Osmiophilic bodies and the odd organelles of alveolates.

The apicomplexa are parasitic protozoa that are responsible for important human and animal diseases, including malaria, toxoplasmosis, cryptosporidiosis, coccidiosis and babesiosis. Like other members of the superphylum Alveolata, apicomplexans have regulated exocytosis of specialized secretory organelles, such as the apicomplexan-specific rhoptries and micronemes that are required for host cell invasion. The secretions of another class of organelles, the dense granules and osmiophilic bodies, are proposed to be required for maintenance of the parasitophorous vacuole and host cell egress. Little is known about the osmiophilic bodies and to date only one protein, P377, has been localized to this organelle. In this issue, de Koning-Ward et al. describe the disruption of pfg377 in the virulent human malaria parasite, Plasmodium falciparum, which results in reduced osmiophilic body formation, a marked decrease in female fitness, and dramatically impaired infectivity to mosquitoes. These findings suggest that targeting PFG377 may be a strategy to block parasite transmission.