Introduction
Malaria is a serious and potentially life-threatening infectious disease caused by Plasmodium parasites. It spreads through the bite of an infected female Anopheles mosquito. Malaria is very common in tropical regions and is one of the most important parasitic diseases worldwide. Any traveller returning from an endemic area with fever should always be checked for malaria, even if they took preventive medicine.
Plasmodium Species Causing Malaria
- P. falciparum – causes most severe disease; common in Africa
- P. vivax – common in Asia, Latin America; has dormant liver stage (relapse)
- P. ovale – similar to P. vivax; causes relapses
- P. malariae – chronic, low-grade infection
- P. knowlesi – zoonotic malaria from monkeys; found in Southeast Asia
Epidemiology
Malaria is endemic in most tropical areas — Asia, Africa, Latin America and Western Pacific. P. falciparum is responsible for most deaths, especially in sub-Saharan Africa. Worldwide, around 300–500 million cases occur yearly, leading to 1–3 million deaths. Both men and women are equally affected.
Aetiology
Humans get malaria when an infected Anopheles mosquito injects Plasmodium sporozoites during a blood meal. Different Plasmodium species have different incubation periods and clinical behaviours.
- P. falciparum: incubation 7–30 days; no dormant liver stage; most severe.
- P. vivax: incubation ~2 weeks; has dormant hypnozoites → relapse after months or years.
- P. ovale: incubation ~2 weeks; also causes relapses.
- P. malariae: incubation ~18 days; can cause lifelong chronic low-grade infection.
- P. knowlesi: incubation 3–27 days; rapid disease progression.
Life Cycle of Plasmodium
The parasite needs two hosts (mosquito & human) and has three major cycles:
- Sporogonic Cycle – sexual cycle inside the mosquito.
- Exo-erythrocytic Cycle – asexual cycle in liver cells.
- Erythrocytic Cycle – asexual cycle in RBCs.
1. Sporogonic Cycle (In Mosquito)
- Mosquito ingests gametocytes from infected human blood.
- Male & female gametes fuse into zygotes → ookinetes.
- Ookinetes penetrate mosquito gut wall → oocysts.
- Oocysts rupture releasing thousands of sporozoites.
- Sporozoites migrate to salivary glands → ready to infect humans.
2. Exo-erythrocytic (Liver) Cycle
- Human gets infected when bitten by mosquito carrying sporozoites.
- Sporozoites reach liver and infect hepatocytes.
- Inside liver, they multiply into schizonts → release merozoites into blood.
- P. vivax and P. ovale form dormant hypnozoites → relapses.
3. Erythrocytic (Blood) Cycle
- Merozoites infect RBCs → form ring-stage trophozoites.
- Trophozoites grow → schizonts → rupture RBCs releasing new merozoites.
- This cycle causes fever and anaemia.
- Some parasites form gametocytes → taken up by mosquito → restart cycle.
Pathophysiology
Malaria causes:
- Fever due to synchronous rupture of RBCs.
- Anaemia from destruction of red blood cells.
- Organ dysfunction due to parasite-infected RBCs sticking to small blood vessels → blockages, micro-infarcts, capillary leakage.
The severity depends on parasite species, parasite load and patient factors.
Clinical Manifestations
Common Symptoms
- Fever with chills, rigors and sweating
- Headache
- Fatigue, body pains
- Nausea, vomiting, diarrhoea
- Loss of appetite
- Confusion (in severe cases)
Physical Signs
- Pallor (anaemia)
- Jaundice due to RBC destruction
- Enlarged spleen (splenomegaly)
Manifestations of Severe Malaria
- Cerebral malaria – seizures, low consciousness
- Acute kidney injury – reduced urine output
- Metabolic acidosis – fast breathing
- Hypoglycaemia – sweating, confusion, seizures
- Respiratory distress – ARDS
- Severe anaemia
- DIC – bleeding tendency
- Shock – low BP
- Parasitaemia ≥2% or marked schizonts
Blackwater Fever
Severe haemolysis leads to dark red urine (haemoglobinuria) — a serious complication, mostly linked with P. falciparum.
Diagnosis
Diagnosis includes:
- Patient history (travel to endemic area)
- Enlarged spleen
- Low platelet count
- Increased bilirubin
- Blood smear (thick & thin smear) – gold standard
- Buffy coat test (non-specific)
- Rapid antigen tests (RDTs)
- PCR tests (highly specific)
Prevention
- Use mosquito nets, repellents, coils and sprays
- Wear long-sleeved clothing
- Drain stagnant water around home
- Government spraying and community mosquito control
- Antimalarial prophylaxis for travellers to endemic areas
Treatment
Commonly used medicines include:
- Antiprotozoals: Chloroquine, Mefloquine
- Antibiotics/Combinations: Doxycycline, Atovaquone + Proguanil, Amodiaquine, Lumefantrine, Sulfadoxine-Pyrimethamine
- Artemisinin combinations (ACT): Artemisinin + Piperaquine, Artemether + Lumefantrine
- Pregnancy: Quinine + Clindamycin or artemisinin combinations (as per guidelines)
Detailed Notes:
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