Coccidian parasites -Cyclospora cayetanensis

Basic description of C. cayetanensis regarding its morphology, Life cycle, Pathogenesis, Clinical Manifestations, and Laboratory diagnosis.

1. COCCIDIAN PARASITES  Cyclospora cayetanensis Dr. Suprakash Das Assit . Prof.

2. Cyclospora cayetanensis C. caytanensis is the only species of the genus that is cause to infection in human. Infection of GI tract in both immunocompetent and immunocompromised hosts. First discovered in 1979 in the human faeces , it has become an important parasite for AIDS patients. During the past few years, there have been several outbreaks of diarrhea associated with C. cayetanensis ; the distribution is worldwide (United States, Caribbean, Central and South America, Southeast Asia, Eastern Europe, Australia, Nepal).

3. Morphology Diagnostic forms in humans Cyclospora oocyst - these are excreted in the human faeces . These are round to oviod structures and measures 8-10 µm in diameter, variably Acid-fast and has blue-green flourescence . Sporulating oocyst - It is the Infective form to humans. Each oocyst contains 2 Sporocysts , each measuring 4 µm in diameter and containing 2 Sporozoites .

4. Life Cycle Humans acquire infection by the ingestion of water or vegetables contaminated with the sporulating oocyst - each oocyst contain 4 sporozoites . In the intestine, the oocyst releases sporozoites , which invade the enterocytes . Multiple fission by the sporozoites inside enterocytes produce Meronts which in turn are developed to Merozoites . Two types of Meronts and sexual stages have been seen in jejunal enterocytes

5. Life Cycle Merozoites divide to form Macrogametes (Female form) and Microgametes ( Male form) and reproduce to form new oocyst . It takes approximately 5 days or more for oocyst maturation , so the mature stage may not have been seen in human specimens. Also, information on potential reservoir hosts has yet to be defined; however, it appears that in some areas the human is the only host . Small intestine shows acute and chronic inflammation , blunting and atrophy of villi , and hyperplasia of crypts.

6. Clinical Features Developmental stages of C. cayetanensis usually occur within epithelial cells of the jejunum and lower portion of the duodenum. Cyclospora infection reveals characteristics of a small bowel pathogen, including upper gastrointestinal symptoms, malabsorption of d- xylose , weight loss, and moderate to marked erythema of the distal duodenum . Histopathology in small bowel biopsy specimens reveals  Acute and chronic inflammation, Partial villous atrophy, Crypt hyperplasia.

7. Clinical Features The incubation period is approximately 2 to 11 days after exposure. There is generally 1 day of malaise and low-grade fever, with rapid onset of diarrhea of up to seven stools per day. There may also be fatigue, anorexia, vomiting, myalgia, and weight loss with remission of self-limiting diarrhea in 3 to 4 days , followed by relapses lasting from 4 to 7 weeks.

8. Clinical Features In patients with AIDS , symptoms may persist for as long as 12 weeks; biliary disease has also been detected in this group. Diarrhea alternating with constipation has also been reported. Clinical clues include unexplained prolonged diarrheal illness during the summer in any patient and in persons returning from tropical areas. The majority of infected individuals had intermittent diarrhea for 2 to 3 weeks, and many complained of intense fatigue, as well as anorexia and myalgia , during the illness. The clinical presentation of patients infected with this organism is similar to that of patients infected with Cryptosporidium .

9. Epidemiology WORLD It is found in warm climates, mainly the tropics and subtropics. It is endemic in Nepal, Peru, Haiti, with a seasonal predominance in Rainy or Summer months. It is now also prevalent in Peurto Rico, Mexico, Indonesia, Morocco. INDIA Sporadiac cases are reported from Vellore, Puducherry , New Delhi and Benguluru .

10. Epidemiology Reservoir, Source and Transmission Human are the only reservoir of infection. Sporulating oocysts are infective stages. Water or vegetables, Fruits like Raspberries that are contaminated with sporulating oocysts are the sources of infection.

11. Diagnosis Parasitic Diagnosis- It is based on the – 1] Direct wet mount microscopic detection of ooocyst in faecal specimen. 2] Phase contrast microscopy 3] Autoflurescence with UV lights 4] Acid-fast staining methods. 5] LPCB mount The Cyclospora oocysts are excreted intermediately and in small numbers , so at least 2-3 stool specimens at 2-3 days interval is necessary to detect positive cases.

12. Diagnosis Formalin-ethyl acetate sedimentation technique and Sheather’s sucrose flotation methods are frequently used to concentrate the oocyst in the stool. Molecular method - A nested PCR assay tergetting the small sub-unit ribosomal RNA is employed for the diagnosis of Cyclospora infection.( 62% sensitivity).

13. Cyclospora cayetanensis oocyst in wet mount

14. Cyclospora cayetanensis oocysts  Modified acid-fast stain (A), Differential interference contrast microscopy of wet mount (B), Epifluorescence microscopy (330–380 nm ultraviolet excitation filter) (C).

15. Treatment Trimethoprim-sulfamethoxazole (TMP-SMZ) has proven effective in treating cyclospora infection. Dose- A combination of 160 mg TMP & 800 mg of SMZ 3 times/week. Oral rehydration as a supportive treatment.