Genetic Basis of Host Infectivity by Cryptosporidium

PROJECT SUMMARY/ABSTRACT Cryptosporidium is a wide-spread enteric pathogen that causes severe diarrheal disease in immunocompromised patients and infants, especially in the developing world. There are more than 20 described species of Cryptosporidium some of which show narrow host ranges while others are quite broad. C. parvum has a relatively broad host range infecting many agricultural animals and causing zoonotic infections in humans. C. parvum is further divided into subtypes that undergo recombination in the wild often resulting in in differences in host range, infectivity, and virulence. The factors that control host range of C. parvum as well as their pathogenicity in different hosts are largely unknown, presenting a major gap in our understanding of this important group of parasites. In preliminary studies, we have defined major virulence differences between common laboratory variants of C. parvum during infection in immunocompromised mice. High-virulence isolates are associated with elevated oocyst shedding and lethality, while low-virulence isolates cause only mild, non-lethal infections. Whole genome sequencing identified numerous single nucleotide polymorphisms in candidate genes that likely control these phenotypic differences. We recently developed a stem-cell derived system for culturing differentiated intestinal enterocytes that allows complete development of C. parvum in vitro, including production of viable oocysts. In preliminary studies, we tagged C. parvum isolates with fluorescent reporters using CRISPR/Cas9 gene editing and used these lines to conduct genetic crosses in vitro. Analysis of the recombinant progeny from crossed lines demonstrates that meiosis results in Mendelian chromosome reassortment. In the proposed studies, we will cross fluorescently tagged virulent isolates with avirulent isolates in vitro, sort recombinant progeny using FACS, and expand them in mice to select for genes associated with increased fitness. The contributing loci will be mapped using Bulk Segregant Analysis to define candidate genes that will be confirmed by CRISPR/Cas editing. These studies should lead to a molecular understanding of pathogenicity of C. pavrum and may identify genes responsible for mediating infectivity and host-range.