Plasmodium malariae and Plasmodium ovale--the "bashful" malaria parasites

Abstract

Although Plasmodium malariae was first described as an infectious disease of humans by Golgi in 1886 and Plasmodium ovale identified by Stevens in 1922, there are still large gaps in our knowledge of the importance of these infections as causes of malaria in different parts of the world. They have traditionally been thought of as mild illnesses that are caused by rare and, in case of P. ovale, short-lived parasites. However, recent advances in sensitive PCR diagnosis are causing a re-evaluation of this assumption. Low-level infection seems to be common across malaria-endemic areas, often as complex mixed infections. The potential interactions of P. malariae and P. ovale with Plasmodium falciparum and Plasmodium vivax might explain some basic questions of malaria epidemiology, and understanding these interactions could have an important influence on the deployment of interventions such as malaria vaccines.

Figure 1

Age-specific prevalence of Plasmodium infections. (a) Plasmodium falciparum (red) and Plasmodium vivax (blue) infections. (b) Plasmodium malariae (brown) and Plasmodium ovale (green) infections. (c) Mixed infections: concurrent infection with more than one Plasmodium species. Infections were detected by light microscopy (broken line) and LDR–FMA assay (unbroken line) in 1182 paired samples from Wosera, PNG [29].