About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

CPT Codes

Quizzes, General

Quizzes, Histology

Quizzes, Blood

Review Tests


Information Tables

Organism Index (A-Z)

New Infections

Introduction | Cyclospora cayetanensis | Microsporidia

Cyclospora Cayetanensis


Cyclospora cayetanensis is a newly identified organism that was originally mistaken for other pathogens, including cyanobacteria and other coccidia. When the first oocysts were seen, they were not mature and were not recognized as true coccidia. The mature oocyst contains two sporocysts, each containing two sporozoites, a pattern which places these organisms in the coccodian genus Cyclospora. The name Cyclospora cayetanensis has been proposed; the species name comes from the university in Peru where it was initially studied (Universidad Peruana Cayetano Heredia). Infection with this coccidian parasite has been linked to the importation of fresh produce into the United States (raspberries from Guatemala, fresh basil, fresh baby lettuce leaves).

Unsporulated oocysts are passed in the stool, and sporulation occurs within about 5 to 13 days. Currently, the life cycle has not been totally defined and there is very little definitive information related to potential reservoir hosts. Individuals of all ages can become infected, immunocompetent, as well as immunocompromised persons. In several geographic areas throughout the world, there appears to be some seasonal variation liked to increased rainfall and spring and summer weather. However, in other areas, there may be no specific seasonality.

Clinical Presentation

There is generally 1 day of malaise and low-grade fever, with rapid onset of diarrhea. There may be fatigue, anorexia, vomiting, myalgia, and weight loss. The diarrhea may be self-limiting after 3 to 4 days, but is characterized by relapses lasting for from 4 to 7 weeks. In patients with AIDS, symptoms may last for several months; biliary disease has also been reported in this group.


Currently, trimethroprim-sulfamethoxazole (TMP-SMX) is the drug of choice; relief of symptoms has been seen in 1 to 3 days posttreatment. However, recurrence of symptoms occurs within 1 to 3 months in over 40% of patients.


The coccidian oocysts stain orange with safranin and are acid-fast variable; some organisms will stain deep red/purple with a mottled appearance but no internal structures. Clean, wet mounts show nonrefractile objects that appear as glassy, wrinkled spheres. Using modified acid-fast stains, they may stain from purple to pale (essentially no color). It is important to remember that the stain decolorizer should be no stronger than a 1% sulfuric acid. When modified acid-fast stains were first used to stain Cryptosporidium parvum, the decolorizer was a 3% to 5% sulfuric acid; this is too strong for Cyclospora - too much color is removed. The 1% acid formula works well for C. parvum, C. cayetanensis, and Isospora belli. The oocysts often have a wrinkled appearance (like wrinkled cellophane). The oocysts autofluoresce strong green or blue, depending on the filters used (Green: 450-490 DM excitation filter; Blue: 365 DM excitation filter) under UV epifluorescence. During concentration of stool specimens, centrifugation speed and time should be 500xg for 10 min.


Little information is available regarding reservoir animal hosts and environmental survival time; however, the oocysts tend to be resistant to adverse conditions and can survive for long periods of time if kept moist. There is every reason to believe that the oocysts can be transmitted through contaminated food and/or water, similar to that seen with Cryptosporidium parvum.

Stained Slides

This photograph shows a single Cyclospora cayetanensis oocyst; they measure about 8 to 10 microns. The stain is a modified acid-fast stain and the decolorizer was a 1% sulfuric acid.

This photograph shows many Cyclospora cayetanensis oocysts; the stain is a modified acid-fast stain. Note the tremendous color variation; remember that this organism is acid-fast variable, even when using a gentle decolorizer (do not use acid-alcohol). Some of the oocysts will appear somewhat "wrinkled"- these oocysts have been been described as looking like "wrinkled cellophane."

This photograph shows two "ghost cells" - Cyclospora cayetanensis as they might appear on a Wheatley's Trichrome stain. Unless there are numerous oocysts present in the specimen, these may be missed.

This photograph shows the autofluorescence seen using the same filters as for Calcofluor white fluorescence. A small portion of the specimen is added to some saline and then examined under the fluorescent microscope - no dyes are used in the process, just specimen, saline, and then examination. Note the small blue rings, these are the oocysts.