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CRYPTOSPORIDIUM HOMINIS: EXPERIMENTAL CHALLENGE OF HEALTHY ADULTS

Cryptosporidium hominis causes diarrhea in humans and has been associated with community outbreaks. This study describes the infectivity, illness, and serologic response after experimental challenge of 21 healthy adult volunteers with 10–500 C. hominis (TU502) oocysts. Sixteen subjects (76.2%) had evidence of infection; the 50% infectious dose (ID₅₀) was estimated to be 10–83 oocysts using clinical and microbiologic definitions of infection, respectively. Diarrhea occurred in 40% of subjects receiving 10 oocysts with a stepwise increase to 75% in those receiving 500 oocysts. A serum IgG response was seen in those receiving more than 30 oocysts. Greatest responses were seen in volunteers with diarrhea and oocyst shedding. Volunteers with no evidence of infection had indeterminant or negative IgG responses. Cryptosporidium hominis10 oocysts) and is clinically is infectious for healthy adults (ID₅₀ = similar to C. parvum-induced illness. In contrast to C. parvum, C. hominis elicted a serum IgG response in most infected persons.

Received May 23, 2006. Accepted for publication July 1, 2006.

Acknowledgments: We express our gratitude to the many individuals who contributed to these studies: the participating volunteers; Nai-Hui Chiu, Madeline Ottosen, and the research nursing staff at the University Clinical Research Center for their expertise and attention to the many details of the study; and to Philip Lupo, Audrey Wanger, and Zhi Dong Jiang for excellent technical assistance. Data from this study, in part, have been presented at the annual meeting of the American Society of Parasitologists. August 1–5, 2003, Halifax, Nova Scotia and the American Society of Tropical Medicine and Hygiene, November 7–11, 2004, Miami, Florida, Abstract no. 35.

Financial support: This study was supported, in part, by the National Center for Environmental Research STAR Program of the Environmental Protection Agency (grant no. GR828035-01-0 to Cynthia L. Chappell), the National Institutes of Health General Clinical Research Centers (grant no. RR-02558), and the National Institute of Allergy and Infectious Diseases, (grant no. AI52781 to Giovanni Widmer and grant no. NO1-AI-25466 to Saul Tzipori).

^* Address correspondence to Cynthia L. Chappell, The University of Texas–Houston School of Public Health, 1200 Herman Pressler Street, Suite 118A, Houston, TX 77030. E-mail: Cynthia.L.Chappell{at}uth.tmc.edu

Authors’ addresses: Cynthia L. Chappell, University of Texas-Houston School of Public Health, 1200 Herman Pressler Street, Suite 118A Houston, TX 77030, Telephone: 713-500-9026, Fax: 713-500-9020, E-mail: Cynthia.L.Chappell{at}uth.tmc.edu. Pablo C. Okhuysen, Division of Infectious Diseases, University of Texas Medical School, 6431 Fannin, Room 2.112, Houston, TX 77030, E-mail: Pablo.C.Okhuysen{at}uth.tmc.edu. Rebecca Langer-Curry, Office of Environmental Safety, Baylor College of Medicine, Room K104, 1 Baylor Plaza, Houston, TX 77030, E-mail: langercu{at}bcm.tmc.edu. Giovanni Widmer, Donna E. Akiyoshi, Sultan Tanriverdi, and Saul Tzipori, Division of Infectious Diseases, Tufts Cummings School of Veterinary Medicine, North Grafton, MA 01536, E-mails: giovanni.widmer{at}tufts.edu, donna.akiyoshi{at}tufts.edu, sultan.tanriverdi{at}tufts.edu, and saul.tzipori{at}tufts.edu.