Sunday 9 January 2011

Cyclospora cayetanensis

Cyclospora cayetanensis
(Cyanobacterium-Like Body/Coccidian-Like Body/CLB)
Coccidian Protozoan Parasite

Though the genera Cyclospora has been known about for some time as pathogen of vertebrates, this nasty little species began to be increasingly reported in humans in the late 1970’s. First thought to be associated with blue-green algae, it was referred to as a Cyanobacterium-Like body. Others thought it was a larger variant of Cryptpsporidum. The organism was finally identified as belonging to the genus Cyclospora based on sporulation studies which revealed that each oocyst contains two sporocysts which in turn contain two sporozoites.

Cyclospora can be found worldwide however it may exhibit greater prevalence in rainy areas where outbreaks coincide with the rainy season. Infection is primarily acquired by ingestion of water bearing the oocyst or produce which has been irrigated with contaminated water. There is no proof of person to person infection as the oocyst needs about 10 days outside of the body to mature and become infective.

On ingestion, the oocyst takes up residence within cells (enterocytes) of the small intestine. Cyclospora appears to have both asexual and sexual reproduction with the infective oocyst being the product of sexual reproduction. The invasion of the intestinal enterocytes is thought to stimulate cytokine production which causes inflammation, electrolyte secretion and ultimately osmotic diarrhoea.

Otherwise healthy individuals may suffer a prolonged, yet self-limiting watery diarrhoea. Symptoms may include vomiting, nausea, fatigue, anorexia, fever, cramping and weight loss. Episodes of diarrhoea may alternate with constipation. Symptoms may begin 2 to 10 days after exposure and may last up to 7 weeks.
In immunocompromised patients such as those with AIDs, the illness can persist longer and have devastating consequences.

Diagnosis and Identification;
The organism is shed irregularly so stool specimens should be collected periodically if Cyclspora is suspected. The organism can be identified by several means including;

  • Wet-preps of formalin-ether concentrates - the spherical organisms are about 8 to 12 µm and appear refractile in unstained preparations.
  • Cyclospora exhibits variable acid-fast properties and organisms will stain to various degrees from virtually unstained through increasingly intense shades of pink. Stained oocyst may appear slightly smaller than the unstained 8 to 12 µm due to shrinkage. Cells often display a folded or wrinkled appearance. Cyclospora does not stain well with the Trichrome method.
  • Cyclospora will auto fluoresce under ultra-violet light, appearing greenish under 450 nm wavelength and bluish under 365 nm.
Septra (Trimethoprim-Sulfamethoxazole) is commonly used in treatment.

Note: Cyclospora have been known to survive routine chlorination treatment.

(click on photo to enlarge for better viewing)

Above: Cyclspora cayetanensis as stained by the modified Iron-Hematoxylin staining method.
Organism exhibits variable acid-fastness thereby appearing clear/unstained right through various intensities of pink. Note too the wrinkled or folded appearance the organism can have in the stained preparation. Wrinkling and a slightly smaller diameter may be due to shrinkage during the staining process. (photos X1000 oil immersion)

(click on photo to enlarge for better viewing)

Formalin-ether stool concentrate wet preparation showing unstained Cyclospora cayetanensis.

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