Cyclospora cayetanensis, a coccidian protozoan. It appears that all human cases are caused by this species.
- Herwaldt BL. Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s. Clin Infect Dis 2000;31:1040-1057.
- Ortega YR, Gilman RH, Sterling CR. A new coccidian parasite (Apicomplexa: Eimeriidae) from humans. J Parasitol 1994;80:625-629.
- Pieniazek NJ, Herwaldt BL. Reevaluating the molecular taxonomy: Is human-associated Cyclospora a mammalian Eimeria species? Emerg Infect Dis 1997;3:381-383.
When freshly passed in stools, the oocyst is not infective (thus, direct fecal-oral transmission cannot occur; this differentiates Cyclospora from another important coccidian parasite, Cryptosporidium). 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 . Fresh produce and water can serve as vehicles for transmission and the sporulated oocysts are ingested (in contaminated food or water) . The oocysts excyst in the gastrointestinal tract, freeing the sporozoites which invade the epithelial cells of the small intestine . Inside the cells they undergo asexual multiplication and sexual development to mature into oocysts, which will be shed in stools . The potential mechanisms of contamination of food and water are still under investigation.
Cyclosporiasis has been reported in many countries, but is most common in tropical and subtropical areas. Since 1990, at least 11 foodborne outbreaks of cyclosporiasis, affecting approximately 3600 persons, have been documented in the United States and Canada.
After an average incubation period of 1 week, symptomatic infections typically manifest as watery diarrhea, which can be severe. Other symptoms include anorexia, weight loss, abdominal pain, nausea and vomiting, myalgias, low-grade fever, and fatigue. Untreated infections typically last for 10-12 weeks and may follow a relapsing course. Infections, especially in disease-endemic settings can be asymptomatic.
Cyclospora cayetanensis oocysts in wet mounts.
Currently, the most practical diagnostic method consists of the identification of oocysts in stool specimens by light microscopy. Although microscopy remains the method of choice in most clinical laboratories, molecular diagnosis using culture-independent diagnostic tests (CIDT), such as the FilmArray Gastrointestinal Panel by BioFire, has become increasingly more common.
Specimens should be preserved as soon as possible after collection. Various fixatives can be used depending on what tests will be performed.
- Stool fixed in 10% formalin is recommended for direct microscopy, concentration procedures, and preparation of stained smears; Specimens fixed in sodium acetate-acetic acid formalin can be handled in the same manner as specimens fixed in 10% formalin.
- Stool fixed in formalin-free fixatives, such as polyvinyl alcohol (PVA) or one-vial fixatives (e.g., TotalFix and EcoFix) is suitable forPCR-based detection and UV microscopy.
Unpreserved stool collected in enteric transport media (e.g., Cary-Blair) is commonly used for CIDTs and can be used for confirmatory testing by microscopy and/or PCR if needed. Unpreserved specimens must be refrigerated and sent to the diagnostic laboratory as rapidly as possible.
Cyclospora oocysts can be excreted intermittently and in small numbers. Thus:
- A single negative stool specimen does not rule out the diagnosis; three or more specimens at 2- or 3-day intervals may be required
- Concentration procedures should be used to maximize recovery of oocysts. The method most familiar to laboratorians is the formalin-ethyl acetate sedimentation technique (centrifuge for 10 minutes at 500 × g). Other methods can also be used (such as the Sheather’s flotation procedure).
The sediment can be examined microscopically with different techniques:
Several conventional and real-time PCR protocols have been developed to specifically detect Cyclospora cayetanensis in stool. CDC utilizes a real-time PCR that targets a region of the 18S rRNA gene using a species-specific TaqMan probe. When detecting C. cayetanensis in stool using PCR it is important to choose an appropriate DNA extraction technique that will adequately break open the oocysts; methods that include a vigorous bead beating step generally perform best.
- Eberhard ML, Pieniazek NJ, and Arrowood MJ. Laboratory diagnosis of Cyclospora infections. Arch Pathol Lab Med 1997;121:792-797.
- Verveij JJ, Laeijendecker D, Brienen EAT, van Lieshout L, Polderman, AM. Detection of Cyclospora cayetanensis in travellers returning from the tropics. International J Med Microbiol 2003: 293:199-202.
DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.