Cyclosporiasis

Cyclosporiasis is infection with the coccidian protozoan parasite, Cyclospora cayetanensis.

This organism can cause enteritis in both immunocompetent and immunocompromised hosts. Cyclospora is an acid-fast staining organism and has occasionally been mistaken for cryptosporidium (also acid-fast staining).

Cyclosporiasis typically induces periodic profuse watery diarrhoea.

Human C. cayetanensis infection has been documented in over 56 countries worldwide, and 13 of these have recorded cyclosporiasis outbreaks (1,2):

• C. cayetanensis is the only documented Cyclospora species known to infect humans
• most of these infections are contracted via the faecal-oral route, and water, berries, basil, cilantro, and other food produce can be a vehicle for Cyclospora transmission
• athough large outbreaks of cyclosporiasis have been documented in developed countries, C. cayetanensis infections are most commonly reported in developing countries or in endemic areas
• frequently the cyclosporiasis patient is an immunocompetent traveler living in an industrialized country, returning from a tropical and/or developing country such as the Dominican Republic, Mexico, Guatemala, Haiti, Peru, or Nepal, among others
  • typical symptoms on presentation include watery diarrhoea, abdominal cramps, vomiting, anorexia, weight loss, and severe fatigue
  • less frequently patients also report flu-like symptoms
  • is not endemic in the UK (3)
  • incubation period (3): usually 7 days (range 1-14 days)
• transmission (3):
  • direct person-to-person spread is unlikely
  • cyclospora cayetanensis is transmitted by ingesting infective oocysts. Oocysts are excreted in faeces of human hosts in a non-infective form. They must then sporulate (mature) over 7-15 days in the environment to become infective
  • ingestion of sporulated oocysts from sources such as drinking water, and fresh foods cause infection
  • outbreaks linked to imported fresh berries, herbs and salad leaves have been documented in developed countries
• in immunocompromised patients presentation may be with a severe, protracted, or chronic watery diarrhoea along with nausea, abdominal pain, mild fever, lethargy, and emaciation (2)
• diagnosis is based on cardinal clinical symptoms and conventional laboratory methods, which usually involve microscopic examination of wet smears, staining tests, fluorescence microscopy, serological testing, or DNA testing for oocysts in the stool
• trimethoprim-sulfamethoxazole for 7 to 10 days, is the antibiotic treatment of choice
  • in immunocompetent adults:
    • trimethoprim-sulfamethoxazole (TMP-SMX) (TMP 160 mg plus SMX 800 mg) orally, twice a day, for 7 – 10 days (4)
  • can evidently cure C. cayetanensis infection
  • reduces symptoms of diarrhoea within several days
  • in immunocompromised patients a prolonged antibiotic course may be required
  • if sulfonamide intolerance then ciprofloxacin, although less effective, is an alternative antibiotic option
  • nitazoxanide that can be used in the cases of sulfonamide intolerance and ciprofloxacin resistance

Notes (3):

• immunocompromised cases may remain infected for several months, but treatment will clear infection
• in a cluster/outbreak situation, a travel history should be sought and if none, a detailed food history (including raw fruits, salads, herbs and imported foods) should be undertaken

Reference:

1. Linder KA, Malani PN. What Is Cyclosporiasis? JAMA. Published online July 21, 2026. doi:10.1001/jama.2026.14866.
2. Li J, Cui Z, Qi M, Zhang L. Advances in Cyclosporiasis Diagnosis and Therapeutic Intervention. Front Cell Infect Microbiol. 2020 Feb 11;10:43.
3. PHE (2019). Recommendations for the Public Health Management of Gastrointestinal Infections.
4. Centers for Disease Control and Prevention. Clinical care of cyclosporiasis. Published February 27, 2024. Accessed August 5, 2026. https://www.cdc.gov/cyclosporiasis/hcp/clinical-care/index.html