Infectivity and Virulence of Cryptosporidium Non-parvum Species in Healthy Adult VolunteersEPA Grant Number: R829180
Title: Infectivity and Virulence of Cryptosporidium Non-parvum Species in Healthy Adult Volunteers
Investigators: Chappell, Cynthia L. , DuPont, Herbert L. , Janecki, A. , Okhuysen, Pablo C. , Tzipori, Saul , Widmer, Giovanni
Current Investigators: Chappell, Cynthia L. , Okhuysen, Pablo C. , Tzipori, Saul , Widmer, Giovanni
Institution: The University of Texas at Houston , St. Luke's Episcopal Hospital , The University of Texas Medical School , Tufts University
Current Institution: The University of Texas at Houston
EPA Project Officer: Page, Angela
Project Period: September 1, 2001 through August 31, 2004 (Extended to August 31, 2005)
Project Amount: $524,540
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Cryptosporidiosis in humans was thought to be associated with C. parvum only, but recent evidence suggests other Cryptosporidium species can infect/cause illness in immunocompromised individuals. C. meleagridis, C. felis, and C. muris have been detected in immunocompromised and immunocompetent humans. These observations raise questions about the role of non-parvum species in community diarrheal illness.
Previous experimental infections in healthy volunteers have used C. parvum genotype 2 isolates; further studies of genotype 1 isolates are in progress. Development of the gnotobiotic (GNB) pig model provides a lab host for the amplification of C. parvum genotype 1 isolates. Results suggest the GNB pig will support the replication of other Cryptosporidium species as well. This advance in identifying a human surrogate makes amplification of non-parvum isolates for use in volunteer studies possible.
Experimental cryptosporidiosis in healthy adults has revealed variability in infectivity, outcome, and immune response to geographically-diverse genotype 2/C isolates. Recent in vitro studies, using a human enterocyte cell line, HCT-8, show that the percent infectivity of the 3 isolates studied in vitro correlates highly with human ID50's, suggesting that this model may serve as an in vitro surrogate to human infections and could be valuable in assessing environmental oocysts for their human disease potential.
It is hypothesized that non-parvum species of Cryptosporidium can replicate and cause illness in immunocompromised individuals; thus, persons with normal immune systems will also be susceptible to infection and illness with these isolates.
The study can be divided into 3 parts: (1) establishment of the Cryptosporidium species (C. felis, C. muris, C. meleagridis or C. baileyi) in lab host(s) and confirmation of genotypic stability, (2) examination of the infectivity and development of the Cryptosporidium species, and (3) determination of the infectivity and host response in healthy volunteers challenged.
The first objective will be accomplished by passaging the oocysts in GNB pigs or avian species as required. Genotypic analysis will be based on multilocus polymorphism, and genetic stability after passage in animal and human hosts will be followed by specific species biomarkers. Human enterocyte cell cultures will be used to study infectivity and parasite development (all Cryptosporidium species). Likewise, infectivity and illness in humans will be studied by challenging healthy adult volunteers with 105 oocysts per subject employing a protocol that has been described in previously published work.
Documenting infectivity and illness outcomes of humans challenged with non-parvum species will significantly advance the understanding of community acquired cryptosporidiosis and allow the development of more accurate risk assessment models. Antibody and cellular studies in humans will examine the immune response to exposure and/or infection. Fecal samples will be screened for mucosal antibody, which (if found) will be examined for cross-reactivity among antigens from various C. parvum species. These studies will be important in understanding Cryptosporidium infection in the community and will have significant implications for water quality regulations.