Malaria kills a child every two minutes. Not because we lack the knowledge to prevent it — we have bed nets, insecticides, antimalarial drugs, and a working vaccine. It persists because of poverty, geography, and the relentless pressure of natural selection on both the parasite and the mosquito.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
Malaria kills more people annually than any armed conflict currently ongoing. Yet it is both preventable and treatable. Dengue infects 390 million people per year — four times more than malaria — yet has only recently had a partially effective vaccine approved.
Before reading: why do you think diseases like malaria and dengue persist despite decades of effort to control them? Predict at least three reasons — biological, social, or economic.
Come back to this at the end of the lesson.
Wrong: The immune system always remembers every pathogen it encounters.
Right: Immunological memory is specific; the body remembers previously encountered antigens, not all pathogens.
Core Content
Malaria is caused by Plasmodium parasites — single-celled eukaryotes (not bacteria or viruses) transmitted by infected female Anopheles mosquitoes. Five species infect humans; P. falciparum causes the most severe and lethal form.
In 2022, there were an estimated 249 million malaria cases globally, causing approximately 608,000 deaths — 76% of which were children under five. Sub-Saharan Africa bears approximately 95% of the global malaria burden.
Each life cycle stage offers a different intervention point — vector control (mosquito), vaccines (liver stage), drugs (blood stage)
| Strategy | Mechanism | Effectiveness | Limitations |
|---|---|---|---|
| Insecticide-treated bed nets (ITNs) | Pyrethroid kills mosquitoes contacting net; physical barrier prevents bites during sleep | ~50–60% reduction in child malaria mortality in high-use areas | Pyrethroid resistance growing; must be used consistently; periodic re-treatment needed |
| Indoor residual spraying (IRS) | Insecticide sprayed on interior walls kills resting mosquitoes | Very effective in targeted programs; contributed to historic reductions | Insecticide resistance; community acceptance; logistical complexity |
| Artemisinin combination therapy (ACT) | Rapidly kills blood-stage parasites | Gold-standard treatment; highly effective when taken correctly | Artemisinin partial resistance emerging in Southeast Asia and Africa |
| RTS,S vaccine (Mosquirix) | Targets sporozoite surface protein — blocks liver-stage invasion | ~36% efficacy against clinical malaria in young children | Requires 4-dose schedule; waning immunity; modest efficacy |
| R21/Matrix-M vaccine | Next-generation vaccine — higher antigen density than RTS,S | ~75–80% efficacy in trials; WHO approved 2023 — most effective malaria vaccine to date | Still requires booster; scale-up ongoing |
Dengue fever is caused by dengue virus (DENV), a flavivirus with four distinct serotypes (DENV-1, 2, 3, 4). It is transmitted by Aedes aegypti mosquitoes — urban mosquitoes that breed in small water containers and bite during the day. Dengue infects an estimated 390 million people per year; approximately 96 million develop clinical illness and around 20,000 die. It is endemic in over 100 countries and cases have increased eightfold since 2000.
Infection with one dengue serotype provides lifelong immunity to that serotype but only short-term cross-protection against the others. A second infection with a different serotype can cause antibody-dependent enhancement (ADE) — pre-existing antibodies from the first infection facilitate entry of the second serotype into immune cells, amplifying the infection. This causes severe dengue (dengue haemorrhagic fever), which can be fatal.
A dengue vaccine must therefore provide strong, balanced, long-lasting immunity against all four serotypes simultaneously. If it protects well against only some serotypes, vaccinated individuals could be immunologically primed for ADE — worse off than if unvaccinated.
In 2022, malaria killed approximately 608,000 people. Roughly 76% were children under five. The arithmetic is blunt: one child every two minutes, around the clock, every day of the year.
You will analyse control strategy data in Activity 01 and evaluate these diseases in Short Answer Q3.
Misconception: Malaria is caused by a virus or bacterium.
Malaria is caused by Plasmodium — a eukaryotic protozoan parasite. Antibiotics do not treat malaria (Plasmodium is not a bacterium) and antivirals do not treat it (it is not a virus). Antimalarial drugs target specific parasite enzymes unique to Plasmodium. The eukaryotic complexity of the parasite is one reason developing effective vaccines and drugs has been so challenging.
Misconception: If you have had dengue once, you are immune to all future dengue infections.
Immunity is serotype-specific — you develop lifelong immunity to the serotype you were infected with, but only short-term cross-protection against the other three. A second infection with a different serotype can cause ADE, where pre-existing antibodies paradoxically facilitate the second infection — potentially causing severe dengue. Prior dengue exposure is a risk factor, not just protection.
Misconception: Developing a vaccine for a disease automatically solves the problem.
Vaccines are a critical tool but not automatically a solution. The malaria RTS,S vaccine took 30 years of development and has only ~36% efficacy. The dengue vaccine Dengvaxia caused harm in seronegative individuals. Even effective vaccines require cold chains, delivery infrastructure, community acceptance, and sustained funding. Biological complexity, delivery challenges, and economics all determine whether a vaccine reduces real-world disease burden.
Malaria and Dengue — Global Burden
Activities
The table below shows malaria case rates, deaths, and key intervention scale-up data for sub-Saharan Africa from 2000 to 2022.
| Year | Cases per 100,000 | Deaths per 100,000 | % households with ITN | ACT available? |
|---|---|---|---|---|
| 2000 | 370 | 121 | 2% | No |
| 2005 | 345 | 98 | 18% | Partially |
| 2010 | 270 | 64 | 48% | Yes |
| 2015 | 218 | 51 | 65% | Yes |
| 2019 | 224 | 55 | 62% | Yes |
| 2020 | 238 | 62 | 60% | Yes (disrupted) |
| 2022 | 231 | 58 | 63% | Yes |
Write your responses here or in your book.
A student wrote the following passage about malaria and dengue. It contains four factual errors. Identify each, explain what is wrong, and write the correction.
"Malaria is caused by a virus called Plasmodium falciparum, which is transmitted by the bite of infected male Anopheles mosquitoes. Once inside the human body, the parasite enters red blood cells directly from the bloodstream, skipping the liver stage entirely. Dengue fever is caused by a single viral serotype, so a person who has had dengue once is fully immune to all future dengue infections. The dengue vaccine Dengvaxia was found to be safe and highly effective in all populations regardless of prior dengue exposure."
Write your responses here or in your book.
You were asked to predict why malaria and dengue persist despite decades of control effort.
The biological reasons: drug and insecticide resistance (natural selection making tools progressively less effective); complex multi-stage life cycles requiring multiple simultaneous interventions; dengue's four serotypes and ADE making vaccination paradoxically risky; partial immunity that doesn't prevent re-infection.
The structural reasons: most burden falls on the world's poorest countries — those least able to fund comprehensive control programs. Remote geography limits access. Climate change expands vector ranges. COVID-19 disrupted delivery systems. No new antibiotic class since 1987; vaccine development takes decades and costs billions.
The lesson: biological innovation alone is not sufficient. A vaccine that works biologically fails if it can't reach people. A tool that reaches people fails if resistance has made it less effective. Solving these diseases requires simultaneous biological innovation and structural investment — which is why malaria, despite having two approved vaccines and effective drugs, still kills a child every two minutes.
Assessment
5 random questions from a replayable lesson bank — feedback shown immediately
1. Describe the life cycle of Plasmodium falciparum, identifying at least three stages and explaining how each creates an opportunity for disease control. (3 marks)
2. Explain why dengue is more difficult to vaccinate against than malaria. Refer to the number of serotypes, antibody-dependent enhancement, and the Dengvaxia program. (3 marks)
3. Evaluate the effectiveness of integrated malaria control in sub-Saharan Africa between 2000 and 2022. Describe evidence of success, explain why progress has stalled since 2015, and assess the potential impact of the R21 vaccine. (4 marks)
Answers
SA1 marking guide: 1 mark per stage correctly identified with intervention opportunity (max 3): mosquito + vector control; liver + primaquine/RTS,S/R21; blood + ACT
SA1: The Plasmodium falciparum life cycle alternates between mosquito and human hosts. Stage 1 — the mosquito stage: sporozoites develop in the mosquito's salivary glands after sexual reproduction in the mosquito gut. This stage is targeted by vector control — insecticide-treated bed nets and indoor residual spraying kill or repel Anopheles mosquitoes before they can deliver sporozoites in an infected bite. Stage 2 — the liver stage: sporozoites injected during a bite rapidly migrate to the liver, invading hepatocytes and multiplying asexually to produce thousands of merozoites. No symptoms occur. The drug primaquine kills liver-stage parasites. The RTS,S and R21 vaccines block sporozoite invasion of liver cells by stimulating antibodies against the circumsporozoite protein — eliminating parasites before the symptomatic blood stage begins. Stage 3 — the blood stage: merozoites released from the liver invade red blood cells, multiply, rupture the cells (causing the characteristic fever and anaemia of malaria), and release more merozoites. ACT (artemisinin combination therapy) kills blood-stage parasites rapidly, treating illness and reducing transmission by limiting gametocyte production.
SA2 marking guide: 1 mark: 4 serotypes — balanced protection required | 1 mark: ADE mechanism — partial protection creates severe dengue risk | 1 mark: Dengvaxia harm in seronegative individuals — program halted
SA2: Dengue is more difficult to vaccinate against than malaria for three interconnected reasons. First, dengue virus has four antigenically distinct serotypes (DENV-1, 2, 3, 4). A vaccine must provide strong, balanced, lasting immunity against all four simultaneously — a far more complex immunological target than the relatively stable sporozoite protein targeted by the malaria vaccines. Second, the phenomenon of antibody-dependent enhancement (ADE) creates a paradoxical risk. If a vaccine provides immunity against some serotypes but not others, vaccinated individuals may be worse off than unvaccinated — pre-existing antibodies from the vaccine-induced response can facilitate entry of unprotected serotypes into Fc receptor-bearing immune cells, amplifying the infection and potentially causing severe dengue haemorrhagic fever. Third, the Dengvaxia program in the Philippines demonstrated this risk in practice. Given to over 800,000 schoolchildren in 2016, including many who had never previously had dengue (seronegative), subsequent analysis showed seronegative recipients were at higher risk of severe dengue after vaccination — exactly the ADE effect. The program was halted, criminal investigations were launched, and Dengvaxia is now recommended only for seropositive individuals — the opposite of the original target population.
SA3 marking guide: 1 mark: success evidence with specific data (deaths 121→51 per 100,000; case reduction) | 1 mark: reasons for stall (ITN plateau, resistance, COVID-19) | 1 mark: R21 potential at scale | 1 mark: overall evaluative conclusion
SA3: Between 2000 and 2015, integrated malaria control programs in sub-Saharan Africa achieved substantial progress. Malaria deaths per 100,000 fell from 121 to 51 — a reduction of approximately 58% — as insecticide-treated bed net coverage increased from 2% to 65% of households and ACT became widely available. Case numbers also fell from ~370 to ~218 per 100,000. This represented millions of lives saved and one of global health's most significant achievements in the early 21st century. Since 2015, however, progress has stalled. Death rates stabilised in the 51–62 range rather than continuing to decline. ITN coverage plateaued at approximately 62–65% of households — logistical, funding, and population growth constraints appear to have limited further scale-up. Pyrethroid resistance in Anopheles populations is progressively reducing the killing effectiveness of treated nets in many areas. Artemisinin partial resistance, first detected in Southeast Asia, is increasingly found in African P. falciparum populations, threatening the gold-standard treatment. The COVID-19 pandemic in 2020 severely disrupted malaria service delivery — the data show a notable spike in both cases (238 per 100,000) and deaths (62 per 100,000) in that year, despite ACT nominally remaining available. The R21/Matrix-M vaccine, with approximately 75–80% efficacy approved by the WHO in 2023, has the potential to significantly accelerate malaria control beyond what bed nets and drugs alone can achieve. If deployed at scale — particularly to children under five, who bear 76% of malaria deaths — it could drive substantial further reductions in mortality even in areas where insecticide and drug resistance is limiting existing tools. Cold chain requirements, healthcare system capacity, and sustained funding remain constraints on deployment. Overall, the 2000–2015 period demonstrates what sustained, scaled investment in integrated malaria control can achieve. The post-2015 stall is a serious warning: without new tools, continued investment, and strategies to address resistance, the gains of the previous decade risk being eroded by biology and demography.
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