Microscopic examination of Cryptosporidium oocysts in diarrhoeal stools

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.