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close this bookBasic Malaria Microscopy (part I and II) (WHO - OMS, 1991, 72 p.)
View the document(introduction...)
View the documentPreface
View the documentIntroduction
View the documentLearning Unit 1. Malaria, the disease
View the documentLearning Unit 2. Cleaning and storing microscope slides
View the documentLearning Unit 3. Keeping accurate records
View the documentLearning Unit 4. Blood films
View the documentLearning Unit 5. Staining blood films with Giemsa stain
View the documentLearning Unit 6. The microscope
View the documentLearning Unit 7. Examining blood films
View the documentLearning Unit 8. Examining blood films for malaria parasites
View the documentLearning Unit 9. Artefacts in blood films
View the documentLearning Unit 10. Routine examination of blood films for malaria parasites
View the documentLearning Unit 11. Life cycle of the malaria parasite
View the documentLearning Unit 12. Supervisory aspects of malaria microscopy
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Learning Unit 11. Life cycle of the malaria parasite

Learning objectives

By the end of this Unit you should be able to:

· describe the life cycle of the malaria parasite in humans

· describe that part of the life cycle which is spent in the female Anopheles mosquito (the vector of malaria)

· recall the various stages of the malaria parasite found in human blood.

In humans

The liver phase

When an infected female Anopheles mosquito bites a human being, malaria parasites are introduced into that person.

The parasites move quickly to the liver, where each invades a liver cell. Over a period of 7-21 days the parasite grows and reproduces. Finally the liver cell bursts, releasing parasites into the bloodstream, where each attaches to and invades a red blood cell.

This description is invariably true of Plasmodium falciparum and P. malariae infections. In P. vivax and P. ovale infections, however, some of the parasites remain in the liver and do not reproduce immediately. It is these dormant parasites that are responsible for the relapses that occur in patients with P. vivax and P. ovale infections.

The blood phase

From the work you have done in earlier Learning Units you will already be familiar with the different stages of the blood phase, which are shown diagrammatically in Fig. 5.

In the mosquito

The sexual phase of the malaria life cycle takes place in the stomach of the mosquito. Soon after the female Anopheles mosquito has ingested blood from an infected person, the male gametocytes (microgametocytes) each produce 4-8 flagella. These flagella enter, and fertilize, the female gametocytes (macrogametocytes). The mobile products of this fertilization burrow through the stomach wall and develop into cysts in the lining of the abdomen. When the cysts rupture, they release sporozoites which eventually enter the salivary glands. After a period of time which varies according to the species of mosquito and the ambient temperature but which is usually between 7 and 14 days, the anopheline mosquito is able to transmit malaria.