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
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
- 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
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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
- Recent foreign travel (90%): Falciparum malaria is most likely to occur within 3 months of return from an endemic area. The incubation period for malaria is at least 6 days. Malaria caused by other species may present more than a year after return from an endemic area.
- Fever (80%)
- Lethargy (60%)
- Sweating (35%)
- Myalgia (30%)
- Anorexia (30%)
- Headache (25%)
- Acute confusion (15%)
- Jaundice (10%)
- Impaired renal function (8%)
Signs
- Splenomegaly (15%)
- Hepatomegaly (10%)
- Hypotension (5%)
Investigations
- anaemia" class="int-link topic-link" >Anaemia (50%)
- Hyponatraemia (45%)
- Thrombocytopenia (25%)
- Abnormal LFTs (20%)
- Hypoglycaemia (10%)
- Anaemia (8%)
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
Other tests
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
Feature of severe malaria
Severe 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)