prevalence and risk factors of malaria

Pathogenic Diseases – Malaria: Prevalence, Risk Factors and Geographical Context

1. Why Study Malaria in Geography?

• Shows the interaction between physical environment, human activity and health outcomes.
• Provides a real‑world case study for the **Disease & Geography** global theme (Topic 10, Paper 4).
• Links to **Tropical Environments** (Topic 7, Paper 3) through climate, vegetation and ecosystem processes.
• Illustrates concepts from **Hydrology & River Processes** (Paper 1) and **Water‑resource Management** (Paper 2).
• Offers data for practising AO1 (knowledge), AO2 (analysis) and AO3 (evaluation) skills.

2. Link to Cambridge Syllabus – Topic 10 (Disease & Geography)

Each sub‑section below is mapped to the assessment objectives of Paper 4:

• AO1 – Terminology & concepts: definitions of prevalence, incidence, vector, reservoir, etc.
• AO2 – Data analysis: incidence tables, case‑study data set, mapping of spatial patterns.
• AO3 – Evaluation: effectiveness, cost‑effectiveness, sustainability, equity and governance of control measures.

3. Measuring Malaria Prevalence

Prevalence is expressed as the number of confirmed cases per 1 000 population at risk in a given year. The related incidence rate is calculated as:

Incidence = (Number of new cases) ÷ (Population at risk × Time)

Incidence can be examined at different scales – village, district, national and global – to reveal spatial patterns and trends over time.

4. Global Distribution (2023 Estimates)

5. Physical Geography Links

5.1 Hydrology & River‑Basin Systems (Paper 1)

• Standing water – puddles, rice paddies, irrigation canals provide breeding sites for Anopheles mosquitoes.
• Drainage‑basin characteristics – flat terrain, low gradient and poor natural drainage increase the extent of stagnant water.
• Seasonal flooding expands habitat for vectors, a clear cause‑effect relationship.

Schematic description (to be drawn by students): a simple basin diagram showing inputs (rainfall), stores (soil moisture, surface water, rice fields), and transfers (run‑off, irrigation canals). Highlight where mosquito larvae develop.

5.2 Atmospheric Processes (Paper 3 – Tropical Environments)

• Temperature 20‑30 °C shortens the extrinsic incubation period of Plasmodium inside the mosquito.
• Relative humidity > 60 % prolongs adult mosquito lifespan, increasing transmission potential.
• ITCZ and monsoon patterns create the warm, humid climate envelope that defines malaria‑endemic zones.
• Climate change can shift this envelope, allowing vectors to colonise higher altitudes and previously temperate regions.

5.3 Tropical Environments (Topic 7 – Paper 3)

Malaria is largely confined to the **tropical climate belt** where:

• Mean annual temperature exceeds 18 °C.
• Seasonal rainfall is sufficient to maintain permanent or semi‑permanent water bodies.
• Vegetation types (e.g., savanna, mangrove, tropical rainforest) influence micro‑climates and mosquito resting sites.

6. Human Geography Links (Paper 2)

6.1 Population Distribution & Vulnerability

• Rural‑agricultural zones have high population density and close proximity to vector habitats.
• Children under five and pregnant women suffer higher morbidity – an illustration of Diversity & Equality.

6.2 Migration & Travel

• Labor migration from endemic to non‑endemic areas can introduce parasites to new regions.
• Refugee camps often lack adequate water‑sanitation, creating local transmission hotspots.

6.3 Water‑Resource Management (Paper 2 – Water Resources)

• Irrigation schemes (e.g., sugar‑cane farms, vegetable plots) create artificial breeding habitats.
• Dam projects – case study: the **Kariba Dam** (Zambia/Zimbabwe) increased shoreline wetlands, leading to a measurable rise in malaria incidence in adjacent villages.
• Improved drainage, water‑storage design and community‑led maintenance reduce vector habitats – a **challenge & opportunity** for sustainable development.

6.4 Urbanisation & “Urban Malaria”

• Peri‑urban settlements often lack proper drainage; stagnant water in open drains supports mosquito breeding.
• Urban heat‑island effect raises local temperatures, subtly accelerating mosquito development.
• Example: informal settlements in **Nairobi, Kenya** and **Lagos, Nigeria** show higher malaria rates than surrounding suburban areas despite overall urban infrastructure.

7. Key Risk Factors (Geographically Structured)

1. Environmental Factors
   • Presence of standing water (hydrology).
   • Warm, humid climate (atmosphere).
   • Deforestation and land‑use change that alter vector habitats.
2. Socio‑Economic Factors
   • Poverty limits access to insecticide‑treated nets (ITNs) and indoor residual spraying (IRS).
   • Weak health‑care infrastructure delays diagnosis and treatment.
   • Low literacy reduces awareness of preventive measures.
3. Human Behaviour
   • Evening outdoor activities increase exposure to biting mosquitoes.
   • Inadequate use of protective clothing, repellents or nets.
   • Migration patterns moving infected individuals into susceptible communities.
4. Biological Factors
   • Drug resistance in Plasmodium falciparum.
   • Insecticide resistance in vector populations.
   • Genetic traits (e.g., sickle‑cell trait) that affect susceptibility and shape disease geography.

8. Impacts of High Malaria Prevalence (Linking Key Concepts)

9. Control Strategies – Connecting Risk Factors to Intervention (AO3 Evaluation)

1. Environmental Management – drainage of stagnant water, larviciding, and land‑use planning to reduce breeding sites.
2. Vector Control – distribution of ITNs, indoor residual spraying, house‑screening and community‑led source reduction.
3. Health‑System Strengthening – rapid diagnostic testing, prompt artemisinin‑based combination therapy (ACT), surveillance of drug/insecticide resistance.
4. Community Education – behaviour‑change campaigns on net use, protective clothing, and early treatment seeking.
5. Policy, Governance & International Aid – integration of malaria control into SDG 3 (Good Health) and SDG 6 (Clean Water & Sanitation); coordination between ministries of health, environment and agriculture; role of WHO, Global Fund and regional initiatives.

10. Climate‑Change Impacts & Governance (Paper 4 – Global Themes)

• Projected Changes
  • Rising temperatures expand the thermal envelope northwards and to higher altitudes.
  • Changes in rainfall patterns alter the availability of breeding sites – more intense storms can create temporary pools; prolonged droughts may concentrate people around limited water sources, increasing exposure.
• Governance Challenges
  • Need for adaptive surveillance systems that can respond to shifting risk zones.
  • Cross‑sectoral policies that align climate‑adaptation plans with malaria‑control programmes.
  • Ensuring equitable access to interventions for climate‑vulnerable populations.

11. Case‑Study Data Set (AO2 & AO3 Practice)

Fictional district of Lukasa (2022). Analyse the relationship between ITN coverage and malaria incidence, then evaluate the effectiveness of the ITN programme.

Suggested analysis: plot ITN coverage against incidence, discuss the inverse relationship, consider confounding variables (e.g., proximity to water bodies, socio‑economic status), and evaluate whether increasing net coverage alone would meet the district’s reduction target.

12. Mapping Key Geographical Concepts to Malaria

• Scale – micro‑habitat (breeding site) → district → regional (sub‑Saharan Africa) → global burden.
• Spatial Variation – clustering in low‑lying, humid zones; gaps in arid or high‑altitude areas.
• Change Over Time – trends linked to climate change, urban expansion, and intervention programmes.
• Place – soil type, vegetation, land‑use and infrastructure that create high‑risk locations.
• Cause‑Effect – temperature and water availability affect mosquito life cycles and parasite development.
• Systems – interaction of vector, parasite, human host and environment.
• Environmental Interaction – agricultural practices, dam construction and irrigation influencing vector habitats.
• Challenges & Opportunities – balancing development (irrigation, urban growth) with disease control.
• Diversity & Equality – disproportionate impact on low‑income and marginalised groups.

13. Evaluation of Control Measures (AO3 Checklist)

1. Effectiveness – reduction in incidence, mortality and morbidity.
2. Cost‑effectiveness – per‑person cost of ITNs, IRS, larviciding versus health‑system savings.
3. Sustainability – durability of nets, community ownership, resistance management.
4. Equity – reach to poorest, remote and conflict‑affected populations.
5. Unintended Consequences – insecticide resistance, ecological impacts of chemical larvicides, behavioural adaptation of vectors.
6. Governance – coordination between health, environment and development ministries; role of international donors.

14. Suggested Diagram