A Critique of Merozoite and Sporozoite Vaccines in Malaria

Abstract

How can a vaccine be effective against an organism that in nature is poorly immunogenic? Children within hyperendemic areas are repeatedly infected with Plasmodium falciparum malaria over many years before the incidence of parasitemia, splenomegaly, and clinical disease decreases. This immunity, once acquired, may wane in the absence of repeated exposure to malaria. The theoretical problems of a malaria vaccine are further complicated by antigenic differences that exist between the different geographic strains of P. falciparum. James et al. (1932) observed that a patient who was resistant to challenge with the Indian strain of P. falciparum was susceptible to the Sardinian strain. On the other hand, gamma globulin from immune, adult West Africians suppressed falciparum parasitemia in East African children (McGregor et al. 1963). In addition, antigenic differences do not appear to exist between sporozoites of falciparum strains isolated from Asia and Panama; individuals who were immunized by irradiated sporozoites from one area of the world resisted challenge by sporozoites from other areas (Clyde et al. 1973).