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Coccidia

Coccidia. characterized by thick-walled oocysts excreted in feces. In Humans Cryptosporidium Isospora Cyclospora Sarcocystis Toxoplasma. GENERAL APICOMPLEXAN LIFE CYCLE. Cryptosporidium parvum. first human case reported in 1976 monoxenous, wide range of animal hosts

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Coccidia

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  1. Coccidia • characterized by thick-walled oocysts excreted in feces • In Humans • Cryptosporidium • Isospora • Cyclospora • Sarcocystis • Toxoplasma

  2. GENERAL APICOMPLEXAN LIFE CYCLE

  3. Cryptosporidium parvum • first human case reported in 1976 • monoxenous, wide range of animal hosts • several host-adapted species? • self-limiting diarrhea in immunocompetent • profuse, watery diarrhea associated with AIDS • life threatening

  4. Extracytoplasmic Location • microvilli extend and fuse to enclose zoite • close association between parasite and host intestinal epithelial cell • called adhesive zone, feeder organelle, etc

  5. Cryptosporidium Life Cycle • Merogony • = schizogony • Gametogony • = gamogony or • = gametocytogenesis • Sporogony • completed in host cell • thin (autoinfection) or thick walled oocysts

  6. Water Borne Outbreaks of Cryptosporidiosis in the USA Modified from Graczyk et al, Parasitol. Today 13:348 (1997)

  7. The Milwaukee Outbreak NEJM 331:161 (1994) • massive cryptosporidiosis outbreak following spring thaw • >400,000 people may have been affected • based on clinical symptoms (acute watery diarrhea) • treated water had high levels of turbidity 3/23-4/5/1993 • oocysts identified in ice made during this period • 100-fold higher prevalence of Cryptosporidium oocysts in stools • other enterics (including Giardia, bacteria, viruses) were at ~normal levels

  8. Factors Favoring Waterborne Cryptosporidiosis • small size of oocysts (4-5 mm) • reduced host specificity and monoxenous development • close associations between human and animal hosts • large number of oocysts excreted (up to 100 billion per calf per day) • low infective dose (<30) • robust oocysts; resistant to chlorine • infectious sporulated oocysts excreted in feces

  9. Human Cryptosporidiosis • associated with epidemic diarrhea in institutions and hospitals • highly transmissible (19% household members)

  10. Molecular Epidemiology Peng et al (1997), Emerg. Inf. Dis. 3:567 • 2 genotypes identified from 39 isolates: • Genotype 1 • only human sources • non-infective for mice or calves • Genotype 2 • human and bovine sources • infective for mice and calves

  11. Two distinct transmission cycles: • anthroponotic (genotype 1) • zoonotic (genotype 2)

  12. Symptoms of 205 patients with Confirmed Cases of Cryptosporidiosis During the Milwaukee Outbreak

  13. Pathogenesis • enterocytes damaged or killed • villus atrophy (blunting) •  Na+ absorption •  permeability • crypt cell hyperplasia •  Cl- secretion • inflammation in lamina propria • cytokines and neurohormones? • enhanced secretion of antibodies (IgA)? • DIARRHEA • enterocyte malfunction (osmotic) • impaired absorption • enhanced secretion • inflammatory diarrhea • mucosal invasion • leukocytes in stools • secretory diarrhea • toxin • watery

  14. Isospora belli • wide geographical distribution (higher prevalence in warmer climates) • monoxenous, probably not zoonosis • invades intestinal epithelial cells • often asymptomatic (seldom reported) • symptoms range from mild gastro-intestinal distress to severe dysentery • often self-limiting, but can become chronic (wasting, anorexia) • symptoms more severe in AIDS patients

  15. Cyclospora cayetanensis • first human case in 1979 • named in 1993 • initially called ‘cyano-bacteria like body’ (CLB) or large Cryptosporidium • related to Eimeria • life cycle unknown • oocysts mature in environment • similar to Isospora? • zoonosis?

  16. Clinical Features • symptoms similar to Cryptosporidium and Isospora • watery diarrhea/frequent stools • 1-2 week duration typical • relapses over 1-2 months • associated with food-borne outbreaks • 37/64 attendees at luncheon near Charleston SC were positive for Cyclospora • raspberries from C. America was source? • oocysts detected on market vegetables in Peru • presumed source: contaminated water or human waste as fertilizer

  17. Intestinal Coccidia • Diagnosis • demonstration of oocysts in feces • acid-fast stain (all three) • autofluorescence (Isospora and Cyclospora) • direct observation (Isospora) • Treatment • paromomycin for Cryptosporidium • modest benefit • lowers parasitemia in AIDS • trimethoprim-sulfamethoxazole for Cyclospora and Isospora

  18. Cryptosporidium • 4-5 mm oocysts • 4 sporozoites • no sporocysts • Cyclospora • 8-10 mm oocyts • 2 sporocysts • 2 sporozoites each • Isospora belli • 30 x 12 mm oocyts • 2 sporocysts • 4 sporozoites each

  19. Cryptosporidium • 4-5 mm oocysts • 4 sporozoites • no sporocysts • Cyclospora • 8-10 mm oocyts • 2 sporocysts • 2 sporozoites each • Isospora belli • 30 x 12 mm oocyts • 2 sporocysts • 4 sporozoites each

  20. Cryptosporidium • 4-5 mm oocysts • 4 sporozoites • no sporocysts • Cyclospora • 8-10 mm oocyts • 2 sporocysts • 2 sporozoites each • Isospora belli • 30 x 12 mm oocyts • 2 sporocysts • 4 sporozoites each

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