Introduction

Falciparum malaria is the commonest, and most severe, type of malaria.

Epidemiology

  • Incidence: 2.10 cases per 100,000 person-years
  • Peak incidence: 40-50 years
  • Sex ratio: more common in males 1.5:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

The protection from malaria that sickle-cell trait offers is well documented. Other protective factors include
  • G6PD deficiency
  • HLA-B53
  • absence of Duffy antigens

Pathophysiology

Key points
  • following inoculation parasites (termed sporozoites) pass to the liver
  • in the liver they divide asexually over around 10 days, maturing into schizonts, following which they emerge from the liver (as merozoites) and infect red blood cells, appearing as tiny rings
  • as the parasites mature the infected red blood cells are sequestered by various tissues of the body
  • Plasmodium vivax and Plasmodium ovale (but not Plasmodium falciparum) lay down hypnozoites in the liver
  • these dormant forms are not affected by conventional antimalarial drugs and can hence reactivate after months or years

An illustration of the life cycle of the malaria parasite. Credit: NIAID

Although there is no hypnozoite stage in Falciparum, resurgences may occur due to asexual parasites resistant to quinine. Falciparum may be resistant to pyrimethamine + sulfadoxine (Fansidar) therefore doxycycline is often given

Clinical features

Symptoms
Investigations

Investigations

The gold standard for diagnosis of malaria remains the blood film. Rapid diagnostic tests (detecting plasmodial histidine-rich protein 2) are currently being trialled and have shown sensitivities from 77-99% and specificities from 83-98% for falciparum malaria

Blood film - if doubt about diagnosis should be repeated
  • thick: more sensitive
  • thin: determine species

Other tests
  • thrombocythaemia is characteristic
  • normochromic normocytic anaemia" class="int-link topic-link" >anaemia
  • normal white cell count
  • reticulocytosis

Management

Uncomplicated falciparum malaria
  • strains resistant to chloroquine are prevalent in certain areas of Asia and Africa
  • the 2010 WHO guidelines recommend artemisinin-based combination therapies (ACTs) as first-line therapy
  • examples include artemether plus lumefantrine, artesunate plus amodiaquine, artesunate plus mefloquine, artesunate plus sulfadoxine-pyrimethamine, dihydroartemisinin plus piperaquine

Feature of severe malaria
  • schizonts on a blood film
  • parasitaemia > 2%
  • hypoglycaemia
  • acidosis
  • temperature > 39 °C
  • severe anaemia" class="int-link topic-link" >anaemia
  • complications as below

Severe falciparum malaria
  • a parasite counts of more than 2% will usually need parenteral treatment irrespective of clinical state
  • intravenous artesunate is now recommended by WHO in preference to intravenous quinine
  • if parasite count > 10% then exchange transfusion should be considered
  • shock may indicate coexistent bacterial septicaemia - malaria rarely causes haemodynamic collapse

Complications

Complications
  • cerebral malaria: seizures, coma
  • acute renal failure: blackwater fever, secondary to intravascular haemolysis, mechanism unknown
  • acute respiratory distress syndrome (ARDS)
  • hypoglycaemia
  • disseminated intravascular coagulation (DIC)