Loss of Stages after Continuous Passage of Toxoplasma gondii and Besnoitia jellisoni*

Abstract
T. gondii, passed from mouse to mouse in the tachyzoite stage for 30-35 generations, developed cysts, which, when fed to cats, failed to produce oocysts. B. jellisoni, passed similarly for 20 generations, lost the capacity to form cysts. These phenomena are explained by a loss of genomes or gene products during the rapid passage selecting for tachyzoites.