Severe malaria — peripheral-smear interpretation, severity grading and artesunate rationale (clinical viva)

Interpretation

The examiner presents a peripheral blood smear showing multiple delicate ring forms within individual red cells, accolé (appliqué) rings at the cell margin, double-chromatin dots and a single crescent (banana)-shaped gametocyte, on a background of coarse black pigment. The clinical vignette: a non-immune adult returning from sub-Saharan Africa with a 5-day fever and progressive drowsiness. The examiner asks: "What do you see, what is the species, how severe is this patient, and how would you treat him?"

• Smear interpretation. Multiple rings per cell, appliqué rings, double chromatin and (pathognomonically) the crescent-shaped gametocyte identify Plasmodium falciparum. The banana gametocyte is never seen with the other four species. Schizonts are rare in peripheral blood in falciparum because they sequester in the microvasculature.^[1]
• Severity. Drowsiness + parasitaemia + impaired perfusion = potentially SEVERE. Apply the WHO 2014/2015 severity criteria (reproduced below). Any single criterion mandates IV artesunate + ICU.
• Differential. Dengue (retro-orbital pain, thrombocytopenia, NS1 positive), enteric fever (step-ladder fever, relative bradycardia, positive blood culture), leptospirosis (calf myalgia, conjunctival suffusion), scrub typhus (eschar), visceral leishmaniasis (chronic, massive splenomegaly, pancytopenia), bacterial sepsis. Co-infection is common — send blood cultures and a dengue NS1.

Key points

The examiner will probe each of these at viva depth; be ready to defend them:

1. Species morphology — falciparum: delicate rings, multiple per cell, appliqué, double chromatin, banana gametocyte, coarse black pigment; vivax: enlarged amoeboid trophozoite with Schüffner dots, 12-24 merozoite schizont; ovale: oval fimbriated cell; malariae: band trophozoite, rosette schizont; knowlesi: rings like falciparum, bands like malariae (PCR / specific RDT needed).^[1]
2. Diagnosis — THICK film for DETECTION (sensitivity down to ~50-100/μL); THIN film for SPECIES + PARASITAEMIA (parasitised RBCs per 1,000 RBCs, expressed as a percentage). Three negative smears at 12-24 h intervals are required to EXCLUDE malaria. RDT: HRP-2 (falciparum only, persists weeks) and pLDH (species-specific, clears in 1-2 weeks).
3. WHO severe malaria criteria (reproduced verbatim) — cerebral malaria (GCS under 11 / Blantyre 2 or less); prostration; respiratory distress / SpO2 under 92 per cent; shock (algid); abnormal bleeding/DIC; jaundice (bilirubin over 3 mg/dL); haemoglobinuria (blackwater); severe anaemia (Hb under 7 g/dL, under 5 in infants); hypoglycaemia (under 2.2 mmol/L); acidosis (bicarbonate under 15 / base deficit over 8 / lactate over 5 — the strongest mortality predictor); hyperparasitaemia (over 2 per cent, over 4 in pregnancy, over 10 in hyperendemic areas); AKI (creatinine over 3 mg/dL); ARDS; hyperpyrexia over 41 C.^[4]
4. Pathogenesis of severe falciparum — PfEMP-1 (encoded by the var gene family) on PRBCs binds endothelial ICAM-1, CD36, E-selectin, chondroitin sulphate A (placenta), thrombospondin, causing cytoadherence, sequestration and rosetting; cytokine storm (TNF-alpha, IFN-gamma) disrupts the blood-brain barrier; loss of endothelial protein C receptor links coagulation and inflammation to sequestration.^[4][5]
5. Treatment — IV artesunate. 2.4 mg/kg IV at 0, 12 and 24 h, then once daily until oral tolerated (3 mg/kg per dose in children under 20 kg). SEAQUAMAT (adults, 35 per cent relative mortality reduction vs quinine) and AQUAMAT (African children, 22.5 per cent reduction) established artesunate as the global standard.^[2][3]
6. Why artesunate over quinine? Faster parasite clearance, lower mortality, simpler dosing, no hypoglycaemia (quinine stimulates insulin release). Quinine is reserved for artesunate-unavailable settings.
7. Complications — cerebral malaria (15-20 per cent mortality, retinopathy is the most specific marker), severe anaemia (transfuse), ARDS (lung-protective ventilation, avoid fluid overload), AKI (haemofiltration), hypoglycaemia (IV dextrose, check hourly on quinine), DIC, blackwater fever (quinine-associated intravascular haemolysis), splenic rupture (vivax), post-artemisinin delayed haemolysis (PADH, up to 25 per cent of travellers — FBC at week 2 and 4).
8. Step-down — after at least 24 h of IV artesunate and falling parasitaemia, complete a 3-day oral course of ACT (artemether-lumefantrine 4 tablets BD × 3 days, with fatty food). For vivax/ovale add primaquine 0.25-0.5 mg/kg daily × 14 days AFTER G6PD assay; for falciparum a single low-dose primaquine (0.25 mg/kg) is gametocytocidal and reduces transmission.
9. Artemisinin resistance — slow parasite clearance linked to kelch-13 (K13) propeller mutations, first in western Cambodia and now across the Greater Mekong subregion; threatens the global ACT backbone; mitigation includes surveillance, longer courses and triple ACTs.^[7]
10. Prevention — chemoprophylaxis (atovaquone-proguanil, doxycycline, mefloquine), LLINs, IRS, and the RTS,S/AS01 (Mosquirix) vaccine recommended by WHO in 2021 for African children.

Likely follow-up questions

• "Why does the patient have hypoglycaemia?" — parasite glucose consumption PLUS quinine-driven hyperinsulinaemia (avoid quinine in pregnancy).
• "When can you exclude malaria with one negative smear?" — never; three smears at 12-24 h.
• "Why does pregnancy worsen malaria?" — placental sequestration (cytoadherence to chondroitin sulphate A); peripheral smear underestimates burden.
• "What is the difference between relapse, recrudescence and reinfection?" — relapse = hypnozoite (vivax/ovale, weeks-months); recrudescence = incomplete blood clearance (falciparum, days-weeks); reinfection = new inoculation.
• "Which antimalarials prolong the QTc?" — lumefantrine, piperaquine, quinine, chloroquine, mefloquine — avoid co-prescription.^[1]

References

1. Phillips MA, et al. Malaria. Nat Rev Dis Primers 2017.^[1]
2. Dondorp AM, et al. SEAQUAMAT. Lancet 2005.^[2]
3. Dondorp AM, et al. AQUAMAT. Lancet 2010.^[3]
4. Plewes K, et al. Coma and AKI in falciparum malaria. Curr Opin Infect Dis 2018.^[4]
5. Idro R, et al. Cerebral malaria. Lancet Neurol 2005.^[5]
6. Dondorp AM, et al. Artemisinin resistance in P. falciparum. N Engl J Med 2009.^[7]

References6ShowHide

1. [1]Phillips MA, et al. Malaria. Nat Rev Dis Primers, 2017.PMID 28770814
2. [2]Dondorp AM, et al. Artesunate versus quinine for treatment of severe falciparum malaria: a randomised trial (SEAQUAMAT). Lancet, 2005.PMID 16125588
3. [3]Dondorp AM, et al. Artesunate versus quinine in the treatment of severe falciparum malaria in African children (AQUAMAT). Lancet, 2010.PMID 21062666
4. [4]Plewes K, Turner GDH, Dondorp AM. Pathophysiology, clinical presentation, and treatment of coma and acute kidney injury complicating falciparum malaria. Curr Opin Infect Dis, 2018.PMID 29206655
5. [5]Idro R, Jenkins NE, Newton CRJC. Pathogenesis, clinical features, and neurological outcome of cerebral malaria. Lancet Neurol, 2005.PMID 16297841
6. [7]Dondorp AM, et al. Artemisinin resistance in Plasmodium falciparum malaria. N Engl J Med, 2009.PMID 19641202