What Is Malaria?

Malaria is an infectious disease caused by single-celled parasites of the genus Plasmodium and transmitted to humans through the bite of infected female Anopheles mosquitoes. Five species infect people, and Plasmodium falciparum accounts for the great majority of severe disease and death, particularly in sub-Saharan Africa. Plasmodium vivax is more widely distributed geographically and forms dormant liver stages that cause relapses months after the initial infection. The World Health Organization fact sheet on malaria describes a clinical course that begins with fever, chills, and headache and can progress within 24 hours to severe anemia, cerebral malaria, respiratory distress, or organ failure if falciparum infection goes untreated.

The disease remains one of the largest burdens in global health. WHO's world malaria report series tracks hundreds of millions of cases and well over half a million deaths annually, concentrated overwhelmingly in the African Region and falling most heavily on children under five and on pregnant women.

The Parasite Life Cycle

Malaria has a two-host life cycle that alternates between mosquito and human. A feeding mosquito injects sporozoites, which travel in the bloodstream to the liver and invade hepatocytes, where each matures into a schizont containing thousands of merozoites. Rupture releases merozoites into the blood, beginning the erythrocytic stage in which parasites invade red blood cells, develop through ring and trophozoite forms, and burst out in synchronized waves that produce the characteristic periodic fever. A fraction of blood-stage parasites differentiate into male and female gametocytes, which a subsequent mosquito ingests; fertilization and development in the mosquito midgut eventually produce sporozoites that migrate to the salivary glands. The CDC laboratory reference on the malaria life cycle sets out each of these stages together with the morphology used to identify species under the microscope.

Diagnosis and Detection

Definitive diagnosis requires demonstrating parasites or their antigens. Light microscopy of Giemsa-stained thick and thin blood films remains the reference method, allowing species identification and quantification of parasite density, but it depends on trained microscopists and good slide preparation. Rapid diagnostic tests, lateral-flow immunochromatographic strips that detect parasite antigens such as histidine-rich protein 2, made point-of-care testing feasible across rural clinics, and hundreds of millions are distributed each year. Their weakness is that deletions of the hrp2 and hrp3 genes in some parasite populations produce false negatives, which has pushed programs toward tests targeting additional antigens. Nucleic acid amplification methods offer higher sensitivity for low-density and asymptomatic infections, and automated digital microscopy with machine learning classifiers is an active area of instrumentation research.

Treatment, Resistance, and Control

Artemisinin-based combination therapy is the first-line treatment for uncomplicated falciparum malaria, pairing a fast-acting artemisinin derivative with a longer-lasting partner drug. Partial artemisinin resistance, first documented in the Greater Mekong subregion and since detected in East Africa and South America, threatens that strategy, and the CDC overview of antimalarial drug resistance describes the molecular markers and surveillance used to track it. Prevention rests on vector control through insecticide-treated bed nets and indoor residual spraying, on chemoprevention for children and pregnant women, and increasingly on the RTS,S and R21 vaccines now being deployed in endemic countries. Insecticide resistance in Anopheles populations and the spread of the urban-adapted vector Anopheles stephensi complicate all of this.

Applications

Malaria research and control draw on and contribute to fields including:

• Point-of-care diagnostic device and microfluidic biosensor engineering
• Automated microscopy and computer vision for parasite detection and counting
• Epidemiological modeling, geospatial analysis, and remote sensing of vector habitat
• Drug discovery, medicinal chemistry, and vaccine development
• Genetic vector control, including gene drive and sterile insect approaches
• Health information systems for surveillance, stock management, and case reporting