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2. 2 Cryptosporidium Volunteer Study Investigators: Cynthia Chappell, PhD Pablo Okhuysen, MD Herbert DuPont, MD Isolates: Charles Sterling, PhD (Iowa) Karen Snowden, DVM (TAMU) Joseph Crabb, PhD (UCP) Laboratory staff: Blue Johnson Han Dang Constance Wang Michael Coletta Sonia Baker Danny Nguyen Marilyn Marshall UCRC Nursing staff: Madeline Jewell, RN Julie Rice, RN Nai-Hui Chiu, RN

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6. 6 Preparation of Challenge Dose Passaged in calf and purified Shipped to Houston in potassium dichromate Tested for adventitious agents (viruses, bacteria) Adjusted for appropriate number Delivered via gelatin capsule

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11. 11 Ref of method: Reed and Muench, Am J Hyg 27:493, 1938 ID 50 in Antibody-negative Volunteers

12. 12 Clinical Outcome in Volunteers

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15. 15 Dose Response Curves in Neonatal Mice

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17. 17 Cryptosporidium Infection in HCT-8 Cells

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19. 19 Infectivity in Human vs Neonatal Mice and HCT-8 Cells r 2 = 0.933r 2 = 0.548

20. 20 Conclusions  C. parvum oocysts vary widely in infectivity, even within the same genotype  HCT-8, a human enterocyte cell line, shows a higher correlation with human genotype 2 infectivity than does the neonatal mouse model.  HCT-8 also has the advantage of supporting genotype 1 replication.