Molecular genetic strategies in Toxoplasma gondii: close in on a successful invader

Toxoplasma gondii is an obligate intracellular parasite with an exceptional ability to invade, survive and replicate within nearly all nucleated cells. Upon differentiation into an encysted form (bradyzoites), the parasites escape the host immune defenses and thus persist long enough in man and other hosts to ensure maintenance of transmission. This protozoan parasite has long been known to cause severe congenital infections in humans and animals but has recently gained additional notoriety as an opportunistic pathogen associated with AIDS. Development of a DNA transfection system for T. gondii has provided a new tool for exploring molecular aspects of important processes such as invasion and differentiation. Additional strategies associated with genetic transformation have been devised and elaboration of even more desirable molecular tools is in progress.