Abstract: The present invention is directed to a novel B. microti-based promoter and expression system. The present invention is also directed to a novel method of transfecting B. microti by electroporation, the resulting transfected B. microti parasite cell lines, and optionally, B. microti transfected with a particular novel promoter. In some embodiments, transgenic B. microti parasites that express reporter genes and their uses are provided. In certain embodiments, a multi-functional promoter controls multiple genes, e.g. a bifunctional promoter may control a gene of interest and a reporter or selection gene. The promoter may be particularly useful to control expression of apicomplexan genes and form apicomplexan proteins, e.g., without limitation, those of Babesia parasites. In embodiments, expression systems comprising the promoter are provided. In certain embodiments, B. microti-based systems that express reporter genes are provided.