The essential host genome for Cryptosporidium survival exposes metabolic dependencies that can be leveraged for treatment.

Cryptosporidium is a leading cause of diarrheal disease, yet little is known regarding the infection cell biology of this intracellular intestinal parasite. To this end, we implemented an arrayed genome-wide CRISPR-Cas9 knockout screen to microscopically analyze multiple phenotypic features of a Cryptosporidium infection following individual host gene ablation. We discovered parasite survival within the host epithelial cell hinges on squalene, an intermediate metabolite in the host cholesterol biosynthesis pathway. A buildup of squalene within intestinal epithelial cells creates a reducing environment, making more reduced glutathione available for parasite uptake. Remarkably, the Cryptosporidium parasite has lost the ability to synthesize glutathione and has become dependent on this host import. This dependency can be leveraged for treatment with the abandoned drug lapaquistat, an inhibitor of host squalene synthase that shifts the redox environment, blocking Cryptosporidium growth in vitro and in vivo.