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Malaria

Medicine > Infection

Background knowledge 🧠

Definition

  • Malaria is a mosquito-borne infectious disease caused by Plasmodium parasites.
  • It is transmitted to humans through the bites of infected female Anopheles mosquitoes.
  • Characterised by cycles of fever, chills, and anaemia.

Epidemiology

  • Endemic in tropical and subtropical regions, particularly Sub-Saharan Africa, Asia, and South America.
  • Estimated 229 million cases worldwide in 2019.
  • UK sees about 1,500 imported cases annually.
  • Highest risk among travellers returning from endemic areas.

Pathophysiology

  • Plasmodium parasites enter the bloodstream via mosquito bite.
  • Parasites travel to the liver, where they mature and multiply.
  • Infected liver cells burst, releasing parasites into the bloodstream.
  • Parasites invade red blood cells, leading to their destruction.
  • Cyclical rupture of red blood cells causes fever and other symptoms.
  • Severe cases can cause organ dysfunction and death.

Aetiology/Risk factors

  • Caused by Plasmodium species: P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi.
  • Transmitted by the bite of an infected female Anopheles mosquito.
  • Risk factors include: travel to endemic areas, lack of mosquito protection, and inadequate prophylaxis.
  • Children, pregnant women, and immunocompromised individuals are at higher risk.
  • Socioeconomic factors and poor access to healthcare increase risk.
  • Climate and environmental factors affect mosquito breeding and transmission.

Types

  • Plasmodium falciparum: Most severe, responsible for the majority of malaria deaths.
  • Plasmodium vivax: Causes recurring malaria due to dormant liver stage.
  • Plasmodium ovale: Similar to P. vivax, with relapses.
  • Plasmodium malariae: Can cause chronic infection, less severe.
  • Plasmodium knowlesi: Zoonotic malaria, found in Southeast Asia, can be severe.

Clinical Features 🌡️

Symptoms

  • Fever, chills, and sweating (often with a cyclical pattern).
  • Headache.
  • Nausea and vomiting.
  • Muscle pain and fatigue.
  • Anaemia and jaundice (due to red blood cell destruction).
  • Splenomegaly.
  • In severe cases: confusion, seizures, and respiratory distress.
  • Symptoms typically appear 10 days to 4 weeks after infection.

Signs

  • Fever, often with a periodic pattern (every 48-72 hours).
  • Pallor and jaundice due to haemolysis.
  • Tachycardia and hypotension.
  • Hepatosplenomegaly.
  • Altered mental state in severe cases (cerebral malaria).
  • Respiratory distress or ARDS in severe malaria.
  • Dark urine (haemoglobinuria) in severe haemolysis.
  • Signs of shock in severe cases.

Investigations 🧪

Initial tests

  • Blood film microscopy: gold standard for diagnosis, detects parasites in blood.
  • Rapid diagnostic tests (RDTs): for Plasmodium antigens.
  • Full blood count: anaemia, thrombocytopenia.
  • Liver function tests: elevated bilirubin, transaminases.
  • Renal function tests: creatinine, urea for renal impairment.
  • Blood glucose: hypoglycaemia in severe malaria.
  • Arterial blood gas: in severe cases, assess acidosis and respiratory function.
  • Coagulation profile: in severe cases, assess for DIC.

Diagnostic tests

  • Thick and thin blood films: parasite identification and quantification.
  • PCR: for species-specific diagnosis and in low-parasite-load cases.
  • Serology for past infection (not useful for acute diagnosis).
  • Repeat blood films every 12-24 hours if initial films are negative and clinical suspicion remains high.
  • Chest X-ray if respiratory symptoms are present.
  • ECG to monitor for QT prolongation if certain antimalarial drugs are used.
  • Lumbar puncture if meningitis is suspected in differential diagnosis.

Management 🥼

Management

  • Uncomplicated malaria: oral antimalarials such as artemisinin-based combination therapies (ACTs) or chloroquine (for sensitive strains).
  • Severe malaria: intravenous antimalarials such as artesunate or quinine.
  • Supportive care: IV fluids, blood transfusions, and management of complications (e.g., hypoglycaemia, renal failure).
  • Monitoring for drug resistance and adjusting treatment as necessary.
  • Prophylaxis for travellers to endemic areas: medications such as doxycycline, atovaquone-proguanil, or mefloquine.
  • Public health measures: vector control, insecticide-treated nets, and education.
  • Patient education on adherence to treatment and prevention of mosquito bites.
  • Refer to UK guidelines for specific treatment protocols.

Complications

  • Cerebral malaria: seizures, coma.
  • Severe anaemia (due to haemolysis).
  • Acute respiratory distress syndrome (ARDS).
  • Acute kidney injury.
  • Hypoglycaemia
  • Liver failure and jaundice.
  • Disseminated intravascular coagulation (DIC).
  • Splenic rupture.
  • Secondary bacterial infections.

Prognosis

  • Good prognosis with early diagnosis and appropriate treatment.
  • Delayed treatment can lead to severe complications and death.
  • Mortality highest in children and non-immune individuals.
  • Recurrence possible with P. vivax and P. ovale due to liver stages.
  • Regular follow-up to ensure clearance of the parasite and manage any complications.
  • Prevention and prophylaxis are key to reducing incidence and mortality.
  • Continued surveillance for drug resistance is crucial.

Key points

  • Malaria is a serious and potentially fatal disease caused by Plasmodium parasites.
  • Prompt diagnosis and treatment are essential for good outcomes.
  • Blood film microscopy remains the gold standard for diagnosis.
  • Antimalarial treatment should be based on the infecting species and severity of disease.
  • Preventive measures include prophylaxis for travelers and vector control.
  • Refer to UK guidelines for the latest management protocols.
  • Education on mosquito bite prevention is crucial.
  • Monitoring for drug resistance is important for effective treatment.

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Infection