ABSTRACT
The causative organisms of the disease malaria are protozoa of the genus Plasmodium, family Plasmodiidae, suborder Haemosporidiidae, order Coccidia. The 120 or so species of Plasmodium are found in the blood of mammals, reptiles and birds, and are recognized taxonomically by the presence of two types of asexual division: schizogony, in the vertebrate host; and sporogony, in the insect vector. Within the vertebrate host, schizogony is found both within erythrocytes (erythrocytic schizogony) and in other tissues (exo-erythrocytic schizogony). The great majority of malarial parasites are transmitted by mosquitoes, and the parasites of humans are exclusively transmitted by anophelines. Importantly, the parasites of humans are of two subgenera, Laverania and Plasmodium. The former subgenus includes P. falciparum, the most pathogenic form of malaria, and the closely related P. reichenowi, a parasite of the higher primates. The latter subgenus includes the remaining parasites of humans, namely P. vivax, P. malariae and P. ovale. Parasites of the other mammals also fall into two subgenera: Plasmodium and Vinckeia; the latter includes the parasites of lemurs and lower mammals. Parasites of birds and reptiles are of the subgenus Plasmodium and it is to this ancestral group of parasites that the subgenus Laverania may be most closely related (Table 2.1). Three malaria parasites are found exclusively in humans: P. falciparum (Welch, 1897), P. vivax (Grassi and Feletti, 1890) and P. ovale (Stephens, 1922). P. malariae (Laveran, 1881) is found in both humans and African apes, and the parasite P. brazilianum is probably the same species found in South American monkeys. The diseases caused by the four human parasites have, in the past, been described as follows:
P. vivax: benign tertian, simple tertian, tertian
P. malariae: quartan
P. falciparum: malignant tertian (MT), subtertian, aestivo-autumnal, tropical, pernicious
P. ovale: ovale tertian.
