Chapter 8 : Malaria

Abstract:

Malaria is an ancient disease. The human malaria parasites, Plasmodium falciparum, P. vivax, P. ovale, and P. malariae, are transmitted through the bite of an infected female anopheline mosquito when, during blood feeding, she injects sporozoites from her salivary glands. All of the pathology of malaria is due to parasite multiplication in erythrocytes. The long-term consequences of malaria infections are an enlarged spleen and liver as well as organ dysfunction. Falciparum infections are more severe and, when untreated, can result in a mortality rate of 25% in adults. Falciparum malaria accounts for 50% of all clinical malaria cases and is responsible for 95% of malaria-related deaths. P. vivax and P. ovale malarias also have the capacity to relapse; that is, parasites can reappear in the blood after a period when none were present. Since all of the pathology of malaria is due to parasites multiplying in the blood, most antimalarials are directed at these rapidly dividing stages. Chloroquine and amodiaquine are synthetic antimalarials developed in the 1940s. Regrettably, little is known about the molecular mode of action of many of these drugs or the mechanisms of resistance, although it has been contended that multidrug resistance to halofantrine, mefloquine, chloroquine, and quinine is due to mutations. The vaccines being contemplated are not based on killed or attenuated stages, but, instead, attention is focused on subunit vaccines consisting of selected antigens. The World Health Organization claims that there are over 100 malaria vaccines under development.