Abstract
Cryptosporidium parvum is a major cause of diarrhea and malnutrition in the developing world, and a potential bioterrorism agent. C. parvum contains very streamlined nucleotide biosynthetic pathways. Several genes encoding these enzymes appear to have been obtained by horizontal gene transfer from bacteria and algae, and thus are highly diverged from the host. Such enzymes represent attractive targets for the development of anticryptosporidial drugs. A program of drug discovery exploiting these unexpectedly diverged enzymes has been undertaken. Efforts to develop anticryptosporidial drugs targeting C. parvum IMP dehydrogenase and thymidine kinase are summarized in this chapter.