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Malaria

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Overview

Malaria is a protozoan infection characterised by severe fatigue, paroxysms of high fever and sweating, and can cause anaemia. It is caused by four species of the Plasmodium genus and spread by female Anopheles (or Marsh) mosquitos:

  • Plasmodium falciparum – most common, causes nearly all episodes of severe malaria
  • Plasmodium vivax – the most common cause of non-falciparum malaria, tends to cause milder infection
  • Plasmodium ovale – also tends to cause milder infection
  • Plasmodium malariae – tends to cause milder infection and can cause chronic infection

The word malaria means ‘bad air’, associated with marshes where mosquitos breed.

Pathophysiology

Sporozoites are transmitted by Anopheles mosquito bites and travel through the blood to hepatocytes, where they mature into schizonts and release merozoites into the bloodstream. The merozoites invade red blood cells, mature into schizonts and rupture to release merozoites and the cycle repeats.

Plasmodium vivax and Plasmodium ovale can remain dormant for months in the liver by producing hypnozoites which can lead to relapses after the initial infection. Plasmodium falciparum does not produce hypnozoites and is not associated with relapse. Plasmodium malariae also does not produce hypnozoites but can persist in the blood for years.

Epidemiology

  • Malaria is the most common imported tropical disease in the UK
  • In 2019, 1719 cases were reported in the UK
  • Malaria is endemic in tropical parts of the world including Asia, Africa, Central and South America, and some Caribbean islands

Presentation

Overview

Malaria does not have specific symptoms and may be misdiagnosed. It should be suspected in someone who has travelled to an endemic area with a history of fever.

  • Most cases of falciparum malaria present within 2-3 months and nearly all within 6 months
  • Non-falciparum malaria may present after months-years due to the reactivation of hypnozoites

General features of malaria include:

  • High fever (often 39°C or higher), sweats, rigours
  • General features – headaches, myalgia, arthralgia
  • Lethargy, fatigue, somnolence
  • Reduced appetite, nausea, vomiting, jaundice, abdominal pain
  • Hepatomegaly and splenomegaly may be seen

Falciparum malaria

Falciparum malaria is the most severe type of malaria. Features include suggesting severe malaria include:

  • Cerebral involvement – reduced consciousness, seizures
  • Renal impairment – oliguria
  • Acidosis – may cause deep breathing
  • Hypoglycaemia – more common in pregnant people
  • Respiratory distress – pulmonary oedema or acute respiratory distress syndrome (ARDS) – more common in pregnant people
  • Severe anaemia
  • Haemorrhage – specifically disseminated intravascular coagulopathy
  • Shock
  • Sepsis – more common in pregnant people
  • Haemoglobinuria – falciparum malaria can cause severe haemolysis and dark red urine (also known as ‘blackwater fever’)
  • Parasitaemia (>10%.)
  • Schizonts on a blood film

Non-falciparum malaria

Plasmodium vivax is them most common cause of non-falciparum malaria. Features of non-falciparum malaria include:

  • The general features of malaria discussed above
  • Cyclical fever – paroxysms of fever based on the parasite’s lifecycle:
    • Plasmodium vivax and Plasmodium ovale – every 48 hours
    • Plasmodium malariae – every 72 hours

Investigations

  • Thick and thin blood films are the gold standard diagnostic test – identifies parasites
  • Full blood count (FBC) – may show anaemia and thrombocytopenia
  • Urea and electrolytes (U&Es) – severe infection can cause renal dysfunction
  • Liver function tests (LFTs) – unconjugated bilirubin due to haemolysis
  • Serum blood glucose – shows hypoglycaemia in severe disease
  • Arterial/venous blood gas – shows metabolic acidosis in severe disease

Management

Overview

For uncomplicated falciparum malaria, artemisinin-based combination therapies are first-line (e.g. artemether + lumefantrine), except in pregnant people. Since vivax and ovale malaria have a hypnozoite stage, they can relapse months after treatment.

In severe falciparum malaria, intravenous artesunate may be used. In more severe cases, exchange transfusion may be necessary.

Prognosis

  • If promptly diagnosed and treated before organ dysfunction develops, most people make a quick and complete recovery.
  • If untreated, severe and potentially life-threatening malaria can develop over hours to days.

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