Diagnosis of Cyclosporiasis

Ultraviolet fluorescence microscopy is one method of examining stool specimens for Cyclospora oocysts. The oocyst wall is autofluorescent. (Credit: CDC DPDx)

Health care providers should consider Cyclospora as a potential cause of prolonged diarrheal illness, particularly in patients with a history of recent travel to Cyclospora-endemic areas. Testing for Cyclospora is not routinely done in most U.S. laboratories, even when stool is tested for parasites. Therefore, if indicated, health care providers should specifically request testing for Cyclospora.

Cyclospora infection is diagnosed by examining stool specimens. Diagnosis can be difficult in part because even persons who are symptomatic might not shed enough oocysts in their stool to be readily detectable by laboratory examinations. Therefore, patients might need to provide several specimens collected on different days. In addition, the laboratory should use sensitive recovery methods (concentration procedures) and detection methods that highlight Cyclospora oocysts. The oocysts can be stained with modified acid-fast or modified ("hot") safranin techniques. Cyclospora oocysts also are autofluorescent, meaning that when stool containing the parasite is viewed under an ultraviolet (UV) fluorescence microscope the oocysts appear blue or green (see image above) against a black background. Molecular diagnostic methods, such as polymerase chain reaction (PCR) analysis, are used to look for the parasite's DNA in the stool.

Additional perspective about laboratory testing for Cyclospora

• Cyclospora oocysts are easily overlooked; low-level shedding (~1-2 logs lower than for Cryptosporidium species) is common. To maximize recovery of Cyclospora oocysts, first concentrate the stool specimen—such as by the formalin-ethyl acetate technique (centrifuge for 10 minutes at 500 x g)—and then examine a wet mount and/or a stained slide of the sediment.
• Cyclospora oocysts are ~8-10 micrometers in diameter (in contrast, Cryptosporidium parvum/hominis oocysts are ~4-6 micrometers in diameter).
• Ultraviolet fluorescence microscopy (UV excitation filter set at 330-365 nm or 450-490 nm) is a sensitive technique for rapidly examining stool sediments for Cyclospora oocysts, which stand out because they autofluoresce (Cryptosporidium parvum/hominis oocysts do not). If suspect Cyclospora oocysts are found, bright-field, phase contrast, or differential interference contrast microscopy can then be used to confirm that the structures have the characteristic morphologic features of Cyclospora oocysts (i.e., are nonrefractile spheres that contain undifferentiated cytoplasm or refractile globules).
• On a modified acid-fast—stained slide of stool, Cyclospora oocysts typically are variably acid fast (i.e., in the same field, oocysts may be unstained or stain from light pink to deep red). Unstained oocysts characteristically have a wrinkled (hyaline) appearance.
• If a "hot" modified safranin technique is used, Cyclospora oocysts uniformly stain a brilliant reddish orange.

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