Identification of intracellular stages of Cyclospora species by light microscopy of thick sections using hematoxylin

Cyclospora sp is a recently identified coccidia responsible for enteric infection in humans. Most reports have failed to detect this parasite in intestinal biopsies by light microscopy, although the different stages have been ultrastructurally described in jejunum enterocytes. Very recently, some investigators have reported the detection by light microscopy of parasitophorous vacuoles in intestinal biopsies; however, only transmission electron microscopy (TEM) could clearly identify the parasitic stages. To improve the histological diagnosis without using TEM, we have tested different staining methods in biopsies obtained from a patient infected by the human immunodeficiency virus who was shedding Cyclospora oocysts. Hematoxylin stain alone for 15 minutes on 5 μm-thick sections of duodenal biopsies was found to be the most efficient method for observing different stages of the parasite. In particular, the banana-shaped merozoites were visualized and appeared very similar to the human coccidia Isopora belli. This simple technique may be useful in diagnosing Cyclospora infection.