Malaria
BiologyΒ· Unit 10: Infectious Diseases, Learning Outcome 10.4Β· 15 min read
1. Causal Pathogen and Transmissionβ β ββββ± 4 min
Malaria
A life-threatening febrile infectious disease caused by protist pathogens of the genus Plasmodium, transmitted to humans via female Anopheles mosquitoes. Plasmodium falciparum causes the most severe, life-threatening cases.
Example:
Over 240 million new cases and 600,000 deaths are reported annually, mostly in sub-Saharan Africa.
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.
Explain why male Anopheles mosquitoes cannot transmit malaria to humans.
- 1
- Recall the difference in feeding behavior between male and female mosquitoes:
- 2
Female mosquitoes need a blood meal high in protein to produce and mature their eggs, so they bite humans and other mammals to obtain blood.
- 3
Male mosquitoes feed exclusively on plant sap and nectar, and never bite humans to take blood meals.
- 4
- Link feeding behavior to pathogen transmission:
- 5
Transmission of Plasmodium occurs when an infected mosquito injects the pathogen into the human bloodstream during a bite. Since males never bite, they cannot transfer Plasmodium to new human hosts.
2. Life Cycle of *Plasmodium*β β β βββ± 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).
Definitive host
The host organism in which a parasite reaches sexual maturity and completes sexual reproduction.
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
Compare the roles of the mosquito and human host in the Plasmodium life cycle.
- 1
- Classify each host by type of reproduction:
- 2
Sexual reproduction of Plasmodium occurs only in the Anopheles mosquito, which is the definitive host. Asexual reproduction (multiple fission) occurs in human liver and red blood cells, so humans are the intermediate host.
- 3
- State the transmission role of each:
- 4
The mosquito acts as the vector, carrying Plasmodium between human hosts. Humans act as the reservoir for the pathogen, allowing asexual stages to persist between bites.
3. Global Impact and Distributionβ β ββββ± 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 Strategiesβ β β βββ± 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
Explain why draining standing water reduces the incidence of malaria.
- 1
- Recall where Anopheles mosquitoes develop:
- 2
Anopheles mosquito larvae develop in stagnant, standing water such as puddles, ponds, irrigation ditches and open containers.
- 3
- Link habitat removal to mosquito population size:
- 4
Draining standing water removes the required habitat for larvae to develop into adult biting mosquitoes, reducing the total Anopheles population.
- 5
- Connect to malaria transmission:
- 6
A smaller mosquito population reduces the frequency of bites and Plasmodium transmission between humans, lowering the overall incidence of malaria.
5. Common Pitfalls
Wrong move:
Claiming the Anopheles mosquito is the only host of Plasmodium
Why:
Plasmodium requires two hosts to complete its life cycle, both play essential roles in development
Correct move:
State that the Anopheles mosquito is the definitive host/vector, and humans are the intermediate host where asexual reproduction occurs
Wrong move:
Claiming male Anopheles mosquitoes can transmit malaria
Why:
Only females bite humans to take blood meals required for egg development; males feed only on nectar
Correct move:
Only female Anopheles mosquitoes transmit malaria between human hosts
Wrong move:
Claiming malaria spreads directly between humans without a vector
Why:
Natural transmission requires the Anopheles vector; direct transmission via blood transfusion or congenital spread is extremely rare
Correct move:
Malaria is primarily a vector-borne disease transmitted by the bite of an infected female Anopheles mosquito
Wrong move:
Stating antibiotics are used to treat malaria
Why:
Malaria is caused by a eukaryotic protist, not a prokaryotic bacterium, so antibiotics have no effect
Correct move:
First-line treatment for uncomplicated malaria uses artemisinin combination therapies (ACTs) that target Plasmodium directly
6. Quick Reference Cheatsheet
Key Concept | Core Fact | CIE Exam Note |
|---|---|---|
Causal pathogen | Plasmodium (protist) | Eukaryote β antibiotics do not work |
Vector | Female Anopheles mosquito | Males do not bite/transmit |
Host roles | Mosquito = definitive (sexual), Human = intermediate (asexual) | Always specify roles for full marks |
Top control methods | ITNs, IRS, drain standing water, ACT treatment | Name 2+ for 4+ mark questions |
High risk groups | Under 5s, pregnant women | Common 2-mark exam question |
7. Frequently Asked
Why can't antibiotics treat malaria?
Malaria is caused by Plasmodium, a eukaryotic protist, not a prokaryotic bacterium. Antibiotics target structures unique to prokaryotes, so they have no effect on Plasmodium cells.
When this came up on past exams
AI-estimated based on syllabus patterns β cross-check with official past papers for accuracy. Use only as revision-focus signals.
- 2022 Β· 22
Describe transmission of malaria
- 2021 Β· 12
Outline malaria control methods
- 2023 Β· 21
Describe Plasmodium life cycle
Going deeper
What's Next
Understanding malaria builds a foundation for exploring other major global infectious diseases, the evolution of drug and insecticide resistance in pathogens, and the design of public health strategies to control communicable disease. This topic also connects to core concepts of evolution by natural selection, seen in selection for the sickle cell allele in endemic regions. Next, you can explore other high-frequency infectious diseases in the CIE 9700 syllabus, or dive deeper into immunity and vaccine development.