Apicomplexa are an extremely diverse group of unicellular organisms that infect humans and other animals.Despite the great advances in combating infectious diseases over the past century,these parasites still have a tremendous social and economic burden on human societies,particularly in tropical and subtropical regions of the world.Proteases from apicomplexa have been characterized at the molecular and cellular levels,and central roles have been proposed for proteases in diverse processes.In this work,16 new genes encoding for trypsin proteases are identified in 8 apicomplexan genomes by a genome-wide survey.Phylogenetic analysis suggests that these genes were gained through both intracellular gene transfer and vertical gene transfer.Identification,characterization and understanding of the evolutionary origin of protease-mediated processes are crucial to increase the knowledge and improve the strategies for the development of novel chemotherapeutic agents and vaccines.