Plasmodium Life Cycle: Introduction & Lifecycle of Plasmodium Parasite

The plasmodium life cycle is divided in three main stages: Gametocytes, sporozoites, and merozoites. The plasmodium parasite is called malaria parasite as it is responsible for causing malaria. Plasmodium is an intracellular parasitic protozoan that is transmitted to human beings via the female anopheles mosquito.

• The lifecycle of plasmodium or a malarial parasite starts with feeding on the blood of mammals or any other organism.
• Malaria occurs when the anopheles mosquito bites humans or other mammals thereby injecting plasmodium parasite.
• This parasite is known to infect the erythrocytes or RBC present in mammals, birds, or animals.

---

Plasmodium Parasites

[Click Here for Sample Questions]

Plasmodium is a malarial parasite that infects the female anopheles mosquito and human beings. Inside the host’s body the plasmodium parasite undergoes several changes in its life cycle. To complete their life cycle, it requires two hosts- human and insect. They multiply in the liver and red blood cells of humans as well as in other mammals.

There are various plasmodium species known for causing malaria, but Plasmodium falciparum and Plasmodium vivax causes severe and life-threatening type of malaria in human. The internal structure of a plasmodium parasite is shown below in the figure: 

Plasmodium Parasite

---

Plasmodium Life Cycle

[Click Here for Sample Questions]

The plasmodium life cycle is completed in three stages namely: Gametocyte formation, sporozoites, and merozoites. This cycle occurs first in insects and then completed in human beings. The female anopheles mosquito initiates the lifecycle of plasmodium parasite. Microgametes (male gametocytes) and macrogametes (female gametocytes) are transferred through anopheles mosquito in the blood of host organism. The complete plasmodium life cycle is shown in the figure below in detail:

Life Cycle of Plasmodium

Stages of Plasmodium Lifecycle

Plasmodium, the parasite that causes malaria, has a life cycle that includes three stages and involves two hosts: humans and mosquitoes (Anopheles). The lifecycle of a plasmodium parasite which is completed in three stages is explained below in detail:

Stage 1: Gametocyte formation

In the initial stage of the life cycle of plasmodium, the female anopheles mosquito feeds on the blood meal and transfers the male gametocyte (microgametocytes) and female gametocyte (macrogametocyte).

• The male and female gametocytes convert into sporozoites inside the gut of mosquitoes.
• A crucial step in the Plasmodium life cycle, the gametocyte phase allows the parasite to move from its human host to its mosquito vector.
• The sporozoite parasite formation occurs after 15-18 days when the gametocytes have mated inside the gut of a mosquito.
• Control and eradication attempts for malaria focuses on targeting gametocytes as it disrupts the parasite's life cycle.

Stage 2: Sporozoite formation

The sporozoite is carried by the female anopheles mosquito. The Anopheles mosquito bites humans and injects sporozoites into the bloodstream. The completion of the parasite's transmission cycle depends on the mosquito's sporogonic phase, also known as the sporocyte phase, of the Plasmodium life cycle.

• These sporozoites enter the liver cell, divide asexually, and mature into schizonts. 
• Merozoites are released when the schizonts are ruptured, this is also called the pre-erythrocytic phase.
• The production of sporozoites, the infectious forms that carry on the malarial transmission, depends on the sporogonic cycle.

Stage 3: Merozoite formation 

Sporozites are injected into a person's bloodstream by an infected female Anopheles mosquito. After migrating to the liver, these sporozoites infiltrate hepatocytes, or liver cells. This is followed by the release of the rupture of liver cells. They enter the blood and divide via asexual mode.

• The damage of red blood cells leads to more production of merozoites and is called the erythrocytic stage.
• Merozoites secrete a poison that induces bone-shaking chills and fever when red blood cells are destroyed. 
• Extreme cold chills and fever characterize malaria in humans.

Mosquito Phase

This phase occurs sexually inside the midgut of a mosquito where the fusion of male and female gametocytes takes place to form a zygote. This zygote matures into an ookinete which enters the wall of the midgut to form an oocyst.

• Inside the oocyst, the ookinete nucleus divides repeatedly to form sporozoites.
• As soon as the infected mosquito sucks the blood for its meal, the sporozoites travel to its salivary glands.
• This cycle repeats when the sporozoites are injected into the new host (human) at subsequent mosquito bites.

---

Types of Plasmodium Parasites

[Click Here for Sample Questions]

There are about 120 plasmodium species that affect different vertebrate groups. Four species are considered true parasites as they use humans as a natural host. In this section, we will discuss the types of plasmodium species:

Plasmodium falciparum

One of the most poisonous species of plasmodium is P.falciparum as it is responsible for causing malignant malaria. If not treated at the earliest might even cause the death of an individual.

Plasmodium vivax

Another species is P.vivax which causes benign tertiary malaria. These are enlarged parasites and cause symptoms like headache, vomiting, shivers, etc.

Plasmodium ovale

A more compact parasite than P.vivax is the P.ovale parasite that can cause ovale malaria. It can last for a year if not treated at the earliest.

Plasmodium malariae

P.malariae symptoms include headache, shivers, nausea, anorexia, etc. If this disease is not treated it can last up to 20 years.

Types of Plasmodium Parasites

---

Things to Remember

• The plasmodium life cycle begins when the female anopheles mosquito feeds on the blood to nourish her eggs.
• The malaria parasite also affects chickens, monkeys, pigeons, and snakes.
• The parasitic stage where the red blood cells are infected is called merozoites.
• The life cycle of plasmodium includes both sexual and asexual stages.
• P.knowlesi is considered a zoonotic malaria.