Parasitic protozoa and helminths: biological and immunological challenges

Parasitic protozoans and helminths pose considerable medical as well as scientific challenges. Investigations of the complex and very different life cycles of these organisms, their adaptation to the obligate parasitic mode of life, and their ability to face the hostile host environment have resulted in many exciting discoveries. Invasion of host erythrocytes by plasmodial sporozoites and intact skin by schistosomal cercariae are outlined as examples of the elaborate mechanisms of parasitism. Isolation and characterization of single protective antigens or subunit vaccines from these two organisms are examined as models for vaccine development. Finally, developments in exploring gene regulation in protozoans and free and parasitic nematodes are briefly outlined.