Laboratory Studies
Diagnosis is based on the microscopic detection of oocysts in fecal specimens. Stool testing for ova and parasites does not typically include testing for Cyclospora. Microscopic examination of fecal specimens with acid-fast staining are indicated in cyclosporiasis.
Oocysts of C cayetanensis stained with modified acid-fast stain. Note the variability of staining in the four oocysts. Courtesy of the CDC (http://phil.cdc.gov/phil/home.asp).
Stain Cyclospora species using modified Ziehl-Neelsen or Kinyoun acid-fast stains. These species are not visualized by Gram, Giemsa, silver, or hematoxylin-eosin staining.
Oocysts are round and resemble those of Cryptosporidium, but they are twice the size (8-10 µm). A modified safranin staining protocol provides consistent reddish-orange staining of oocysts and can simplify identification of the oocysts. [29]
Cyclospora spp oocysts are autofluorescent blue fluorescence is seen with UV light (330-365nm filter) and blue-green fluorescence can be seen with blue excitation (450-490nm filter). [30]
Oocyst of C cayetanensis viewed under UV microscopy. Courtesy of the CDC (http://phil.cdc.gov/phil/home.asp).
This property is not specific for Cyclospora species, however, and wanes as the specimen ages.
Examination of multiple stool samples, collected at different times is recommended as even symptomatic patients may not shed enough oocysts for detection.
No serologic assays are currently available to detect antibodies to Cyclospora species.
Polymerase chain reaction (PCR) tests for detection of Cyclospora DNA in stool specimens are available mainly for outbreak investigations; however, they are not currently approved by FDA. [30]
Procedures
Small-bowel biopsy reveals pathologic changes, however, they are non-specific. These include blunting and atrophy of villi with acute and chronic inflammation, and hyperplasia of crypts.
-
Life cycle of Cyclospora. (1) When freshly passed in stools, the oocyst is not infective; thus, direct fecal-oral transmission cannot occur and this differentiates Cyclospora from another important coccidian parasite, Cryptosporidium. (2) In the environment, sporulation occurs after days or weeks at temperatures between 22°C to 32°C, resulting in division of the sporont into two sporocysts, each containing two elongate sporozoites (3). Fresh produce and water can serve as vehicles for transmission (4) and the sporulated oocysts are then ingested in contaminated food or water (5). The oocysts exist in the gastrointestinal tract, freeing the sporozoites which invade the epithelial cells of the small intestine (6). Inside the cells, they undergo asexual multiplication and sexual development to mature into oocysts which will be shed in stools (7). The potential mechanisms of contamination of food and water are still under investigation. Courtesy of the CDC (http://phil.cdc.gov/phil/home.asp).
-
Oocysts of C cayetanensis stained with modified acid-fast stain. Note the variability of staining in the four oocysts. Courtesy of the CDC (http://phil.cdc.gov/phil/home.asp).
-
Oocyst of C cayetanensis viewed under UV microscopy. Courtesy of the CDC (http://phil.cdc.gov/phil/home.asp).
