Vaccines against tropical parasitic diseases: a persisting answer to a persisting problem.

Live and live-attenuated whole organism vaccines against Plasmodium falciparum malaria and cutaneous leishmaniasis due to Leishmania major remain the most uniformly effective vaccines against human parasitic diseases. These vaccines are discussed in terms of the nature of the T cell populations that mediate the strong and durable localized immunity to these infections, and the requirement for persisting antigen to generate and maintain the protective response. The difficulties in developing subunit vaccines that fulfill this requirement argue that despite their own formidable problems in manufacture and delivery, live and live- attenuated whole organism vaccines against human parasitic diseases should be vigorously pursued.