Define malaria.
Malaria is a parasitic infection caused by protozoa of the genus Plasmodium. Five species are known to infect humans; Plasmodium falciparum is the most life-threatening
What is the aetiology/pathophysiology of malaria?
Plasmodium transmitted through female Anopheles mosquitoes: Plasmodium: falciparum (most common), vivax, ovale, malariae, and knowlesi.
- The life cycle of malaria is dependent on both humans and mosquitoes. Sporozoites are transferred to a human host during blood meal.
- These travel to the liver for maturation → schizonts containing ~30 000 merozoite offspring.
- If a dormant stage exists (vivax, ovale), and is inadequately treated, merozoites can be released from the liver weeks, months, or years later causing recurrent disease.
- The rupture of schizonts releases merozoites which enter RBCs . In the RBC, merozoites form larger trophozoites and erthrocytic schizonts (poor prognostic indicator if seen on blood film).
- The rupture of erthrocytic schizonts produces the clinical manifestations of malaria.
What is the mode of transmission of malaria?
- Plasmodium species transmitted to humans through a female Anopheles mosquito bite
- Blood transfusion
- Organ transplantation
How common is Malaria?
- 438 000 deaths per year worldwide (most <5yrs)
- Most common tropical disease imported into UK, ~2000 cases/yr.
- ~20% fever in travellers from Africa presenting to UK hospitals is due to malaria.
What investigations would you do for malaria?
- Giemsa-stained thick and thin blood smear - parasite may be seen inside erythrocytes
- Thick - shows that parasites are present
- Thin - identifies species
- Rapid diagnostic tests (RDT) - detects parasite antigen or enzymes after 15 mins –> positive band on immunochromatographic test. Used out of hours.
If negative, repeat at 12-24hrs and again. In pregnancy thick films can be negative despite parasites in the placenta.
Other:
- FBC - thrombocytpenia, anaemia, variable WCC
- PT - may be prolonged, clotting -> DIC
- Glucose - hypo or hyperglycaemia
- ABG/lactate - acidosis
- Urinalysis - haemoglobinuria
- Serum electrolytes, urea, creatinine -AKI
- LFTs - elevated bilirubin or aminotransferases (ALT, AST)
- PCR blood for malaria
What are the risk factors for malaria?
- travel to endemic area
- inadequate or absent chemoprophylaxis - incidence of Plasmodium falciparum malaria in travellers who do not take prophylactic drugs is highest in West Africa
- insecticide-treated bed net not used in endemic area
- low host immunity
- pregnancy
- age <5years
- immunocompromise
- older age
What is the typical presentation of malaria?
P.falciparum usually incubates for 6 days and presents within 3 months of return from endemic area
- Fever - cyclical or continuous with spikes from rupture of infected RBCs
- Malaria paroxysms - chills, high fever, sweats
- Headache, malaise, myalgia
- Diarrhoea
- Cough
Severe disease:
- Jaundice
- Altered GCS
- Respiratory distress or ARDS
- Seizures
- Circulatory collapse
- Metabolic acidosis
- Renal failure (blackwater fever)
- Hepatic failure
- Severe anaemia or intravascular haemolysis
- Hypoglycaemia
How is malaria treated?
Artemisinin combination therapies (ACT) achieve rapid clearance of parasites by combined action at different stages of the parasite cycle.
- Artemether-lumefantrine: 4 tablets at 0, 4, 8, 24, 36, 48, and 60h.
- Dihydroartemisinin (DHA)-piperaquine: 4 tablets OD for 3d (if weight >60kg).
Resistance to ACT is emerging in Asia. Chloroquine is used for non-falciparum disease.
ABCDE
Resuscitate - correct hypoglycaemia, careful hydration, organ support as necessary
Daily parasitaemia checks
Non-falciparum: chloroquine + primaquine (check G6PD)
Falciparum:
Mild: Riamet (artemether-lumefantrine) OR malarone
Severe: IV Artesunate (1st choice) OR quinine
What is a schizont on a blood film indicative of?
Even one indicates severe malaria
NB: Schizont is a cell with multiple parasites which could burst and cause a rapid rise in parasitaemia
At what % parasitaemia should you treat?
2%
What is a mild falciparum malaria?
Not vomiting
Parasitaemia <2%
Ambulant
→ Artemisinin combination therapy (ACT), 4 tablets daily with food for three days
ACT regimens:
- E.g Riamet/ Co-artem – Artemisinin & Lumefantrine,
- Oral quinine 600mg tds (salt)
- then doxycycline 100mg od for 1 week
What is a side effect of artesunate and quinine?
Artesunate - delayed haemolysis
Quinine - cinchonism (indigestion causing toxicity), arrhythmias, hyperinsulinaemia
What are some prevention strategies against malaria?
- Repellent - 50% DEET
- Nets
- Prophylaxis - malorone, mefloquine, doxycycline e.g. doxycycline is taken 1-2 days before travel, during travel daily and for 4 weeks after leaving endemic area.
What are the complications of malaria?
- AKI
- Hypoglycaemia
- Metabolic acidosis
- Severe anaemia
- DIC
- Blackwater fever
- Septicaemia
- Seizures or other CNS
- ARDS
What is blackwater fever?
Intravascular haemolysis causing haemoglobinuria
What is the prognosis with malaria?
Children <5yrs most vulnerable
Mortality in non-immune travellers due to falciparum is 0.4-10%
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