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World Malaria Day: An Overview of Malaria Disease

(Source: Centers for Disease Control and Prevention)

Malaria is an infectious disease caused by a parasite, the protozoan genus Plasmodium, and is usually transmitted through mosquito bites, particularly from female Anopheles mosquitoes. Only female Anopheles mosquitoes can cause malaria because females can bite and suck blood to obtain nutrients and protein for their eggs, while males cannot. When a mosquito infected with this parasite bites a human, the parasite will enter the human body and settle in the liver before attacking the red blood cells and causing clinical symptoms. Clinical symptoms that may occur are fever, chills, nausea, vomiting, headache, anemia, and an enlarged spleen. There are five types of malaria parasites in the world that can infect human red blood cells, namely:

1. Plasmodium falciparum

It causes falciparum or tropical malaria, the most severe type of malaria and the only one that causes microvascular disease and various severe complications, such as cerebral malaria, severe anemia, acute renal failure, shortness of breath, and others.

2. Plasmodium vivax

It can cause tertian malaria, which, without treatment, resolves on its own within 2 – 3 months. However, there is a 50% chance of relapse within a few weeks to 5 years after the initial illness.

3. Plasmodium malariae

It causes asymptomatic quartan malaria for a long time.

4. Plasmodium ovale

It causes malaria ovale or mild tertian. This type is commonly found in Africa and the Western Pacific with milder symptoms and often resolves without treatment.

5. Plasmodium knowlesi

Found in Southeast Asia as a natural pathogen of long-tailed and pig-tailed macaques. However, P. knowlesi is now zoonotic and infects humans. This species has a 24-hour replicative cycle, so it can quickly develop into a severe infection.

(Source: Centers for Disease Control and Prevention)

The life cycle of Plasmodium sp. consists of two stages, namely the asexual cycle (schizogony) that occurs in humans and the sexual cycle (sporogony) that arises in mosquitoes. The following explains the life cycle of malaria parasites in humans and mosquitoes.

  • Initial replication in the liver (exo-erythrocytic, letter A):

1. A female Anopheles mosquito infected with malaria inoculates sporozoites in the mosquito’s salivary glands into the human host

2. Sporozoites begin to infect liver cells

3. Sporozoites mature into schizonts

4. The schizont ruptures and releases merozoites (for P. vivax and P. ovale, in this cycle, some parasites present in liver cells do not continue their process to erythrocyte cells or enter a dormant phase and are embedded in liver tissue called hypnozoite)

  • Asexual multiplication in erythrocytes (erythrocytic schizogony, letter B):

5. Merozoites infect red blood cells

6. The ring stage trophozoites mature into schizonts and rupture, releasing merozoites

7. Some parasites differentiate into the sexual erythrocytic stage (gametocytes)

  • Multiplication of parasites in mosquitoes (sporogonic cycle, letter C):

8. Male gametocytes (microgametocytes) and female gametocytes (macro gametocytes enter the mosquito’s body during mosquito blood sucking

9. Microgametes penetrate macrogametes to produce a zygote

10. The zygote turns motile and elongated (ookinete)

11. Ookinetes invade the mosquito midgut wall and develop into oocysts

12. Oocysts grow, rupture, and release sporozoites into the mosquito’s salivary glands

Until now, malaria has been treated with the use of antimalarial drugs. Antimalarial drugs are divided into several types based on the activity of the drug at the parasite stage as follows:

  • Tissue schizonticides for causal prophylaxis

The drugs included in this type are primaquine and pyrimethamine. This type of drug acts early in the erythrocytic cycle after developing in the liver.

  • Tissue schizonticides to prevent relapse.

The primary drug of this type is primaquine, but pyrimethamine also has similar activity. These drugs act on hypnozoites of P. vivax and P. ovale in the liver and are used as anti-relapse drugs.

  • Blood schizonticides

Drugs that fall under this type are quinine, chloroquine, mefloquine, halofantrine, sulfadoxine, and pyrimethamine. These types of drugs kill the parasites during the erythrocytic cycle.

  • Gametocytosides

These include primaquine for all four Plasmodium species and chloroquine and quinine for P. vivax, P. malariae, and P. ovale. These drugs destroy the sexual forms of all Plasmodium species in the blood, thus preventing parasite transmission to mosquitoes.

  • Sporontocides

The drugs included in this type are primaquine and chloroguanide. They work by inhibiting oocyst development in mosquitoes to prevent further transmission.

Malaria can be prevented by avoiding mosquito bites by wearing mosquito nets, spraying the house’s walls with insecticide, keeping the house clean, dry, and hygienic, and preventing stagnant water.

References:

  1. Azlin, E. (2016). Obat anti malaria. Sari Pediatri, 5(4), 150-4.
  2. Centers For Disease Control and Prevention. (2022). Malaria. www.cdc.gov/malaria, accessed April 22, 2023.
  3. Fitriany, Julia and Ahmad Sabiq. (2018). Malaria. Lhokseumawe: Malikussaleh University.

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