Cyclospora: Review of an Emerging Parasite

Cyclospora: Review of an Emerging Parasite Gigi H. Brown, Pharm.D., and John C. Rotschafer, Pharm.D., FCCP Cyclospora is a parasite traditionally associated with diarrhea in travelers to endemic countries. Recently, several cases of cyclosporiasis were reported in nontravelers in the United States and Canada, implicating various fruits and vegetables as vehicles of infection. The life cycle of cyclospora is not fully known, but is believed to involve both asexual and sexual stages of proliferation. Food- and water-borne transmission of infection have been implicated. Patients infected with Cyclospora cayetanensis have protracted watery diarrhea. Various generalized symptoms are also present, making cyclosporiasis indistinguishable from infectious diarrhea caused by other microorganisms. Diagnosis depends on identifying the organism by microbiologic examination of stool samples. Treatment consists of supportive care, maintenance of fluid and electrolyte status, symptomatic relief, and antibiotic therapy. Trimethoprim-sulfamethoxazole is the only antibiotic available that is effective in eradicating the organism. (Pharmacotherapy 1999;19(1):70–75)

OUTLINE Microbiology Transmission Pathogenesis Physiology of Diarrhea Clinical Features and Diagnosis Treatment Summary

The parasite cyclospora is widely distributed throughout the world, and infection with it is associated with prolonged, watery diarrhea. 1 Cyclospora is not a new organism. It was first noted in the intestines of moles in 1881 and was identified as a cause of human infection in 1977 in Papua, New Guinea.2, 3 Before 1996 only three outbreaks of cyclosporiasis had been reported in the United States4–6; sporadic cases were limited to international travelers and immunocompromised adults. Due to recent outbreaks of infections in North America, cyclospora has emerged as a potential pathogen to all, regardless From the College of Pharmacy, University of Minnesota, Minneapolis, Minnesota, and the Department of Clinical Pharmacy, Regions Hospital, St. Paul, Minnesota (both authors). Address reprint requests to John C. Rotschafer, Pharm.D., Department of Clinical Pharmacy, Regions Hospital, 640 Jackson Street, St. Paul, MN 55101-2595.

of immunologic status or travel history. During the spring and summer of 1996 the Centers for Disease Control and Prevention reported 1465 sporadic and cluster-associated cases in the United States and Canada.7 Over 1600 cases were reported in the spring and summer of 1997.8 Illness has been attributed to the consumption of contaminated food; for example, imported raspberries, mesclun lettuce, and fresh basil. The occurrence of these outbreaks over the last 2 years challenges current methods of quality assurance in the produce industry abroad and highlights the relative lack of control the United States has on the importation of infected produce. It also has heightened our awareness of the potential of food- and water-borne illnesses in this country. Microbiology Cyclospora cayetanensis, a coccidian parasite, belongs to the subphylum Apicomplexa, family Eimeriidae. It is related to two other coccidian human enteric pathogens, cryptosporidia and isospora. Coccidian species can be differentiated by their shape, size, and morphology. 9, 10 Cyclospora spheroid oocysts are 8–10 µ in diameter, with each oocyst having two ovoid sporocysts that in turn enclose two sporozoites.

CYCLOSPORA Brown and Rotschafer Cyclospora oocytes are larger than cryptosporidia (spheroid, 4–6 µ) but smaller than isospora (ellipsoidal, 20–30 µ x 10–19 µ). Cryptosporidia have no sporocysts, whereas isospora have two, with four sporozoites per sporocyst. The life cycle of this species is not fully known. A generalized coccidian life cycle is depicted in Figure 1. It is thought to begin with ingestion of the oocyst, which, after exposure to gastric acid, bile, and pancreatic enzymes, releases its sporozoites into the gut lumen.11, 12 Sporozoites then invade enterocytes primarily in the small intestine. Enterocyte infection progresses through two stages, merogonic and sporogonic.11 The asexual merogonic stage involves maturation and development of sporozoites to schizonts that contain numerous forms called merozoites. Merozoites reproduce and multiply in infected cells. Rupture of infected epithelial cells frees

Figure 1. A generalized coccidian life cycle.

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merozoites, allowing infection to spread to other enterocytes in the host. The sporogonic stage then proceeds with merozoites undergoing sexual reproduction and gametogenesis to form oocysts. As enterocytes die, unsporulated oocysts are shed into the intestinal lumen to be excreted in stool. Cyclospora, in contrast to other coccidian species, require time outside the host for sporulation to take place. 9 Accordingly, approximately 40% of unsporulated oocysts may sporulate within 7–10 days on exposure to air and favorable environmental conditions.10 These mature oocysts may remain viable for months before contamination and exposure to host occurs, repeating the life cycle. Transmission Although the exact mechanism of contamination

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is unknown, both food- and water-borne transmission are considered major sources of infection of cyclospora. 4, 7, 13–15 In that the oocysts are noninfectious when excreted, direct person-to-person transmission is unlikely. 9 However, ingesting fecally contaminated water or food could cause an infection. Several reports attempting to identify sources of infection linked inadequately filtered water, untreated tap water, and stagnant water in storage tanks to many infections.4, 16–18 Another outbreak was blamed on ingestion of chlorine-treated water, suggesting that cyclospora, like cryptosporidia, is highly resistant to chlorine disinfection.13 One investigation speculated that produce farmers in Guatemala were constructing and maintaining water supplies near leaking sewage systems.7 The authors discovered that although attempts may be made to separate agricultural water supplies from growing crops, this contaminated water could be used later to dilute insecticides or pesticides that are sprayed directly on the produce. This food is eventually exported to the United States and other areas around the world. Berries, such as raspberries, have many crevices, making quick tap water washing often insufficient in removing the parasite, thus leading to exposure and infection.7 Unfortunately, due to the insensitivity and nonstandardization of current testing methods, determining exact modes of contamination in these cases was extremely difficult.19 Future means of eliminating contamination from fresh produce may include electrical and radioactive processes. 20 Irradiating food with ionizing energy from gamma rays greatly reduces bacterial and parasitic contamination of fruits and vegetables without decreasing their nutritional value or safety.21 Ionizing radiation exerts its effect by damaging microbial DNA and thus inhibiting normal biochemical processes.22 The U.S. Department of Agriculture, World Health Organization, and the U.S. Food and Drug Administration all advocate irradiation, but the food industry is not routinely using this method due to lack of consumer acceptance.22 Unfortunately, washing produce with tap water does little more than remove debris. Therefore, methods to reduce the risk of exposure to the consumer are limited at this time. Pathogenesis The pathogenesis of the infection and associated diarrhea are not fully elucidated.

Enterocytes are believed to be invaded by sporozoites, causing release of cytokines from epithelial cells.23 Cytokines, in turn, activate and recruit phagocytes from the blood. These phagocytes release factors such as histamine, prostaglandins, and platelet-aggregating factors that increase intestinal secretion of chloride and water and inhibit absorption.24, 25 Another mechanism of enterocyte damage, besides direct damage caused by the parasite, is inflammation; T cells, proteases, and oxidants secreted from mast cells are responsible for this process.23 Consequently, erythema of the distal duodenum has been observed during upper endoscopic procedures.26 Duodenal biopsies also revealed loss of brush border, partial atrophy of villi, crypt hyperplasia, and inflammation of the lamina propria. A few patients also showed Dxylose malabsorption.16, 26 Ultimately, marked destruction of enterocytes causes nutrient malabsorption and increased secretion of fluids and electrolytes from the gut, destruction that produces secretory and osmotic diarrhea.11 Physiology of Diarrhea Managing patients with diarrhea is often difficult. An initial step is understanding the physiology of diarrhea and assessing the cause. Four general mechanisms exist to disrupt water and electrolyte imbalance in the gastrointestinal tract and cause diarrhea: either decreased sodium absorption or heightened chloride secretion; increased luminal osmolarity; change in intestinal motility; and increase in tissue hydrostatic pressure. 27 Diarrhea of infectious origin usually involves secretory and/or osmotic components.11 Secretory diarrhea develops when a provoking substance (histamine, prostaglandins, plateletaggregating factor) either increases secretion or decreases absorption of large amounts of fluid and electrolytes.27 Large stool volumes in excess of 1 L/day, normal ionic contents, and plasmaequivalent osmolality usually result. Secretory diarrhea is unrelieved by avoiding solid food. Osmotic diarrhea results when inadequately absorbed substances (D-xylose) cause retention of intestinal fluids in order to maintain osmolality near plasma. 27 Unlike secretory diarrhea, it is relieved by fasting, and loss of sodium and water is usually less severe. Another step in diagnosis is assessing the duration of symptoms. Acute diarrhea is usually sudden in onset and associated with frequent,

CYCLOSPORA Brown and Rotschafer watery, loose stools, flatulence, and abdominal pain. 27 Symptoms usually subside within 72 hours of onset. Chronic diarrhea, on the other hand, involves frequent attacks over many extended periods.27 Weight loss, anorexia, and chronic weakness often coincide. Clinical Features and Diagnosis Clinical features of C. cayetanensis, specifically, vary. Patients may have an acute, self-limiting illness lasting a few days, or can develop chronic diarrhea extending over weeks. The diarrhea is usually watery and nonbloody, viscous, and khaki-green in color, and lacks inflammatory cells.1 Symptoms occur within 2–11 days after exposure to the parasite, however, the incubation period averages about 1 week.1 The diarrhea can be cyclic, alternating with bouts of constipation.9 Accompanying symptoms may include abdominal cramping, fever, fatigue, nausea, vomiting, anorexia, and weight loss. A prodromal syndrome of myalgias and arthralgias may develop before gastrointestinal symptoms occur. 1 Several reports claim an average of 4–6 stools/day and diarrhea lasting averages of 5 days–15 weeks in untreated, immunocompetent adults. 14, 16, 28–30 Diarrhea typically lasted longer in immunocompromised patients, with a mean duration of 4 months.31, 32 The majority of cases, regardless of host immune status, were self-limited and nonacute, meaning the symptoms resolved spontaneously. Few patients require hospitalizations, and only one death was reported, due to salmonellosis and Kaposi’s sarcoma in a patient positive for the human immunodeficiency virus (HIV). 15, 33 Remissions and relapses are common. In short, the clinical features of this infection may be indistinguishable from those of bacterial, viral, or parasitic infections, including other coccidian parasites. Therefore, health care professionals must rely on diagnostic indicators to differentiate among infectious agents. Diagnosis of cyclosporiasis relies on microbiologic identification of oocysts in stool and thorough knowledge of morphologic differences among coccidian species. Cyclospora oocysts appear as nonrefractile spheres 8–10 µ in diameter. 9 Isospora are ellipsoidal and much larger, with oocyst diameters of 20–30 µ x 10–19 µ. Cryptosporidia are spheric and half the diameter of cyclospora, but otherwise very difficult to differentiate. Therefore, oocyst diameters should always be measured. Cyclospora

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obtained from stools are immature and therefore will not contain visible sporocysts. 34 On the other hand, cryptosporidia mature in the host, and therefore sporocysts may be identified. Cyclospora oocysts, like cryptosporidia and isospora, are acid fast but have variable appearances, staining dark red or pink, or not staining at all.34 Some may contain granules or appear bubbly or wrinkled. As well, the oocysts autofluoresce under ultraviolet illumination, appearing as bright green to intense blue bodies. This characteristic, however, is not specific for cyclospora. Other currently available serologic or immunosorbent assays, including those to detect cryptosporidia, are not useful for cyclospora. Treatment Therapeutic goals in patients with cyclosporiasis consist of preventing excessive fluid and electrolyte disturbances, providing symptomatic relief, and treating the cause. Due to the selflimited nature of the infection, rehydration can be done orally and usually does not require intravenous fluids and hospitalization. With regard to symptomatic relief, it is important to remember that the defense mechanisms for ridding the body of the parasite may be disrupted if antidiarrheals are administered liberally, thus possibly prolonging or worsening the illness. According to several reports, antidiarrheals (loperamide hydrochloride), peristaltic regulators (metoclopramide), and histamine 2 -receptor blockers (ranitidine hydrochloride) are ineffective in reducing symptoms.35, 36 Therefore, palliative therapy with pain relievers, antipyretics, and other antacids and antiemetics may prove futile. Antibiotic therapy at this time is limited to trimethoprim-sulfamethoxazole (TMP-SMX), which is believed to inhibit parasitic synthesis of tetrahydrofolate and thereby disrupt nucleic acid synthesis. Sulfonamides inhibit dihydrofolic acid formation from para-aminobenzoic acid, and trimethoprim sequentially inhibits reduction of dihydrofolic acid to tetrahydrofolate. The combination of agents typically inhibits microbial tetrahydrofolate production more effectively than either drug alone and lessens the risk of resistance. In placebo-controlled trials, TMP-SMX was highly effective, resulting in both clinical and microbiologic cures. 14, 31 Symptoms resolved rapidly, often after 1 day of therapy A temporal

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relationship was also seen between improvement of symptoms and eradication of the parasite from stool. In immunocompetent patients, one tablet of TMP-SMX 160-800 mg twice/day for 7 days was statistically significantly better than placebo for cyclospora.14 Nine (45%) of 20 TMP-SMXtreated patients reported substantial improvement in symptoms on day 3 of therapy, versus only 3 (16%) of 19 placebo recipients. Only 1 (6%) of 16 TMP-SMX-treated patients was still excreting parasite on day 7 of therapy, versus 15 (88%) of 17 receiving placebo. Forty-three HIV-infected patients were treated with one TMP-SMX double-strength tablet 4 times/day for 10 days.31 Diarrhea and abdominal pain stopped in all patients after a mean of 2.5 days (range 1–5 days). Stool samples obtained on day 10 of therapy were negative for cyclospora in all patients, 100% eradication. Unfortunately for sulfa-allergic patients, no antibiotic alternatives exist that are clinically proved to eradicate the parasite. Of interest, trimethoprim alone is ineffective. Parasitic inhibition, therefore, may either be produced by the sulfonamide component of TMP-SMX or by synergistic activity of the combination. Metronidazole, norfloxacin, quinacrine, nalidixic acid, tinidazole, and diloxanide furoate actually extended the duration of symptoms 11 days beyond placebo.16 Ciprofloxacin and azithromycin are also ineffective. 37, 38 Pyrimethamine and albendazole have not been adequately studied. Furthermore, no in vitro or animal studies to date suggest efficacy of other classes of antibiotics. The benefit of desensitizing allergic patients has yet to be determined. Therefore, although no reports elaborate on specifics of rehydration (which agent, what volume, at which frequency), aggressive fluid replacement should be promoted in sulfa-allergic patients until the infection subsides. The decision to hospitalize and administer intravenous therapy should be based on clinical features, duration of symptoms, and underlying immune status. Practitioners should attempt symptomatic relief with agents such as acetaminophen, ibuprofen, prochlorperazine, or ondansetron until further studies or experience rule against their efficacy. Summary Clearly many unknowns regarding cyclospora require additional study. Complete understanding of the parasite’s life cycle and method of

transmission is crucial to preventing and treating the intestinal disease caused by the pathogen. Travelers for years have been warned against consuming water and produce abroad, however, 70% of selected fruits and vegetables consumed in the United States are imported from developing countries.39 Traveler’s diarrhea can occur without leaving home, so patients with persistent diarrhea should be tested for parasites regardless of travel history. As the number of outbreaks in the United States increases, it is imperative that an acceptable method of eliminating contamination of imported produce be developed. In the meantime, health care professionals should be acquainted with the signs and symptoms of cyclosporiasis and appropriate methods of diagnosis so that early detection and treatment in patients can abate the potential morbidity associated with the infection. References 1. Soave, R. Cyclospora: an overview. Clin Infect Dis 1996;23:429–37. 2. Levine ND. Taxonomy and life cycles of coccidia. In: Long PL, ed. The biology of the coccidia. London: Edward Arnold, 1982:1–33. 3. Ashford RW. Occurrence of an undescribed coccidian in man in Papua, New Guinea. Ann Trop Med Parasitol 1979;73: 497. 4. Huang P, Weber J, Sosin D, et al. The first reported outbreak of diarrheal illness associated with cyclospora in the United States. Ann Intern Med 1995;123(6):409–14. 5. Carter RJ, Guido F, Jacquette G, Rapoport M. Outbreak of cyclosporiasis at a country club—New York, 1995 [abstr]. In: The 45th annual Epidemic Intelligence Service (EIS) conference. Atlanta, GA: US Department of Health and Human Services, Public Health Service, 1996:58. 6. Koumans EH, Katz D, Malecki J, et al. Novel parasite and mode of transmission: cyclospora infection—Florida [abstr]. In: The 45th annual Epidemic Intelligence Service (EIS) conference. Atlanta, GA: US Department of Health and Human Services, Public Health Service, 1996:60. 7. Herwaldt BL, Ackers ML, and the Cyclospora Working Group. An outbreak in 1996 of cyclosporiasis associated with imported raspberries. N Engl J Med 1997;336:1548. 8. Centers for Disease Control and Prevention. Outbreak of cyclosporiasis—northern Virginia-Washington, D.C.-Baltimore, Maryland, metropolitan area, 1997. MMWR 1997;46(30): 689–91. 9. Soave R, Herwaldt BL, Relman DA. Cyclospora. Infect Dis Clin North Am 1998;12(1):1–12. 10. Marshall M, Naumovitz D, Ortega Y, et al. Waterborne protozoan pathogens. Clin Microbiol Rev 1997;10(1):67–85. 11. Goodgame R. Understanding intestinal spore-forming protozoa: cryptosporidia, microsporidia, isospora, and cyclospora. Ann Intern Med 1996;124:429–41. 12. Ackers J. Gut coccidia—isospora, cryptosporidium, cyclospora and sarcocystis. Semin Gastrointest Dis 1997;8(1):33–44. 13. Rabold J, Hoge C, Shlim D, et al. Cyclospora outbreak associated with chlorinated drinking water. Lancet 1994;344:1360. 14. Hoge C, Shlim D, Ghimire M, et al. Placebo-controlled trial of co-trimoxazole for cyclospora infections among travellers and foreign residents in Nepal. Lancet 1995;345:691–3. 15. Centers for Disease Control and Prevention. Update:

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