Cyclospora cayetanensis is a protozoon which belongs to to the Coccidia. Several related protozoa were described in moles and myriapods by Eimer (1870) and Schaudin (1901). It is closely related to Eimeria. It was named in 1994 by Ortega and collegues. The name is derived from the morphology (the sporocysts are spherical) and from a Peruvian university (most of the epidemiological and taxonomic work has been carried out at the Universidad Peruana Cayetano Heredia, Lima, Peru). Before 1992 the organism was wrongly regarded as a cyanobacterium. Distribution is probably cosmopolitan, but the species is only common in regions with poor hygiene.
After swallowing mature (i.e. sporulated) oocysts, there is excystation after contact with bile salts. The released sporozoites penetrate the jejunal enterocytes. In 1997 it was demonstrated that during infection of humans two different asexual stages occur as well as sexual stages. The full cycle can be completed in one host. Infected persons eliminate non-sporulated oocysts in their faeces. Until they sporulate, which takes days or weeks, these parasites cannot infect a new host. This delay makes direct human to human transmission improbable. After sporulation the oocyst contains 2 sporocysts each with 2 sporozoites. A reminder: In Isospora one oocyst has 2 sporocysts each with 4 sporozoites. Cryptosporidium oocysts contain no sporocysts, only 4 naked sporozoites.
Oocysts are spherical, measure 8-9 micron in diameter and contain granular material when excreted. At that point they are not yet sporulated (i.e. no sporozoits yet), and are not infectious. The oocysts to mature for a minimum of one week in the outside environment before becoming infectious. This implies that person-to-person transmssion would be very unlikely. The oocysts stain with varying degrees of acid fastness, but they are recognisable even without staining. They can be differentiated from Cryptosporidium oocysts because the latter are smaller (half the diameter). Isospora cysts are also acid-fast but are much larger (20-33 x 10-19 µm). Under UV light Cyclospora displays autofluorescence (blue with 355 nm dichroic filter and green with 450-490 nm filter). Isospora and Cryptosporidium do not autofluoresce. Fluorescence with auramine shows bright yellow disks in Cryptosporidium, but is weak in Cyclospora. Nevertheless in practice these more expensive techniques do not have to be used since diagnosis can be made using standard light microscopy.
The protozoa are present in the duodenum and jejunum and cause persistent watery diarrhoea, often accompanied by significant abdominal discomfort, nausea, tiredness and anorexia. The symptoms may last several weeks. In particular, non-immune persons such as travellers or small children, will be symptomatic. Cotrimoxazole is used in treatment. This protozoon also causes persistent diarrhoea in HIV-positive persons. If these cannot tolerate cotrimoxazole, the rather less effective ciprofloxacin may be used.
Knowledge about this parasite is insufficient. Transmission via water is possible and food may be contaminated by rinsing vegetables and fruit. Protozoa can be detected in surface water with special techniques. No reservoir is known to date. Similar parasites are found in primates and Cyclospora-like microorganisms have been found in ducks, chickens and dogs, but morphological similarity does not imply genetic identity.