Recent studies into the global causes of severe diarrhea in young children have identified the protozoan parasite Cryptosporidium as the second most important diarrheal pathogen after rotavirus1–3. Diarrheal disease is estimated to be responsible for 10.5% of overall child mortality4. Cryptosporidium is also an opportunistic pathogen in the context of HIV-AIDS and organ transplantation5,6. There is no vaccine and only a single approved drug that provides no benefit for those in gravest danger, malnourished children and immunocompromised patients7,8. Cryptosporidiosis drug and vaccine development is limited by the poor tractability of the parasite, which includes lack of continuous culture, facile animal models, and molecular genetic tools3,9. Here we describe an experimental framework to genetically modify this important human pathogen. We establish and optimize transfection of C. parvum sporozoites in tissue culture. To isolate stable transgenics we develop a mouse model that delivers sporozoites directly into the intestine, a Cryptosporidium CRISPR/Cas9 system, and in vivo selection for aminoglycoside resistance. We derive reporter parasites suitable for in vitro and in vivo drug screening, and we evaluate the basis of drug susceptibility by gene knock out. We anticipate the ability to genetically engineer the parasite will be transformative for Cryptosporidium research. Genetic reporters will provide quantitative correlates for disease, cure and protection and the role of parasite genes in these processes is now open to rigorous investigation.

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The apicomplexan parasite Cryptosporidium is a leading cause of diarrheal disease and an important contributor to overall global child mortality. We currently lack effective treatment and immune prophylaxis. Recent advances now permit genetic modification of this important pathogen. We expect this to produce rapid advances in fundamental as well as translational research on cryptosporidiosis. Here we outline genetic engineering for Cryptosporidium in sufficient detail to establish this technology in any laboratory that requires access to this key technology. This chapter details the conceptual design consideration, as well as all the experimental steps required to transfect, select, and isolate transgenic parasites. We also provide detail on key in vitro and in vivo assays to detect, validate, and quantify genetically modified Cryptosporidium parasites.

SUMMARY Ethanolamine glycerophospholipids are ubiquitous cell membrane components. Trypanosomatid parasites of the genus Leishmania synthesize the majority of their ethanolamine glycerophospholipids as 1-O-alk-1′-enyl-2-acyl-sn-glycero-3-phosphoethanolamine or plasmenylethanolamine (PME) through the Kennedy pathway. PME is a subtype of ether phospholipids also known as ethanolamine plasmalogen whose functions are not well characterized. In this study, we investigated the role of PME synthesis in Leishmania major through the characterization of an ethanolamine phosphotransferase (EPT) mutant. EPT-null parasites are largely devoid of PME and fully viable in regular medium but fail to proliferate in the absence of fetal bovine serum. They exhibit significant abnormalities in the synthesis and localization of GPI-anchored surface molecules. EPT-null mutants also show attenuated virulence in BALB/c mice. Furthermore, in addition to PME synthesis, ethanolamine also contributes to the production of phosphatidylcholine, the most abundant class of lipids in Leishmania. Together, these findings suggest that ethanolamine production is likely required for Leishmania promastigotes to generate bulk phospholipids, to handle stress, and to control the expression of membrane bound virulence factors.