Introduction
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
- G6PD deficiency
- HLA-B53
- absence of Duffy antigens
Pathophysiology
- 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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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
- 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%)
- Splenomegaly (15%)
- Hepatomegaly (10%)
- Hypotension (5%)
- anaemia" class="int-link topic-link" >Anaemia (50%)
- Hyponatraemia (45%)
- Thrombocytopenia (25%)
- Abnormal LFTs (20%)
- Hypoglycaemia (10%)
- Anaemia (8%)
Investigations
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
- 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
- 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)