Cyclosporiasis laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]
Overview
Laboratory Findings
- Cyclospora infection is diagnosed by examining stool specimens.
- Laboratory 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.
- Laboratory diagnosis can be difficult as the cyclospora oocysts may not be detected in stool, even if the patient is symptomatic.
- Therefore, patients might need to submit several specimens collected on different days.
- Special techniques, such as acid-fast staining, are often used to make Cyclospora oocysts more visible under the microscope.
- In addition, Cyclospora oocysts are autofluorescent, meaning that when stool containing the parasite is viewed under an ultraviolet (UV) fluorescence microscope the parasite appears blue or green 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.[1]
Stool Examination
Wet Mount
- In bright-field microscopy using differential interference contrast (DIC), oocysts appear as refractile spheres (8 to 10 μm) with a distinct oocyst wall, but may be confused with other objects. Under UV fluorescence microscopy, the oocyst wall autofluoresces.
- An intense blue fluorescence is obtained with the preferred UV excitation filter set (330 to 365 nm).
- If this filter set is not available, a less intense green fluorescence can be obtained with blue excitation (450 to 490 nm).
- A fluorescence microscope is required and this procedure does not provide a stained slide that can be archived.
- Both DIC and UV fluorescence microscopy are efficient and reliable approaches for identification of cyclospora.
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Modified Acid Fast Stain
A blue-green background, or contrasting counterstain, of fecal debris allows the oocysts to stand out. The oocysts are variably stained: some will stain light pink to deep purple, while others may be unstained. The oocysts (8 to 10 μm) may not be perfectly round; some may appear collapsed or distorted on one side. They may contain granules and/or have a wrinkled oocyst wall appearance (characteristics that distinguish oocysts from acid-fast artifacts). This staining method is the easiest and most practical, and provides a stained slide that can be archived. Misdiagnosis can result, however, due to the variability in staining and confusion with artifacts.
Shown below are images of oocysts of cyclospora stained with modified acid fast stain.
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Safranin Stain
Oocysts stain uniformly, red to reddish-orange. This uniform staining decreases the risk of misdiagnosis. However, this technique requires heating, therefore additional equipment is necessary (e.g., microwave oven).
Shown below are images of oocysts of cyclospora stained with safranin stain.
Trichrome Stain
Oocysts may be detected, but should not be confirmed, by this method. Because trichrome stain is the routine staining technique for stool specimens in most laboratories, laboratorians should be familiar with the appearance of Cyclospora stained with trichrome in order to detect oocysts during routine ex-aminations. However, this staining method is inadequate for definitive diagnosis because all oocysts will appear unstained. Oocysts appear as clear, round, and somewhat wrinkled spheres (8 to 10 μm). The diagnostic techniques listed above should be used to confirm Cyclospora when the presence of this coccidian is suspected in a trichrome stained smear.[3]
Polymerase Chain Reaction
Molecular diagnostic methods, such as polymerase chain reaction (PCR) analysis, are used to look for the parasite's DNA in the stool.[4]