17th June 2024

Background

Malaria is a tropical protozoal infection transmitted by the female anopheles mosquito. Plasmodium falciparum is the deadliest species. Plasmodium ovale and Plasmodium vivax both have dormant hypnozoite stages in the liver and so require a targeted drug such as primaquine for full eradication. Plasmodium malariae and Plasmodium knowlesi are the other two species known to cause human disease. Untreated malaria can cause fevers that correspond to the timing of rupture of schizonts in the bloodstream. P. ovale, P. vivax, and P. falciparum are known as tertian infections, classically causing a fever every 48 hours. P. malariae is a quartan malaria, causing a fever every 72 hours. P.knowlesi causes a fever every 24 hours.

Malaria can present non-specifically and should be included in most differentials of fever in the returned traveller. Features of severe malaria are discussed below and can be a clue to the diagnosis. Falciparum malaria is thought to exert its severe effects through a process called sequestration, whereby infected erythrocytes adhere to endothelial walls. Malarial retinopathy is indicative of cerebral malaria. Recurrent malarial infections can cause massive splenomegaly.