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May 26th, 2022Hi there!
You’re looking at a short reference article from Explain Medicine (one of four distinct learning formats available in Clinical Odyssey). Try it out, and have fun improving your clinical skills.
Introduction
Malaria is a mosquito-borne protozoan infection caused by Plasmodium spp.. These are transmitted to humans via species of the Anopheles mosquito. Malaria is most prevalent in Africa, Asia, South America, and Melanesia, with most deaths occurring in sub-Saharan Africa.
Incubation period
The incubation period is 9-14 days for P. falciparum and P. knowlesi, 12-17 days for P. vivax and P. ovale, and up to 40 days for P. malariae.
Febrile episodes
Febrile episodes are caused by the cyclic rupture (between 24-72 hours, depending on species) of mature schizonts in the blood. Schizonts release pyrogens, resulting in cytokine activation. Since parasite population dynamics within the host are not synchronous, the fevers are rarely as periodic as the erythrocytic cycles. Note that most patients seek medical care before fever cycles become fully established.
Uncomplicated malaria
Patients with uncomplicated malaria may present with non-specific flu-like symptoms, such as headache, cough, myalgia, abdominal pain, and diarrhea. These are due to the release of proinflammatory mediators.
Complicated malaria
Complicated malaria can present with cerebral malaria, acute respiratory distress syndrome, severe anemia, jaundice, and acute renal failure. In children, severe malaria can also present with severe anemia and metabolic acidosis.
Cerebral malaria
Patients with cerebral malaria due to P. falciparum or P. knowlesi can develop confusion, drowsiness, convulsions, and coma. This is due to cerebral tissue hypoxia secondary to microvascular obstruction and endothelial activation. P. falciparum erythrocyte membrane protein 1 (PfEMP1) is expressed on the surface membrane of infected red blood cells. These bind to the endothelium of blood vessels, leading to microvascular obstruction, increased blood-brain barrier permeability, release of proinflammatory cytokines, and cerebral edema. Note that the shorter erythrocytic cycle of P. knowlesi (24 hours vs 48-72 hours for P. falciparum) predisposes to a daily increase in parasitemia, and thus, more severe symptoms.