PLASMODIUM OVALE: CHARACTERISTICS, MORPHOLOGY, LIFE CYCLE - BIOLOGY - 2025

Plasmodium ovale is a species of unicellular protist that constitutes one of the best-known parasites in man, causing a disease that has always wreaked havoc on humanity, malaria.

It was the last of the malaria-causing parasites to be described. This was in the year 1922 by Stephens, who observed it years earlier in the blood of an East African patient. What caught his attention was the oval shape that erythrocytes take, which is why he decided to name it Plasmodium ovale.

Plasmodium ovale in blood. Source: By Dr Osaro Erhabor, from Wikimedia Commons

Plasmodium ovale is perhaps the least dangerous of the Plasmodium genus parasites. Even so, it is capable of generating the development of malaria in healthy individuals, although it is less virulent than the other Plasmodium species.

Taxonomy

Domain: Eukarya

Kingdom: Protista

Phylum: Apicomplexa

Class: Aconoidasida

Order: Haemosporida

Family: Plasmodiidae

Genus: Plasmodium

Species: Plasmodium ovale

Morphology

Plasmodium ovale has various stages when found in the bloodstream. Each stadium has its own characteristics:

Trophozoite

The young has a pigment that forms small dark brown masses. Likewise, it is shaped like a ring that occupies approximately one third of the size of the red blood cell. The cytoplasm forms a circle around the vacuole.

The mature trophozoite is compact, generally does not have a vacuole, and has pigments like the young trophozoite.

Schizont

They occupy more than half of the cytoplasm of the erythrocyte. The pigment is concentrated in a mass.

Gametocyte

Two types of gametocytes are present: macromgametocyte and microgametocyte.

Macrogametocyte

They have condensed chromatin. It can be oval or rounded. It has a light brown pigment diffused throughout the cytoplasm. This is homogeneous.

Microgametocyte

Maintains the shape of the macrogametocyte. The cytoplasm is a colorless or pale halo. The pigment is distributed in small granules. It has dispersed chromatin.

General characteristics

Plasmodium ovale is a protozoan that is responsible for a small percentage of malaria cases in the world.

It is a unicellular eukaryotic organism, which implies that they are made up of a single cell and that within it there is a cell nucleus, in which nucleic acids (DNA and RNA) are contained.

It is parasitic in life, which means that in order to develop fully, it must be within the cells of a host. In this case, the host can be human or some other vertebrate.

Similarly, they require a vector agent, within which the sexual phase of their cycle occurs. The vector of Plasmodium ovale is the female of the genus Anopheles, a type of mosquito.

When it comes to habitat, it is limited. The Plasmodium ovale species is found only in West Africa and some Asian countries such as the Philippines and Indonesia. It is also common in Papua New Guinea.

-Transmission

Malaria is transmitted through the bite of the female mosquito of the genus Anopheles, which can carry the sporocytes in its salivary glands, in such a way that by biting a healthy person, it would be inoculating them.

Malaria is a disease that is highly widespread throughout the world, especially in developing countries. Among the areas most affected by this pathology are the African continent (specifically the sub-Saharan region), Asia and Latin America.

The main risk groups for this disease include:

• People with a weakened immune system, especially those who are infected by the Acquired Immune Deficiency Virus (HIV).
• People who travel to places where the disease is endemic, such as some regions of Africa, Latin America and Asia.
• Emigrants from endemic areas living in non-endemic areas, when they return to their countries of origin.

-Incubation period

The incubation period is the time it takes for the disease to physically manifest itself from the moment the parasite enters the bloodstream.

In the case of Plasmodium ovale, the incubation period is between 12 to 18 days. Of course, there are factors that determine how quickly symptoms will manifest, with the host's immune system conditions having the most influence.

-Signs and symptoms

Malaria is characterized by repetitive attacks in which the following symptoms can be seen:

• High fever
• Heavy sweating
• Chills with tremors that can become intense.
• Diarrhea
• Vomiting
• Severe headache
• Bone pain

-Diagnosis

It is recommended that when a person begins to manifest symptoms that can be credited to malaria, it is to go immediately to the doctor so that he can start the process of making an accurate diagnosis.

There are several tests that can be applied to diagnose this pathology.

Peripheral blood smear and thick blood film

For the first, a drop of blood is placed on a slide, to be later spread with the help of another slide, forming a thin layer.

In the thick drop, several drops are placed on a slide, which coalesce and spread, forming a thick, uniform layer. These samples are then observed under a microscope to detect the presence of the parasite.

Blood stains

For the diagnosis of this pathology, there are many stains that can be used, such as: Giemsa, Field, Leishman stain and acridine orange stain.

Detection of parasitic antigens

They are commercial rapid tests that seek to detect specific proteins that synthesize the various species of Plasmodium. These include the histidine-rich protein 2 (HRP-2) produced by Plasmodium falciparum and the parasitic lactate dehydrogenase (LDH) secreted by the 4 species of

Polymerase Chain Reaction Test (PCR)

It is a molecular diagnostic technique that detects the DNA of any of the Plasmodium species that cause malaria.

-Treatment

Treatment for malaria is varied. It will always depend on the judgment of the treating physician.

Among the drugs used are chloroquine and primaquine, as well as quinine. These drugs have been shown to be effective in the eradication of parasitic forms.

References

1. Collins, W. and Jeffery, G. (2005). Plasmodium ovale: Parasite and Disease. Clinical Microbiology Reviews. 18 (3). 570-581.
2. . Fairley, NM (1933). A case of malaria due to Plasmodium ovale Stephens 1922. Med. J. July 15: 1-4.
3. Laboratory Identification of Parasites of Public Health Concern. Plasmodium ovale. Retrieved from: cdc.gov
4. R López-Vélez. Reviews and Updates: Infectious Diseases: Malaria. Medicine. Volume 08 - Number 70 p. 3742 - 3750
5. Worrall, E., Basu, S. and Hanson, K. (2005) “Is malaria a disease of poverty? A review of the literature, ”Tropical Med and Intl Health 10: 1047-1059.