule, known as the residuum, and 1-4 granules. Interference contrast microscopy revealed banana-shaped sporozoites surrounding the residuum, clearly differentiating them from yeasts. Giemsa stains the sporozoites pale blue with purple dots, making it difficult to distinguish them from yeasts. Acid-fast stain turned the crescent-shaped sporozoites red and the residuum deep red, while yeasts stained blue. Cryptosporidium could easily by distinguished from yeast ultrastructurally by their double cell wall. Thus, interference microscopy and acid-fast staining are helpful to separate Cryptosporidium from similar sized yeasts, an alternative to intestinal biopsy which has formerly been required to diagnose this parasite in immune-compromised patients.
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