The causal agent
has been only recently identified as a unicellular coccidian parasite.
The species designation Cyclospora cayetanensis was given in 1994
to Peruvian isolates of human-associated Cyclospora. It appears
that all human cases are caused by this species.
Some of the
elements in this figure were created based on an illustration by Ortega
et al. Cyclospora cayetanensis. In: Advances in Parasitology:
opportunistic protozoa in humans. San Diego: Academic Press; 1998. p.
freshly passed in stools, the oocyst is not infective
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
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
been reported in many countries, but is most common in tropical and
subtropical areas. Since 1990, at least 11 food-borne 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.
most practical diagnostic method consists of the identification of
oocysts in stool specimens by light microscopy. Other methods are also
available or under investigation.
be refrigerated and sent to the diagnostic laboratory as rapidly as
possible. If it is not possible to send the specimen to the laboratory
promptly, it should be preserved. Ideally, because a range of tests
might be desired, each of which has different requirements of the
specimen, the latter should be split in portions which should be
fixed in 10%
formalin (for direct microscopy, concentration procedures, and
preparation of stained smears);
fixed in 2.5%
potassium dichromate (for sporulation assays and molecular
fixation (for molecular diagnosis).
fixed in sodium acetate-acetic acid formalin can be handled in the same
manner as specimens fixed in formalin; however, specimens fixed in
polyvinyl alcohol (PVA) are of limited value because they are not usable
for concentration procedures.)
oocysts can be excreted intermittently and in small numbers. Thus:
negative stool specimen does not rule out the diagnosis; three or
more specimens at 2- or 3-day intervals may be required
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
The sediment can be examined microscopically with different techniques:
wet mounts (by
conventional light microscopy, which can be enhanced by UV
fluorescence microscopy or differential interference contrast (DIC,
(using modified acid-fast stain or a modified safranin stain)
Bench aids for
treatment for cyclosporiasis is a combination of two antibiotics,
trimethoprim-sulfamethoxazole*, also known as Bactrim, Septra, or
Cotrim. Supportive measures include management of fluid and electrolyte
balance, and rest.
* This drug is
approved by the FDA, but considered investigational for this purpose.