Cyclospora cayetanensis

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This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Cyclosporiasis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]


Cyclospora cayetanensis is a protozoan that causes disease in humans, and possibly in other primates. It has also been isolated from the feces of other animals such as ducks and chickens. Due to the spherical shape of C. cayetanensis sporocytes, it was placed in the Cyclospora genus. It has a double layered wall that gives it resistance against disinfectants and adhesins which are responsible for its adherence characteristics. The bacteria show tropism for epithelial cells of the small intestine, especially of the duodenum and jejunum.


Three uniformly stained Cyclospora cayetanensisoocysts in the field of view. Image provided by the CDC Centers for Disease Control and Prevention [1]
Photomicrograph of a fresh stool sample, which had been prepared using a 10% formalin solution, and stained with modified acid-fast stain, revealed the presence of four Cyclospora cayetanensis oocysts in the field of view Image provided by the CDC Centers for Disease Control and Prevention [2]

Eukaryota; Alveolata; Apicomplexa; Conoidasida; Coccidia; Eucoccidiorida; Eimeriorina; Eimeriidae; Cyclospora[3]


Cyclospora cayetanensis is an obligate intracellular apicomplexan, cyst-forming coccidian protozoan, of the family of Eimeriidae, which commonly causes self-limiting diarrhea. Morphologically C. cayetanensis has spherical oocysts that are between 7.5 and 10 micrometers in diameter that also have a 50 nanometer thick bilayered wall with an outer threadlike coat that has been called a wrinkle by some researchers.[4][5][6]

According to a phylogenetic analysis performed with the 18S rRNA gene, in the Cyclospora species isolated from a group of baboons, this species, although different, was proved to be similar to the C. cayetanensis that infects humans. These two species were then documented was belonging to the same clade of the Eimeria species.[7] Other three species of Cyclospora were also identified in non-human primates and characterized with the SSU rRNA analysis, later that year. Because there are morphologically similar, there can not be differentiated by light microscopy.[8] These species: C. cercopitheci, C. colobi and C. papionis were identified in green monkeys, colobus monkeys, and baboons, respectively. C. cayetanensis and these three other species of Cyclospora all share the characteristic of being host-specific.[5][5]

It is not known the exact conditions and location required for the sporulation of oocysts in the natural environment, however, these data would help to understand and predict the distribution and seasonality of C. cayetanensis. Due to its double-layered wall it is highly resistant, particularly to disinfectants used during food processing. This resistance along with its binding affinity to certain produce, explains the risks associated with contaminated foods. The adhesive properties of C. cayetanensis are stronger than those of the oocysts of Giardia or Cryptosporidium, however, the responsible adhesins are yet to be identified.[5]


Cyclospora cayetanensis shows tropism for epithelial cells of the small intestine, especially for the jejunum.[5]

Natural Reservoir

C. cayetanensis is an host specific parasite that is able to infect humans. Cyclospora oocysts have also been isolated from the feces of several animals, such as ducks, chickens and dogs.[9][10][11] Attempts to identify and to infect different animals with C. cayetanensis have failed.[12] Certain shellfish may acquire C. cayetanensis from contaminated waters, and concentrate its oocyst for several days.[13]

Differential diagnosis

Cyclospora cayetanensis infection must be differentiated from other causes of viral, bacterial, and parasitic gastroentritis.

Organism Age predilection Travel History Incubation Size (cell) Incubation Time History and Symptoms Diarrhea type8 Food source Specific consideration
Fever N/V Cramping Abd Pain Small Bowel Large Bowel Inflammatory Non-inflammatory
Viral Rotavirus <2 y - <102 <48 h + + - + + - Mostly in day cares, most common in winter.
Norovirus Any age - 10 -103 24-48 h + + + + + - Most common cause of gastroenteritis, abdominal tenderness,
Adenovirus <2 y - 105 -106 8-10 d + + + + + - No seasonality
Astrovirus <5 y - 72-96 h + + + + + Seafood Mostly during winter
Bacterial Escherichia coli ETEC Any age + 108 -1010 24 h - + + + + - Causes travelers diarrhea, contains heat-labile toxins (LT) and heat-stable toxins (ST)
EPEC <1 y - 10 6-12 h - + + + + Raw beef and chicken -
EIEC Any ages - 10 24 h + + + + + Hamburger meat and unpasteurized milk Similar to shigellosis, can cause bloody diarrhea
EHEC Any ages - 10 3-4 d - + + + + Undercooked or raw hamburger (ground beef)  Known as E. coli O157:H7, can cause HUS/TTP.
EAEC Any ages + 1010 8-18 h - - + + + - May cause prolonged or persistent diarrhea in children
Salmonella sp. Any ages + 1 6 to 72 h + + + + + Meats, poultry, eggs, milk and dairy products, fish, shrimp, spices, yeast, coconut, sauces, freshly prepared salad. Can cause salmonellosis or typhoid fever.
Shigella sp. Any ages - 10 - 200 8-48 h + + + + + Raw foods, for example, lettuce, salads (potato, tuna, shrimp, macaroni, and chicken) Some strains produce enterotoxin and Shiga toxin similar to those produced by E. coli O157:H7
Campylobacter sp. <5 y, 15-29 y - 104 2-5 d + + + + + Undercooked poultry products, unpasteurized milk and cheeses made from unpasteurized milk, vegetables, seafood and contaminated water. May cause bacteremia, Guillain-Barré syndrome (GBS), hemolytic uremic syndrome (HUS) and recurrent colitis
Yersinia enterocolitica <10 y - 104 -106 1-11 d + + + + + Meats (pork, beef, lamb, etc.), oysters, fish, crabs, and raw milk. May cause reactive arthritis; glomerulonephritis; endocarditis; erythema nodosum.

can mimic appendicitis and mesenteric lymphadenitis.

Clostridium perfringens Any ages > 106 16 h - - + + + Meats (especially beef and poultry), meat-containing products (e.g., gravies and stews), and Mexican foods. Can survive high heat,
Vibrio cholerae Any ages - 106-1010 24-48 h - + + + + Seafoods, including molluscan shellfish (oysters, mussels, and clams), crab, lobster, shrimp, squid, and finfish. Hypotension, tachycardia, decreased skin turgor. Rice-water stools
Parasites Protozoa Giardia lamblia 2-5 y + 1 cyst 1-2 we - - + + + Contaminated water May cause malabsorption syndrome and severe weight loss
Entamoeba histolytica 4-11 y + <10 cysts 2-4 we - + + + + Contaminated water and raw foods May cause intestinal amebiasis and amebic liver abscess
Cryptosporidium parvum Any ages - 10-100 oocysts 7-10 d + + + + + Juices and milk May cause copious diarrhea and dehydration in patients with AIDS especially with 180 > CD4
Cyclospora cayetanensis Any ages + 10-100 oocysts 7-10 d - + + + + Fresh produce, such as raspberries, basil, and several varieties of lettuce. More common in rainy areas
Helminths Trichinella spp Any ages - Two viable larvae (male and female) 1-4 we - + + + + Undercooked meats More common in hunters or people who eat traditionally uncooked meats
Taenia spp Any ages - 1 larva or egg 2-4 m - + + + + Undercooked beef and pork Neurocysticercosis: Cysts located in the brain may be asymptomatic or seizures, increased intracranial pressure, headache.
Diphyllobothrium latum Any ages - 1 larva 15 d - - - + + Raw or undercooked fish. May cause vitamin B12 deficiency

8Small bowel diarrhea: watery, voluminous with less than 5 WBC/high power field

Large bowel diarrhea: Mucousy and/or bloody with less volume and more than 10 WBC/high power field
† It could be as high as 1000 based on patient's immunity system.

The table below summarizes the findings that differentiate inflammatory causes of chronic diarrhea[14][15][16][17][17]

Cause History Laboratory findings Diagnosis Treatment
Diverticulitis Abdominal CT scan with oral and intravenous (IV) contrast bowel rest, IV fluid resuscitation, and broad-spectrum antimicrobial therapy which covers anaerobic bacteria and gram-negative rods
Ulcerative colitis Endoscopy Induction of remission with mesalamine and corticosteroids followed by the administration of sulfasalazine and 6-Mercaptopurine depending on the severity of the disease.
Entamoeba histolytica cysts shed with the stool detects ameba DNA in feces Amebic dysentery

Luminal amebicides for E. histolytica in the colon:

For amebic liver abscess:


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