Case 1 -
Cyclospora Cayetanensis Enteritis
Rhonda K. Yantiss
Weill Medical College of Cornell University
New York, NY
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The patient is a 45 year-old HIV-positive male who presented
to the emergency room with severe dehydration following several months of profuse watery diarrhea, 10-15
bowel movements per day, and a 30-pound weight loss. The patient had a 9-year history of HIV infection,
but maintained stable CD4 counts (730) on anti-retroviral therapy, and had no known opportunistic
infections. He carried a diagnosis of ulcerative colitis that was made 12 months prior to
presentation, based upon clinical symptoms of increased stool frequency (6-8 non-bloody bowel
movements/day), endoscopic evidence of pancolitis, and colonic mucosal biopsies that showed
"non-specific" colitis. His symptoms initially improved with asacol and prednisone, but he continued to
have intermittent diarrheal episodes, the most recent of which occurred three months prior to
presentation. At that time, he developed severe diarrhea following a 5-day trip to Peru and was
empirically treated for amebiasis. He received a four-week course of metronidazole and, although
his diarrheal symptoms initially abated, they recurred following cessation of antibiotic therapy.
At the time of admission, the patient appeared thin and wasted, but had no localizing symptoms.
Laboratory findings included a normal hematocrit, normal white blood cell count with a slight
eosinophilia, and normal blood chemistries. Other pertinent studies included a negative C. difficile toxin assay and stool cultures with rare white cells.
Endoscopic examination of the upper and lower gastrointestinal tract revealed a slightly irregular
Z-line, but no other abnormalities. Mucosal biopsy samples were obtained from the jejunum,
duodenum, stomach, esophagus, ileum, and colon. The images provided depict the jejunal findings.
Cyclospora cayetanensis enteritis
Cyclospora cayetanensis was first recognized as a human pathogen by Ashford, who reported
its occurrence in Papua New Guinea in 1979 . This protozoal pathogen was further characterized in
the mid-1990s following several outbreaks of diarrheal illness in North America and Europe
Outbreaks in developed countries have been linked to waterborne sources and foods imported from
developing countries, such as raspberries and basil, where its transmission is probably due to
contaminated water supplies and poor sanitation . Children in endemic countries are five times more
likely to be infected than adults. Risk factors for infection include drinking or swimming in
contaminated water sources, direct contact with soil, and diets rich in raw, or poorly cooked, bivalves.
Humans are the only known hosts for Cyclospora cayetanensis6.
Cyclospora cayetanensis is an obligate intracellular parasite
that infects the duodenum and jejunum. The life cycle begins with ingestion of sporulated oocysts
that each contain two sporozoites, which are released upon excystation within the gut. The
sporozoites invade the intestinal epithelium and undergo at least two cycles of asexual reproduction
(merogony) within the cell, forming meronts that contain numerous merozoites8. First generation
meronts contain 8-12 merozoites and may undergo additional cycles of asexual reproduction. Second
generation meronts each contain four merozoites that are individually released to penetrate other
epithelial cells and subsequently form gametes via gametogony. The gametes enlarge to become
either female or male macrogamonts. The latter undergo meiosis to form numerous flagellated
microgametes, which are released to fertilize macrogamonts. The resulting zygote contains two
sporocysts and becomes enveloped in a resilient oocyst wall that is passed in the stool.
Sporulation occurs in the environment and is complete within 1-2 weeks, although some evidence
suggests that this stage of development may also occur within the human host8.
Clinical Features and Treatment
Cyclospora cayetanensis infection usually produces
symptoms within 2 weeks of exposure to the pathogen. Gastrointestinal symptoms include loose or
watery diarrhea, nausea, vomiting, cramps, flatulence, bloating, and weight loss, but most patients also
have systemic manifestations, such as fever, chills, myalgias, and fatigue. Cyclospora cayetanensis may infect either immunocompetent individuals, in whom it
produces a self-limited diarrheal illness, or immunodeficient patients, who may suffer life-threatening
or protracted symptoms. Trimethoprim-sulfamethoxazole is the standard treatment for cyclosporiasis, and
symptoms usually begin to resolve within 1-2 days of treatment initiation. Immunocompetent patients
receive a one-week course of twice-daily oral therapy, whereas those with immunodeficiency receive oral
doses four times daily for a 10-day period. Prolonged infection may result in biliary disease,
acalculous cholecystitis, Guillain-Barré syndrome, or reactive arthritis
Diagnosis and Pathologic Features
Cyclospora cayetanensis may be diagnosed using
several methods, including PCR-based assays for C. cayetanensis DNA.
Oocysts may be observed in stool samples or intestinal aspirates from infected patients.
They are non-refractile and show variable staining with a modified acid-fast stain, which is most
intense when performed on fresh specimens. The cysts also show bright autofluorescence under
ultraviolet illumination. Mucosal biopsy samples from the jejunum and distal duodenum show
variable degrees of villous shortening and crypt hyperplasia in association with patchy, usually mild,
increased inflammation in the lamina propria and crypt epithelium. The organisms are readily apparent on
routine hematoxylin and eosin stained sections, and all of the intracellular stages of the life cycle may
be identified. The asexual stages of the life cycle are distinct: first generation meronts contain
numerous merozoites ranging from 3-4 m m, whereas second generation meronts contain four larger (12-15 m
m) merozoites arranged in parallel arrays. Supranuclear parasitophorous vacuoles are often
numerous in the apical compartment of the epithelial cells and contain either sporozoites or mature, free
The oocysts of Cyclospora cayetanensis are morphologically similar to those of Cryptosporidium parvum and hominis, and may cause diagnostic confusion when evaluating stool samples.
However, the oocysts of the former are much larger (8-10 mm) than those of the latter (4-5 mm), and
the appearances of these pathogens in mucosal biopsy samples are entirely different. Cyclospora are deep-seated intracellular organisms that show various stages of
sexual and asexual reproduction, whereas Cryptosporidia are uniform
spherical structures that adhere to the luminal surface of the intestinal epithelium, but do not reside
within the cytoplasm . The parasitophorous vacuoles of Cyclospora
cayetanensis may also simulate the appearance of Isospora belli in
tissue sections. However, I. belli cysts are
elliptoid, elongated or crescentic in shape, and are much larger (20-33 x 10-19 m m) than those of C. cayetanensis. Thus, the distinction between these parasites is
straightforward when one combines morphologic assessment of mucosal biopsy samples and stool studies.
- Cyclospora cayetanensis is an obligate intracellular parasite that infects the duodenum and jejunum
- It must be differentiated from other coccidians such as Cryptosporidium and Isospora.
- Ashford RW: Occurrence of an undescribed coccidian in man in Papua New Guinea. Ann Trop Med Parasitol 1979, 73:497-500
- Connor BA, Johnson EJ, Soave R: Reiter syndrome following protracted symptoms of Cyclospora infection. Emerg Infect Dis 2001, 7:453-4
- Herwaldt BL: Cyclospora cayetanensis: a review, focusing on the outbreaks of cyclosporiasis in the 1990s. Clin Infect Dis 2000, 31:1040-57
- Herwaldt BL, Ackers ML: An outbreak in 1996 of cyclosporiasis associated with imported raspberries. The Cyclospora Working Group. N Engl J Med 1997, 336:1548-56
- Huang P, Weber JT, Sosin DM, et al.: The first reported outbreak of diarrheal illness associated with Cyclospora in the United States. Ann Intern Med 1995, 123:409-14
- Karanja RM, Gatei W, Wamae N: Cyclosporiasis: an emerging public health concern around the world and in Africa. Afr Health Sci 2007, 7:62-7
- Ortega YR, Gilman RH, Sterling CR: A new coccidian parasite (Apicomplexa: Eimeriidae) from humans. J Parasitol 1994, 80:625-9
- Ortega YR, Nagle R, Gilman RH, et al.: Pathologic and clinical findings in patients with cyclosporiasis and a description of intracellular parasite life-cycle stages. J Infect Dis 1997, 176:1584-9
- Ortega YR, Sterling CR, Gilman RH, et al.: Cyclospora species--a new protozoan pathogen of humans. N Engl J Med 1993, 328:1308-12
- Richardson RF, Jr., Remler BF, Katirji B, et al.: Guillain-Barre syndrome after Cyclospora infection. Muscle Nerve 1998, 21:669-71
- Shields JM, Olson BH: Cyclospora cayetanensis: a review of an emerging parasitic coccidian. Int J Parasitol 2003, 33:371-91
- Sun T, Ilardi CF, Asnis D, et al.: Light and electron microscopic identification of Cyclospora species in the small intestine. Evidence of the presence of asexual life cycle in human host. Am J Clin Pathol 1996, 105:216-20
- Zar FA, El-Bayoumi E, Yungbluth MM: Histologic proof of acalculous cholecystitis due to Cyclospora cayetanensis. Clin Infect Dis 2001, 33:E140-1