Malaria

Malaria is a vector-borne protozoal disease caused by Plasmodium parasites transmitted to humans by the bite of infected female Anopheles mosquitoes. Five species infect humans, with Plasmodium falciparum and Plasmodium vivax responsible for most disease; falciparum malaria can progress to severe, life-threatening illness, while vivax can relapse from dormant liver stages. It remains one of the largest causes of infectious-disease morbidity and mortality worldwide.

Definition

Malaria is infection by protozoan parasites of the genus Plasmodium, transmitted by female Anopheles mosquitoes, in which parasites replicate first in hepatocytes and then cyclically in erythrocytes, producing fever, haemolysis, and, in severe falciparum disease, organ dysfunction.

Scope

This entry covers the Plasmodium life cycle (liver and blood stages, mosquito transmission), the species that infect humans, the basis of the cyclical fever and of severe malaria, and the broad epidemiology and control of the disease. It treats malaria as a reference topic within parasitic and tropical infectious disease and cross-links the protozoal-infections overview. It is not clinical or prescribing guidance.

Key concepts

• Plasmodium species (falciparum, vivax, malariae, ovale, knowlesi)
• Anopheles mosquito vector
• Liver (exo-erythrocytic) and blood stages
• Erythrocytic schizogony and cyclical fever
• Severe and cerebral malaria
• Hypnozoites and relapse in vivax
• Transmission intensity and endemicity

Mechanisms

Infection begins when sporozoites injected by a feeding Anopheles mosquito travel to the liver and multiply within hepatocytes; the resulting merozoites are released into the blood and invade erythrocytes, where repeated cycles of asexual replication (schizogony) rupture red cells and produce the characteristic recurrent fever (white-2014). In Plasmodium falciparum, infected erythrocytes adhere to vascular endothelium (sequestration), which underlies severe complications including cerebral malaria, severe anaemia, and organ failure. Plasmodium vivax and ovale form dormant liver-stage hypnozoites that can reactivate to cause relapses weeks to months later. Sexual-stage gametocytes taken up by a mosquito complete the cycle, linking individual infection to onward transmission (white-2014).

Clinical relevance

Malaria is a leading cause of febrile illness and death in endemic regions and an important consideration in the returning traveller; severe falciparum malaria is a medical emergency. This entry characterizes the disease and its biology for orientation and evidence appraisal and is not a basis for individual diagnosis, dosing, or treatment decisions (white-2014).

Epidemiology

Malaria is endemic across much of sub-Saharan Africa, South and Southeast Asia, and parts of Latin America and Oceania, with the heaviest falciparum burden in Africa and a large share of deaths among young children. Transmission intensity varies sharply by geography and has shifted with the scale-up of insecticide-treated nets, indoor residual spraying, and effective treatment, as documented in continent-wide analyses of falciparum transmission (noor-2014). Control sits within the broader neglected-tropical-disease and global-health agenda (hotez-2007).

Evidence & guidelines

Clinical and programmatic practice is anchored by World Health Organization malaria guidelines, which are periodically updated; the references here are orienting reviews and epidemiological analyses rather than treatment protocols (white-2014; noor-2014).

History

Malaria has afflicted humans throughout recorded history; its name derives from the belief that it arose from bad air (mal aria) of marshes. The parasite was identified in blood in 1880 and its mosquito transmission established around the turn of the twentieth century, work recognized by early Nobel Prizes. The twentieth and twenty-first centuries saw cycles of control, the spread of drug and insecticide resistance, and renewed elimination efforts supported by vector control, artemisinin-based therapy, and, more recently, vaccines (white-2014; noor-2014).

Key figures

• Nicholas White
• Arjen Dondorp
• Robert Snow
• Abdisalan Noor

Seminal works

• white-2014
• noor-2014

Frequently asked questions

Why does malaria cause recurrent fever?

The fever corresponds to the synchronized rupture of infected red blood cells at the end of each erythrocytic replication cycle, which releases parasites and triggers the host inflammatory response (white-2014).

Why can vivax malaria relapse?

Plasmodium vivax (and ovale) form dormant liver-stage parasites called hypnozoites that can reactivate weeks to months after the initial infection, producing relapses without a new mosquito bite (white-2014).