Cyclospora cayetanensis

The classification of this parasite remained controversial for many years and the organism was often referred to as Cyanobacteria-like body or Coccidian-like body (CBL). In 1993, Y. Ortega definitively classified the parasite among intestinal coccidian protozoa, in the genus Cyclospora. The term “cayetanensis” comes from the University of Lima (Peru), named after Cayetano Heredia.

Infection with Cyclospora cayetanensis is a well known cause of diarrhea in many parts of the world. Transmission by contaminated food and water is very common. Although many other species of Cyclospora affect animals, none seems to infect man.

Infective oocysts excyst in the small intestine and the released sporozoites invade the enterocytes of the jejunum, where they settle inside an intracytoplasmic parasitophorous vacuole. There, the life cycle of the parasite takes place, with both an asexual and a sexual phase. The latter gives rise to immature oocysts, which are released with the feces.

Oocysts

Size: 8-10 μm.

Morphology: spherical.

Non-sporulated oocysts that are excreted with the feces are not infective. Sporulation takes place in the external environment in conditions of high temperature and humidity and requires a variable amount of time (from one to several weeks). The process leads to the formation of two sporocysts – each containing two sporozoites – inside the oocysts. Sporulation can be induced under laboratory conditions, maintaining a specimen of fresh feces in a 2.5% solution of potassium dichromate at a temperature between 27° and 32˚ C for 7-13 days.

On direct wet mount examination, oocysts appear as spherical elements, with a thick double wall. Often, inside the cysts is seen a greenish mass comprising 6-10 refractile globules 2 μm wide (morula). Stains suitable for temporary wet mounts are not useful. Specimen positivity always needs to be confirmed by modified Ziehl-Neelsen (hot) or Kinyoun (cold) staining to demonstrate that the oocysts are acid resistant. Unlike Cryptosporidium, oocysts of Cyclospora cayetanensis stain variably: some do not stain at all, while others stain light pink to red or dark purple. With safranin-based stains, all oocysts stains bright red, but only if the smear is preheated in a microwave oven.

A quick and easy method to detect oocysts in SAF- or formalin-fixed specimens is to examine the preparation under a fluorescence microscope, because the oocyst wall fluoresce with a bright blue color. To reduce the non-specific background fluorescence, a drop of Lugol's iodine solution should be added to the preparation.

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