Malaria — Symptoms, Causes & Treatment | MyMedicPlus

Malaria is a potentially life-threatening parasitic disease caused by five Plasmodium species, transmitted exclusively through the bite of infected female Anopheles mosquitoes, which feed primarily between dusk and dawn. The five species are: P. falciparum (responsible for the most severe disease and the majority of global mortality), P. vivax (most geographically widespread, capable of forming dormant liver hypnozoites causing relapse months to years later), P. malariae (causes mild chronic infection), P. ovale (two subspecies, also forms hypnozoites and causes relapse), and P. knowlesi (a zoonosis from macaques in Southeast Asia that can cause severe disease). According to the WHO World Malaria Report 2023, there were 249 million malaria cases and 608,000 deaths in 2022, with sub-Saharan Africa accounting for 93% of all cases and 95% of deaths; children under 5 years represent approximately 76% of all malaria deaths. The parasitic life cycle alternates between the Anopheles mosquito host (sexual cycle producing sporozoites injected into humans) and the human host (asexual cycle in hepatocytes followed by cyclical erythrocytic schizogony releasing merozoites). P. falciparum-infected red blood cells sequester in microvascular beds via cytoadherence to endothelial receptors, causing the microvascular obstruction responsible for cerebral malaria and other severe manifestations.

Malaria transmission occurs exclusively through the bite of infected female Anopheles mosquitoes feeding between dusk and dawn; the sporozoites injected during the blood meal migrate to the liver within minutes, beginning the hepatic schizogony stage. Risk is highest in sub-Saharan Africa, South Asia (India, Pakistan, Bangladesh), Southeast Asia, Papua New Guinea, and parts of Latin America. Key risk factors for infection and severity: travel to or residence in endemic areas without adequate prophylaxis; children under 5 years (lack of acquired immunity, highest mortality group); pregnant women (immune modulation enables placental sequestration, causing maternal anaemia, intrauterine growth restriction, and low birth weight); first-time travellers (non-immune adults with no prior exposure); HIV-infected and otherwise immunocompromised individuals; people with asplenia (impaired clearance of parasitised erythrocytes causes overwhelming severe malaria); and sickle cell trait (provides partial protection against P. falciparum — a key evolutionary pressure). Transmission is seasonal in many regions, peaking during and after rainy seasons when mosquito breeding sites expand. Drug resistance, particularly P. falciparum resistance to chloroquine (nearly universal) and emerging artemisinin partial resistance in the Greater Mekong subregion and eastern Africa, is a critical public health concern.

The classic malaria attack follows three stages: cold stage (sudden onset rigors with intense shivering lasting 15-60 minutes), hot stage (high fever 39-41°C with severe headache, myalgia, arthralgia, nausea, vomiting, and sometimes delirium, lasting 2-6 hours), and sweating stage (profuse sweating with resolution of fever and temporary relief). In P. falciparum malaria, fever is often irregular and non-cyclical; in P. vivax and P. ovale, classic tertian fever (48-hour cycles) occurs; in P. malariae, quartan fever cycles every 72 hours. Incubation period: P. falciparum 7-14 days (rarely over 1 month, though inadequate prophylaxis can delay onset by months); P. vivax and P. ovale 12-17 days (with relapses possible 6-24 months later from dormant hypnozoites); P. malariae 18-40 days. Severe P. falciparum malaria (WHO criteria) — defined by any of: impaired consciousness or unarousable coma (cerebral malaria); severe anaemia (haemoglobin below 70 g/L); respiratory distress with pulmonary oedema or ARDS; hypoglycaemia (blood glucose below 2.2 mmol/L); circulatory collapse or shock; abnormal bleeding; hyperparasitaemia (over 10% infected RBCs); jaundice with evidence of vital organ dysfunction; or acute kidney injury — carries 15-25% mortality even with treatment. Splenomegaly is a characteristic clinical sign of repeated malaria exposure.

Blood film microscopy — examining Giemsa-stained thick and thin blood films under light microscopy — remains the gold standard, providing species identification, parasite density quantification (percent parasitaemia), and detection of sexual stages (gametocytes). Thick films concentrate parasites for high sensitivity; thin films allow species-specific morphological identification based on red cell characteristics, parasite size, and malarial pigment appearance. Sensitivity is examiner-dependent and degrades with low parasitaemia. Rapid diagnostic tests (RDTs) detect specific Plasmodium antigens in 15-20 minutes using finger-prick capillary blood: HRP2 for P. falciparum (highly specific and sensitive but false-positive results persist weeks after parasite clearance), pLDH and aldolase for pan-malaria detection and species differentiation. RDTs are WHO-recommended first-line diagnostics in sub-Saharan Africa. PCR-based malaria testing (nested PCR, real-time PCR) achieves the highest sensitivity and specificity, detecting as few as 1-5 parasites/μL blood and providing definitive species differentiation — recommended for low-parasitaemia cases, mixed infections, travel medicine assessment, and monitoring treatment response. In the UK and other non-endemic countries, all returned travellers with fever should have urgent blood films, RDT, and PCR; three negative films taken 12-24 hours apart are required to exclude malaria. Additional investigations in severe malaria: FBC, renal function, glucose, lactate, blood cultures, chest X-ray, and lumbar puncture to exclude bacterial meningitis.

Uncomplicated P. falciparum malaria: artemisinin-based combination therapy (ACT) is WHO-recommended first-line treatment for all regions. Artemether-lumefantrine (Coartem, 6-dose regimen over 3 days) is widely used in Africa; artesunate-amodiaquine, artesunate-mefloquine, artesunate-pyronaridine, and dihydroartemisinin-piperaquine are alternatives depending on regional resistance patterns and availability. Artemisinin acts rapidly, reducing parasite biomass by >99% within 48 hours. ACT adherence requires completing the full course. In regions of emerging artemisinin partial resistance (Greater Mekong subregion, Rwanda, Uganda — pfkelch13 mutations), alternative partner drug regimens or triple ACT may be required. Severe P. falciparum malaria: intravenous (IV) artesunate is the treatment of choice, superior to IV quinine in the AQUAMAT and SEAQUAMAT trials — reducing mortality by 22-34%; after IV artesunate, a full oral ACT course must complete treatment. Adjunctive measures for severe malaria include: exchange transfusion for hyperparasitaemia over 10% (controversial), IV dextrose for hypoglycaemia, cooling for high fever, anticonvulsants for seizures (IV lorazepam or artesunate — avoid phenobarbitone which worsens coma), and careful fluid management to prevent pulmonary oedema. P. vivax and P. ovale (radical cure): chloroquine (where sensitive) plus primaquine 15mg daily for 14 days — G6PD testing is mandatory before primaquine as haemolysis in G6PD-deficient patients is severe; tafenoquine is an alternative single-dose option for P. vivax relapse prevention. Malaria in pregnancy: oral quinine plus clindamycin in the first trimester; ACT is preferred in second and third trimesters. IV artesunate for severe malaria in pregnancy regardless of trimester.

Cerebral malaria is the most feared complication of P. falciparum, causing unarousable coma (Blantyre coma score ≤2), seizures, and herniation — mortality is 15-25% even with optimal IV artesunate treatment; 10-20% of survivors have persistent neurological sequelae including cognitive impairment, epilepsy, hemiplegia, and developmental delay in children. Severe malarial anaemia (haemoglobin below 50 g/L) from haemolysis and dyserythropoiesis requires blood transfusion and is a leading cause of malaria mortality in children under 5. Acute respiratory distress syndrome (ARDS) and non-cardiogenic pulmonary oedema from microvascular injury carry a 70-80% mortality in adults with severe malaria. Acute kidney injury requiring renal replacement therapy occurs in 25-30% of severe malaria cases in adults. Blackwater fever — massive intravascular haemolysis causing dark 'Coca-Cola' haemoglobinuria — is associated with recurrent falciparum infection and historical quinine use. Hypoglycaemia from parasite glucose consumption, impaired gluconeogenesis, and quinine-stimulated insulin release is common and rapidly fatal without IV dextrose. Splenic rupture is rare but life-threatening. Recurrent P. vivax and P. ovale relapses from dormant liver hypnozoites cause repeated debilitating illness and contribute to chronic anaemia and malnutrition if primaquine radical cure is not administered.

Malaria chemoprophylaxis is mandatory for all non-immune travellers to endemic areas and must be tailored to destination, local resistance patterns, trip duration, and individual medical history. Atovaquone-proguanil (Malarone) — started 1-2 days before, taken daily during, and for 7 days after travel — is highly effective, well-tolerated, and recommended for most destinations including chloroquine-resistant Africa; doxycycline 100mg daily is a cheaper alternative, started 1-2 days before and continued 4 weeks after travel, also providing protection against leptospirosis and rickettsial diseases; mefloquine (Lariam) 250mg weekly is effective but requires 2-3 weeks of pre-travel dosing and is contraindicated in neuropsychiatric disorders. Personal protective measures are essential regardless of prophylaxis: WHO-recommended long-lasting insecticidal nets (LLINs, impregnated with deltamethrin or permethrin) reduce P. falciparum transmission by 50-80% in high-burden settings; indoor residual spraying (IRS) with insecticides; permethrin-treated clothing; and DEET-based repellents (20-50% concentration) applied to exposed skin. The RTS,S/AS01E malaria vaccine (Mosquirix, WHO recommended 2021) — targeting the P. falciparum circumsporozoite protein — reduces clinical malaria by 39% and severe malaria by 29% in children aged 5-17 months in the fourth dose 2-year schedule; the R21/Matrix-M vaccine (Oxford-Serum Institute) demonstrated 77% efficacy in Phase 3 trials. Intermittent preventive treatment in pregnancy (IPTp) with sulfadoxine-pyrimethamine reduces maternal anaemia and placental malaria. Seasonal malaria chemoprevention (SMC) with sulfadoxine-pyrimethamine plus amodiaquine in children under 5 in the Sahel substantially reduces under-5 malaria mortality.

Any traveller or recent returnee from a malaria-endemic region (sub-Saharan Africa, South or Southeast Asia, Latin America) who develops fever, chills, rigors, headache, or muscle aches within 30 days of return must seek urgent medical assessment on the same day — malaria can progress from mild to life-threatening within 24-48 hours. Do not wait and see if symptoms improve. Tell the doctor about your travel history immediately. Go directly to an emergency department (A&E) if you have: fever with confusion, drowsiness, severe headache, difficulty breathing, dark urine (blackwater fever), jaundice, or seizures — these are signs of severe falciparum malaria, which is a medical emergency requiring IV artesunate. Pregnant women with fever returning from endemic areas require emergency evaluation as malaria in pregnancy is particularly dangerous. Returning travellers should specifically request malaria testing (thick and thin blood film microscopy plus RDT) — routine infection screen without specifically mentioning travel may miss malaria.