Malaria: Clinical and Epidemiological Aspects

The cycle of invasion, multiplication, and reinvasion takes place over 48 hours for P. falciparum, P. vivax, and P. ovale; 72 hours for P. malariae; and 24 hours for P. knowlesi. Although some degree of anemia resulting from hemolysis of infected red blood cells is an expected consequence of symptomatic malaria infections, the pathogenesis of severe malarial anemia, seen most commonly in P. falciparum disease, and also present withP. vivax, is multifactorial. Malaria during pregnancy also carries a risk of adverse birth outcomes such as spontaneous abortion, stillbirth, and premature birth or intrauterine growth restriction, both of which contribute to low birth weight, which is the single most important indicator of infant mortality. With the recent call for malaria elimination, more tools, including vaccines, can be anticipated in the near future. Host genetic factors that play important roles in malaria risk and epidemiology are summarized in this chapter. The new goal of using vaccines for malaria elimination places an increased emphasis on vaccines that would completely prevent infection and thus transmission by targeting the pre-erythrocytic stages of the parasite life cycle or block transmission directly by generating immunity against the sexual and mosquito stages. Most malaria vaccines are based on recombinant versions of antigenic targets from specific stages of the parasite life cycle, although DNA vaccines and viral vector expression approaches have been used with limited success to date. The most advanced malaria vaccine is based on the circum sporozoite protein that coats the surface of the infectious sporozoites.