Malaria

Question 1

Define malaria.

Answer 1

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

Question 2

What is the mode of transmission of malaria?

Answer 2

• Plasmodium species transmitted to humans through a female Anopheles mosquito bite
• Blood transfusion
• Organ transplantation

Question 3

What is the aetiology/pathophysiology of malaria?

Answer 3

Plasmodium transmitted through 5 out of 40 species of female Anopheles mosquitoes: Plasmodium falciparum (most common), Plasmodium vivax, Plasmodium ovale, Plasmodium malariae, and Plasmodium 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 via the blood-stream to the liver where maturation occurs to form 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.

Question 4

How common is Malaria?

Answer 4

• 214 million/cases per year with 438 000 deaths.
• Sub-Saharan Africa: 88% of malaria cases, 90% of deaths (most age <5yr).
• Most common tropical disease imported into uk, ~2000 cases/yr.
• ~20% fever in travellers from Africa presenting to UK hospitals is due to malaria.
• Preventable and treatable: incidence ↓ by 37% and deaths ↓ by 60% since 2000.

Question 5

What are the risk factors for malaria?

Answer 5

• 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

Question 6

What is the typical presentation of malaria?

Answer 6

P.falciparum usually incubates for 6 days and presents within 3 months of return from endemic area

Ask about stopovers

Non-specific symptoms:

• fever - can have a specific pattern if rupture of infected RBCs is synchronised.
• headache
• malaise
• myalgia
• diarrhoea
• cough

Severe disease:

• jaundice
• confusion
• seizures

Question 7

What investigations would you do for malaria?

Answer 7

1. Giemsa-stained thick and thin blood smear - parasite may be seen inside erythrocytes
   
   • Thick - shows that parasites are present
   • Thin - identifies species
2. 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

Question 8

How is malaria treated? (not on Sofia)

Answer 8

Artemisinin combination therapies (ACT) achieve rapid clearance of parasites by combined action at different stages of the parasite cycle:

1. Artemether-lumefantrine: 4 tablets at 0, 4, 8, 24, 36, 48, and 60h.
2. 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.