Malaria is caused by a group of related intracellular protozoan pathogens of the genus Plasmodium. These species exhibit a complex life cycle reliant on a mammalian host and anopheles mosquito vector. In the human host they are obligate intracellular pathogens infecting initially the liver in the sporozoite form. In the liver the parasites replicate and develop into merozoites which are then released into the blood stream. These infect the erythrocyte and begin a restricted life cycle. Each parasite may develop into a schizont (a cluster of infectious units which may invade further erythrocytes) or a gametocyte (the sexual form which may be transferred to the anopheles mosquito upon taking a blood meal). Re-infection of the liver does not occur.
Suspected malaria is a medical emergency. Sampling and processing of the blood sample must not be delayed if malaria is suspected. Five primary species of malaria have been identified in humans: P.falciparum, P.vivax, P.ovale P.malariae and P.knowlesi. Their geographic distribution is unique for each species.
Blood should ideally be taken direct from the patient’s finger or ear & the films prepared at the bedside or in the clinic. When this is not possible blood taken into anticoagulant (EDTA) can be used. Thick & thin blood films should be made as soon as possible, certainly less than 2 hours after the EDTA blood was drawn, to minimise morphological changes in the parasites. Parasite and red cell morphology can be seriously affected if the blood has been in anticoagulation for too long.
Where there is a strong clinical suspicion if the first films are negative, blood should be taken and films made and checked at least two times over the first 24 hours and further films examined every 12 hours after that if strongly clinically indicated.
Preparation of patients:
Travel history should be recorded, and any clinical details recorded on the request form.
In symptomatic patients please phone the laboratory prior to sending the sample.
Precautions: Global distribution of malaria is restricted to areas endemic to the anopheles mosquito. Latent infections of some species may occur due to hypnozoites stored in the liver. P. knowlesi is morphologically indistinguishable from P. malariae on blood film preparations.
