Abstract: This invention relates uses of Toxoplasma gondii chorismate synthase, a component components of plant-like metabolic pathways not including psbA or PPi phosphofructokinase and not generally operative in animals or encoded by the plastid DNA, in assays to develop compositions that interfere with Apicomplexan growth and survival. Components of the pathways include enzymes, transit peptides and nucleotide sequences encoding the enzymes and peptides, or promoters of these nucleotide sequences to which antibodies, antisense molecules and other inhibitors are directed. Diagnostic and therapeutic reagents and vaccines are developed based on T. gondii chorismate synthase and its inhibitors.