Malaria — Biology
1. Causal Pathogen and Transmission ★★☆☆☆ ⏱ 4 min
Malaria is an anthroponotic disease, meaning humans are the primary reservoir for the pathogen. Only female *Anopheles* mosquitoes transmit malaria: they require protein from human blood meals to develop their eggs, so they bite humans. Male mosquitoes feed only on plant nectar and do not bite.
2. Life Cycle of *Plasmodium* ★★★☆☆ ⏱ 5 min
*Plasmodium* has a complex digenetic life cycle, meaning it requires two different host species to complete its sexual and asexual stages of development. The *Anopheles* mosquito is the definitive host (where sexual reproduction occurs), and humans are the intermediate host (where asexual reproduction occurs).
- An infected female *Anopheles* injects *Plasmodium* sporozoites into the human bloodstream during a bite
- Sporozoites travel to the liver, invade hepatocytes (liver cells), and multiply asexually to form merozoites
- Merozoites leave the liver, invade red blood cells, and multiply asexually until the red blood cell lyses
- Lysis of red blood cells releases toxins, triggering the characteristic cycles of fever and chills
- Some merozoites develop into gametocytes, which are taken up by a new *Anopheles* mosquito during a blood meal
- Gametocytes mature into gametes in the mosquito gut, fuse to form a zygote, and develop into new sporozoites that migrate to the salivary glands
3. Global Impact and Distribution ★★☆☆☆ ⏱ 3 min
Malaria is endemic in tropical and subtropical regions between the Tropics of Cancer and Capricorn. This distribution matches the habitat requirements of *Anopheles* mosquitoes, which need warm, humid climates and standing water for larval development.
Children under 5 years old and pregnant women are at highest risk of severe disease and death: children have not yet built immunity to *Plasmodium*, and pregnancy suppresses immune function. Malaria traps communities in poverty by reducing work productivity and increasing healthcare costs.
4. Control and Treatment Strategies ★★★☆☆ ⏱ 3 min
Malaria control targets both the mosquito vector and the *Plasmodium* pathogen, using a combination of strategies to reduce transmission and treat infections:
- **Vector control**: Insecticide-treated bed nets (ITNs) prevent bites during peak feeding hours, and indoor residual spraying (IRS) kills resting mosquitoes
- **Chemoprevention**: Anti-malarial drugs are given to high-risk groups in endemic areas to prevent infection
- **Treatment**: Artemisinin combination therapy (ACT) is the first-line treatment for uncomplicated *P. falciparum* malaria
- **Habitat modification**: Draining standing water removes breeding sites for mosquito larvae
Common Pitfalls
Why: *Plasmodium* requires two hosts to complete its life cycle, both play essential roles in development
Why: Only females bite humans to take blood meals required for egg development; males feed only on nectar
Why: Natural transmission requires the *Anopheles* vector; direct transmission via blood transfusion or congenital spread is extremely rare
Why: Malaria is caused by a eukaryotic protist, not a prokaryotic bacterium, so antibiotics have no effect