General Characteristics

During the past few years, a number of outbreaks of diarrhea associated with Cyclospora cayetanensis have occurred; the distribution is worldwide (United States, Caribbean, Central and South America, Southeast Asia, Eastern Europe, Australia, Nepal). These organisms are acid-fast variable and have been found in the feces of immunocompetent travelers to developing countries, immunocompetent individuals with no travel history, and patients with AIDS. Cumulative evidence suggests that outbreaks in the United States and Canada during the spring months of 1996 and 1997 were related to the importation and ingestion of Guatemalan raspberries. An outbreak in Florida in 1995 quite likely was also attributable to contaminated food. The cases reported in all three out breaks probably represented only a small fraction of incidences.

The life cycle of C. cayetanensis involves only humans as hosts. Oocysts are passed in the feces unsporulated (Figure 1). At room temperature (23° to 25°C), small numbers of oocysts may sporulate within 10 to 12 days.

Fig1. A, Cyclospora cayetanensis oocysts after modified acid-fast staining. Note the variability in the intensity of the stain. These  oocysts measure 8 to 10 µm, twice the size of Cryptosporidium spp. (oil immersion, ×1000). B and C, Cyclospora cayetanensis oocysts  exhibiting autofluorescence (high dry power, ×400). (A and B courtesy Charles R. Sterling, University of Arizona; C courtesy E. Long, Centers  for Disease Control and Prevention, Atlanta, Ga.)

In clean wet mounts, Cyclospora organisms are seen as nonrefractile spheres, which are difficult to recognize as parasites. Unless a high number of oocysts are present, they may easily be mistaken for artifacts. They are acid fast variable with the modified acid-fast stain; those that are unstained appear as glassy, wrinkled spheres (wrinkled cellophane). The oocysts are twice the size of those of Cryptosporidium spp. and measure 8 to 10 µm in diameter. Because it takes 10 days to 2 weeks for the oocysts to sporulate, no internal structures are visible (sporozoites), as can be seen in Cryptosporidium organisms.

Epidemiology

 Transmission of C. cayetanensis is thought to be by the fecal-oral route. However, direct person-to-person trans mission has not been well documented and may not be a factor, because sporulation takes a number of days. Outbreaks linked to contaminated water and various types of fresh produce (raspberries, basil, baby lettuce leaves, and snow peas) have been reported. Information on reservoir hosts is not well defined; however, in some areas humans appear to be the only host.

C. cayetanensis is endemic in Central and South America, the Caribbean, Mexico, Indonesia, Asia, Nepal, Africa, India, Southern Europe, and the Middle East. In endemic areas, contact with soil and water increases the risk of Cyclospora infection. Infections in most temperate areas are correlated with the consumption of imported contaminated fruits and vegetables,

Pathogenesis and Spectrum of Disease

 Although some patients are asymptomatic, others report a flulike illness, marked by nausea, vomiting, anorexia, weight loss, and explosive diarrhea lasting 1 to 3 weeks. The incubation period is not yet known. However, the onset of symptoms after infection generally averages 7 to 8 days, and the symptoms last 2 to 3 weeks. Oocyst shedding in the feces is highly variable and may range from 7 days to several months. Indigenous infections are confined primarily to tropical, subtropical, or warm temperate regions of the world. Outbreaks occur in other areas of the world as a result of contaminated foodstuffs.

In immunocompromised and immunocompetent patients, C. cayetanensis infection can be associated with biliary disease. With light and transmission electron microscopy, developmental stages have been seen in the gallbladder epithelium of AIDS patients with acalculous cholecystitis. Also, oocysts have been seen in the bile of patients with active biliary disease.

Laboratory Diagnosis

 C. cayetanensis oocysts do not routinely stain with the trichrome fecal stain; special methods are required for identification. The oocysts can be concentrated using routine methods; special stains can then be used to enhance morphology. A single negative stool specimen is not conclusive in the examination of stools for coccidia; a total of three stool specimens collected on sub sequent days must be examined before infection can be ruled out.

Special Stains. With modified acid-fast stains, the oocysts appear light pink to deep red, and some contain granules or have a bubbly appearance (described as wrinkled cellophane). It is very important to be aware of these organisms when the modified acid-fast stain is used, because Cryptosporidium spp. and other similar but larger structures (approximately twice the size of Cryptosporidium oocysts [8 to 10 µm]) are seen in the stained smear. Laboratories need to measure all acid-fast oocysts, particularly if they appear to be somewhat larger than those of Cryptosporidium spp. Variations on the safranin staining technique stain C. cayetanensis oocysts orange or pinkish orange, and heating and other treatments have been used to increase the staining frequency of oocysts. The oocysts autofluoresce green (450 to 490 DM excitation filter) or blue (365 DM excitation filter) under ultraviolet (UV) epifluorescence. It is strongly recommended that during concentration (formalin ethyl acetate) of stool specimens, centrifugation be carried out for 10 minutes at 500× g. The concentration sediment can then be stained, enhancing the sensitivity of the microscopy examinations.

Flow Cytometry. Flow cytometry is another diagnostic option. This approach appears to be a useful alternative to microscopy, particularly for screening large numbers of clinical specimens for Cyclospora oocysts in an outbreak situation. However, it is not commonly used.

Other Diagnostic Methods. Although culture, antigen detection, nucleic acid detection, and serologic tests for antibody have been developed, none of these methods is routinely available for most clinical laboratories.

Therapy

Patients have been treated symptomatically with antidiarrheal preparations and have obtained some relief; however, the disease appears to be self-limiting within a few weeks. Trimethoprim (TMP-SMX), currently the drug of choice, is given orally twice daily for 7 days. Elimination of parasites, a decrease in diarrhea, and diminished abdominal pain occur within 2 to 3 days after treatment. Patients with AIDS may need higher doses and long-term maintenance treatment. However, more than 40% of patients have a recurrence of symptoms in 1 to 3 months after treatment.

Prevention

Individuals in endemic areas should wear gloves when gardening to prevent exposure to oocysts of C. cayetanensis. Thorough washing of produce may help remove oocysts. Most of the produce items implicated in the transmission of C. cayetanensis are consumed raw; thus cooking as a means of prevention is not relevant.

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