Question

Give the scientific name of the parasite that Causes malignant malaria in humans. At what stage does this parasite enter the human body? Trace its life cycle in human body.

Answer 1

Plasmodium falciparum causes malignant terrain or subtertian malaria, characterized by fever cycles every 36-48hr. This infection is the most serious as it affects the brain and can be fatal.

Life cycle of Plasmodium

• The sporozoites of Plasmodium are infected into the human blood when its vector, a female Anopheles mosquito bites the person.

• These sporozoites then enter into the liver through blood circulation.

• In liver, they multiply sexually and rupture the liver cells and are released into the blood, where they attack fresh red blood cells. These are called merozoites.

• Inside the RBCs, merozoites develop through a ring stage of form a schizont (or trophozoites).

• Schizont divides further to form 8-24 merozoites.

• When the schizont is mature, the RBC's burst to release merozoites into the blood.

• The rupture of RBC's is associated with the release of a toxic substance, haemozoin.

• This haemozoin is responsible for the chills and high fever recurring every 3-4 days.

• Some merozoites do not develop into the schizont. Instead, they develop into immature sexual stages called gametocytes. During a mosquito bite, these are sucked by the female Anopheles.

• The male and female gametocytes fertilize and develop in the mosquito's intestine into the mature infective stage called sporozoite.

• The sporozoites escape from the intestine and moves to the salivary glands of the mosquito.

• When this infected mosquito bites another human, these sporozoites are injected into the blood through the saliva and start the liver and RBC's cycle again.

Thus the Plasmodium completes its life cycle into two hosts man and mosquito. In human, the life cycle is asexual and in mosquito it is sexual.