Plasmodium malariae malaria occurs with a much lower incidence than P. vivax and P. falciparum. Only 4% of malarial disease is due to Plasmodium malariae.
Disease / Pathogenesis
Plasmodium malariae malaria disease is milder than P. vivax and P. falciparum but can cause a chronic life long infection. Plasmodium malariae causes paroxysms that are quartan (paroxysms that typically recur every 72 hours or every forth day, reckoning the day of the paroxysm as the first). It is initiated by the synchronous rupture of erythrocytes with the release of new infectious blood stages forms know as merozoites. Toxic byproducts of the process and loss of red blood cells cause fevers, and can lead to chronic nephrotic syndrome. More complications of malaria can also be impairment of consciousness, neurological abnormalities, hypoglycemia and low blood pressures caused by cardiovascular collapse. Once there is an establishment of chronic nephrotic syndrome, treatment options are limited as there is poor treatment response and subsequently high rates of mortality occur with the syndrome.
Location in the Host
Plasmodium malariae location is the blood and unlike P. vivax and P. ovale, there are no dormant hypnozoites (latent hepatic sporozoites) within the liver for later inactivation. The schizonts have 6-12 merozoites present, with the average being 8.
Plasmodium malariae has a very large geographical distribution that includes Africa, Asia, and South America. But it accounts for about 4% of reported malarial infections. P. vivax accounts for the most malarial infections at 44%, P. falciparum at 43%, and P. ovale at 3%. Another 6% are undetermined.
The Plasmodium malariae life cycle is similar to most malarial parasites. The development of hypnozoites is however not a characteristic of Plasmodium malariae as is seen in P. vivax and P. ovale where relapses occur. There is recurrence of disease in Plasmodium malariae which arise from increased numbers of persisting blood stage forms to clinically detectable levels, not from the presence of persisting liver stage forms, hypnozoites. The Plasmodium malariae produces a quartan cycle or periodicity of 73 hours … whereas the other malaria such as P. vivax and P. ovale produce a tertian cycle or periodicity of every 48 hours. P. falciparum is also considered tertian but can vary somewhat due to the infectivity of red bloods cells including all stages.
Below is a CDC depiction of the life of the Plasmodium spp..
Morphology & Diagnosis
Plasmodium malariae infects older red blood cells and therefore you will not see the enlarged cells seen with P. vivax and P. ovale. Trophozoites within the red blood cells are frequently described as compact with a dense cytoplasm and having a “band” shape that crosses through a large portion of the center of the red blood cell. They can also take on a “basket” like shape. Both examples of characteristic trophozoites are shown in the image below. Ziemann dots are rarely seen. The pigment of the parasite is dark brown, coarse and conspicuous. The schizonts will have between 6-12 merozoites with an average of 8.