Microorganisms in the development of subunit vaccines against parasites.

Because of the increasing problems of resistance to chemicals and chemical residues, preventative vaccination has increasing appeal as a way to control parasite infestations in humans and in animals. Such vaccines are now feasible through the application of genetic engineering technology to allow production of parasite protective antigens in microorganisms in commercially viable quantities at an acceptable cost. This concept is illustrated by describing research toward subunit vaccines against human malaria (P. falciparum) and against the tropical cattle tick (B. microplus). Although the concept is straightforward, difficulties include the identification of a protective antigen, refolding of the initial microbial product to achieve the native conformation, and its formulation to produce a vaccine eliciting an adequate and appropriate immune response.