Malaria is a potentially life-threatening parasitic disease caused by Plasmodium species. It spreads to humans through the bite of an infected female Anopheles mosquito. Malaria is common in tropical countries. Fever in a person returning from a malaria-endemic area should always be treated as possible malaria, even if they were taking preventive medicines.
Five species of Plasmodium infect humans:
- P. falciparum – most dangerous; causes severe and fatal malaria
- P. vivax – common in Asia; can relapse from liver
- P. ovale – has dormant liver stage; causes relapses
- P. malariae – low-grade chronic infection
- P. knowlesi – zoonotic malaria; rapid daily fevers, can be fatal
Aetiology
Malaria is caused by Plasmodium protozoa, which are transmitted to humans during a mosquito blood meal. The parasite is present in mosquito saliva and enters the bloodstream when the mosquito bites.
Life Cycle & Pathophysiology (Simplified)
The Plasmodium lifecycle involves two hosts — humans and mosquitoes — and three major stages:
- Sporogonic cycle (mosquito) – sexual reproduction
- Exo-erythrocytic cycle (human liver) – asexual multiplication
- Erythrocytic cycle (human red blood cells) – asexual multiplication causing symptoms
1. Sporogonic Cycle (Mosquito)
- Mosquito ingests male and female gametocytes during a blood meal.
- Gametes fuse → zygote → ookinete → oocyst.
- Oocyst bursts, releasing sporozoites that move to the mosquito’s salivary glands.
- These sporozoites are then injected into a human during the next bite.
2. Exo-erythrocytic Cycle (Human Liver)
- Sporozoites travel to liver cells and multiply into thousands of merozoites.
- P. vivax and P. ovale can form dormant liver forms (hypnozoites), causing relapse months or years later.
3. Erythrocytic Cycle (Human Blood)
- Merozoites infect red blood cells, multiply and burst the cells.
- This rupture releases more merozoites → cycles repeat.
- RBC rupture causes fever patterns:
- 48-hour cycle – P. vivax, P. ovale, P. falciparum
- 72-hour cycle – P. malariae
- 24-hour cycle – P. knowlesi
- Some merozoites become gametocytes, which infect mosquitoes.
Clinical Manifestations
Common Symptoms
- Fever with chills and rigors (may be continuous or periodic)
- Sweating
- Severe tiredness and malaise
- Headache
- Nausea, vomiting, diarrhoea
- Muscle and joint pain
- Cough, sore throat
- Confusion (especially in severe malaria)
Physical Signs
- Anaemia (pallor)
- Jaundice (due to destruction of RBCs)
- Splenomegaly (enlarged spleen)
Manifestations of Severe Malaria
Most severe malaria cases are caused by P. falciparum. Severe malaria needs immediate hospital care.
- Cerebral malaria – seizures, altered consciousness
- Acute kidney injury
- Metabolic acidosis (breathing fast, altered mental state)
- Hypoglycaemia (confusion, sweating, seizures)
- Acute respiratory distress syndrome (respiratory failure)
- Severe anaemia
- Bleeding tendency or DIC
- Shock (BP < 90/60 mmHg)
- High parasite load (≥2% parasitaemia)
Blackwater Fever
A severe form of malaria where massive RBC destruction causes dark red or black urine due to hemoglobin in urine (haemoglobinuria). It is a medical emergency.
Diagnosis
Diagnosis is based on symptoms, travel history and laboratory tests.
Major Diagnostic Methods
- Blood smear (thick & thin film) – gold standard; identifies species and parasite load
- Rapid antigen tests – quick screening
- PCR – very accurate but expensive
- Blood tests – low platelets, high bilirubin
- Enlarged spleen on physical examination
Prevention
Personal Protection
- Use mosquito nets (preferably insecticide-treated)
- Use mosquito repellents, creams and sprays
- Wear full-sleeve clothing during evening and night
- Avoid areas with stagnant water around the home
Community Measures
- Spraying insecticides in mosquito-breeding areas
- Covering open drains
- Proper garbage disposal
- Public health education campaigns
Chemoprophylaxis
Travellers to endemic areas may need antimalarial prophylaxis.
Examples include:
- Mefloquine
- Doxycycline
- Atovaquone-proguanil
Treatment
Antiprotozoal Drugs
- Chloroquine – effective in chloroquine-sensitive regions
- Mefloquine
- Quinine (with clindamycin in pregnancy)
- Artemisinin derivatives (e.g., artesunate, artemether)
- Doxycycline
- Atovaquone + Proguanil
- Amodiaquine, lumefantrine, sulfadoxine + pyrimethamine
- Artemisinin-based combination therapies (ACTs) – mainstay for falciparum malaria
Treatment Notes
- P. vivax and P. ovale require primaquine to kill dormant liver stages (hypnozoites).
- Pregnant women: quinine + clindamycin or approved artemisinin combinations.
- Severe malaria requires IV artesunate.
Detailed Notes:
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