Plasmodium malariae - Introduction, Classification, History, Habitat, Morphology, Culture

Introduction of Plasmodium malariae

The genus Plasmodium causes the vector-borne disease malaria. These parasites show an alternation of generation accompanied by an alternation of hosts. In the human host, the asexual cycle (schizogony) takes place inside the erythrocytes while the sexual cycle (sporogony) takes place in the mosquito host.

Typically, the infected erythrocytes produce pigments that are visualized by light microscopy.

Plasmodium vivax, P. ovale, and P. malariae belong to the subgenera Plasmodium while P. falciparum belongs to the subgenus Laverania.

Plasmodium malariae is the causative agent malariae malaria or quartan malaria.

Classification of Plasmodium malariae

Kingdom: Chromista

Subkingdom: Harosa

Infrakingdom: Halvaria

Superphylum: Alveolata

Phylum: Apicomplexa

Class: Aconoidasida

Order: Haemospororida

Family: Plasmodiidae

Genus: Plasmodium

Species: P. malariae

History of Plasmodium malariae

Plasmodium malariae is the parasite of chimpanzees and was previously named Plasmodium rodhaini.

Habitat of Plasmodium malariae

In the mammal host, Plasmodium malariae infects only old erythrocytes.

Morphology of Plasmodium malariae

The various morphological forms of Plasmodium malariae depend on the host the parasite is residing in i.e. the diagnostic form or the infective form.

Diagnostic forms in humans

The diagnostic forms of Plasmodium malariae found in the human host include

• Early trophozoite (ring form)

• Late trophozoite (trophozoite form)

• Schizont

• Gametocytes

Early trophozoite (ring form)

• are relatively large and occur in peripheral blood

• have a delicate blue-stained ring of cytoplasm with a red chromatin dot

• in some cases, two red chromatin dots can be found separated or closed together

• sometimes, two early trophozoites can be found in a single infected RBC

• the cytoplasm of Plasmodium malariae stains deep blue than P. vivax

• also, the cytoplasm of Plasmodium malariae is smaller, thicker, and heavier than that of P. vivax

Late trophozoite (trophozoite form)

• are large but lack amoeboid form

• smaller than P. vivax

• consists of abundant chromatin, yellow-brown coarse pigment granules, and an inconspicuous vacuole which is characteristic

• show characteristic band form (ribbon-like) and stretch directly across the infected erythrocytes

Schizont

• young schizonts are small and compact with few chromatin masses and coarse pigments

• mature schizont contains around 6 to 12 merozoites

• merozoites are arranged typically in the form of ‘rosettes’ or ‘daisy-head’ pattern

• found in peripheral blood

• mature schizonts almost fill their host cells

Gametocytes

There are two types of gametocytes- macrogametocytes, and microgametocytes. Immature gametocytes are found in the peripheral blood.

Macrogametocytes

• smaller than P. vivax

• they are round or oval, compact, and filled with enlarged erythrocytes

• smaller nucleus with a compact mass of chromatin

• the fine granules are arranged in small masses and occur near the periphery of P. vivax

• the cytoplasm stains blue while chromatin pigments deep red and violet

Microgametocytes

• smaller than macrogametocytes

• oval or round with a large nucleus

• chromatin granules are arranged to form a spindle

• cytoplasm, which is dark blue, contains dark, coarse hemozoin pigments distributed throughout the cytoplasm

• do not occupy the entire host RBC

Infective form

The infective form of Plasmodium malariae for humans is the sporozoites.

Sporozoites

• measures 13μm to 14μm

• thicker and coarser than other Plasmodium species infecting man

Culture of Plasmodium malariae

The culture of Plasmodium malariae is still in the experimental stage. Studies have been conducted to culture Plasmodium malariae in mixed culture with P. falciparum.