Malaria: Epidemiology, Prevention, and Control

1. Global Burden and Epidemiology

• 2024 global malaria funding of US$3.9 billion fell far short of the Global Technical Strategy target of US$9.3 billion
• Progress in malaria mortality reduction between 2000–2015 has reversed since then; estimated case numbers are rising
• An increasing number of low-transmission countries are now targeting elimination — but this is threatened by drug and insecticide resistance
• ~54 million children received seasonal malaria chemoprevention (SMC) across 19 countries in 2024

2. Causative Agents and Transmission

3. Life Cycle

1. Sporozoites injected into bloodstream during mosquito bite → travel to liver
2. Hepatic (pre-erythrocytic) stage: Sporozoites bind to hepatocyte proteoglycans via thrombospondin-related adhesive protein and circumsporozoite protein → differentiate into merozoites (clinically silent; 1–4 weeks)
3. Erythrocytic stage: Merozoites bind glycophorin (via lectin-like molecule) → enter RBCs → become ring trophozoites → schizonts → merozoites → lysis of RBC → clinical disease
4. P. falciparum schizonts express PfEMP1 on RBC surface (knobs) → bind ICAM-1, VCAM-1, CD36 on microvascular endothelium → sequestration in capillary beds → cerebral and organ-specific pathology
5. Some trophozoites → gametocytes → taken up by mosquito → sexual reproduction → new sporozoites

4. High-Risk Groups

• Children <5 years — most deaths
• Pregnant women (especially primigravidae) — risk of severe disease, spontaneous abortion, stillbirth, low birth weight
• Non-immune travelers to endemic areas — most fatalities in developed world are from delayed diagnosis
• Immunocompromised persons (including HIV+)
• Blood transfusion recipients / IV drug users (uncommon)

5. Clinical Features (Brief)

• Fever — classically periodic: daily (P. knowlesi), every 48 h (P. falciparum, vivax, ovale), every 72 h (P. malariae) — though unreliable in practice
• Severe malaria (mainly P. falciparum): cerebral malaria (coma), severe anemia, respiratory distress/ARDS, renal failure, thrombocytopenia, hypoglycemia, shock, >5% parasitemia
• Malaria has driven profound selective pressure on human genetics: sickle cell trait, G6PD deficiency, α-thalassemia, and pyruvate kinase deficiency are protective against severe malaria

6. Drug Resistance — Major Challenge

• Chloroquine resistance in P. falciparum spread globally from the 1960s; chloroquine-resistant P. vivax now reported in Indonesia, PNG, Myanmar, India, Guyana
• Artemisinin resistance (P. falciparum) emerged in SE Asia (late 2000s), now prevalent throughout the Greater Mekong Subregion, and has emerged and spread in East Africa — a critical threat
• Key resistance markers: Pfkelch13 mutations (artemisinin), Pfcrt (chloroquine), Pfmdr1 amplification (mefloquine)
• Falsified/substandard antimalarials in Asian and African markets are a major contributor to treatment failures

7. Diagnosis

• Gold standard: Thick and thin blood film microscopy — thick film for sensitivity (detects low parasitemia); thin film for species identification and parasite density
• If negative but malaria suspected: repeat every 12–24 hours for 72 hours (minimum 3 smears)
• Rapid Diagnostic Tests (RDTs): Detect specific malaria antigens; FDA-approved tests available; must be confirmed by microscopy
• PCR: Reference laboratory test; most useful for species confirmation; too slow for initial treatment decisions
• Serology: Generally not useful clinically; reserved for epidemiologic surveys

8. Treatment

• ACT = artemisinin derivative (artesunate, artemether, or dihydroartemisinin) + a partner drug in fixed-dose coformulation
• For P. knowlesi: ACT recommended
• For P. vivax, ovale, malariae: chloroquine (where sensitive) or ACT; add primaquine (after ruling out G6PD deficiency) to eliminate hypnozoites and prevent relapse

9. Prevention and Control

A. Vector Control

B. Personal Protection (Travelers and Endemic Populations)

• Avoid peak mosquito biting hours (dusk to dawn)
• Insect repellents: DEET 20–50% (preferred); 7% picaridin if DEET unacceptable; apply to all exposed skin
• Permethrin-treated clothing for added protection
• ITNs: Sleep under insecticide-impregnated bed nets if not in well-screened accommodation
• Protective clothing: Long-sleeved shirts and long trousers

C. Chemoprophylaxis (Travelers to Endemic Areas)

• Regimen choice depends on: travel itinerary (region, drug resistance pattern), medical history, pregnancy status, potential drug interactions
• Chemoprophylaxis is never 100% reliable — always consider malaria in febrile returned travelers even if taking prophylaxis

D. Preventive Treatment in Special Populations

• Sulfadoxine-pyrimethamine (SP) at each antenatal visit (maximum monthly) in 2nd and 3rd trimesters in high-transmission areas
• Coverage target: 80%; actual 2024 coverage: only 45% of eligible women received ≥3 doses
• Women on TMP-SMX for HIV prophylaxis should not receive SP concurrently

• Amodiaquine + SP given to children <5 years during high-transmission season in the Sahel
• ~54 million children reached across 19 countries in 2024

E. Vaccines

10. Elimination and Eradication Strategy (WHO GTS)

• 90% reduction in malaria case incidence and mortality rates vs. 2015
• Elimination in ≥35 countries by 2030
• Universal access to malaria prevention, diagnosis, and treatment

1. Antimalarial drug resistance (especially artemisinin resistance spreading to Africa)
2. Insecticide resistance in Anopheles vectors
3. Funding gaps (2024: $3.9B actual vs. $9.3B needed)
4. Climate change — may expand the geographic range of Anopheles mosquitoes
5. Inadequate health system infrastructure in high-burden countries

Sources

• Harrison's Principles of Internal Medicine, 22nd Edition (2025, McGraw Hill) — Chapters 130, 231
• Red Book 2021: Report of the Committee on Infectious Diseases (AAP)
• Robbins & Kumar Basic Pathology
• Murray & Nadel's Textbook of Respiratory Medicine
• WHO World Malaria Report 2025
• Medicines for Malaria Venture — Malaria Facts & Statistics 2025