Malarial Fever

Overview

Causative Organisms

Life Cycle & Pathogenesis of Fever

1. Sporozoites inoculated by mosquito → travel to liver within minutes
2. Intrahepatic schizogony: one sporozoite produces 10,000–30,000 merozoites
3. Erythrocytic cycle: merozoites invade RBCs → trophozoite → schizont → rupture, releasing new merozoites
4. Fever is triggered at schizont rupture: parasitized RBCs lyse synchronously, releasing hemozoin (malarial pigment), GPI anchors, and parasite debris → stimulates monocytes/macrophages → massive TNF-α and pro-inflammatory cytokine release → fever
5. Temperatures ≥40°C damage mature parasites, further synchronizing the cycle → produces the classic regular periodic fever pattern

The Malarial Paroxysm

1. Cold stage (15–60 min) — intense chills, shaking rigors, patient feels cold despite rising temperature
2. Hot stage (2–6 h) — high fever 39–41°C, headache, nausea, vomiting, dry skin
3. Wet stage (defervescence) — profuse sweating, temperature falls, patient feels exhausted but transiently better

"The hallmark of malaria is fever, often with a nonspecific influenza-like prodrome including headache and fatigue followed by a classic malarial paroxysm including chills, high fever, and then sweats."

Clinical Features

Uncomplicated Malaria

• Fever (may be continuous early on; cyclical later)
• Headache, myalgia, arthralgia
• Nausea, vomiting, diarrhea
• Splenomegaly, hepatomegaly, anemia
• Jaundice (hemolysis)

Severe / Complicated Malaria (P. falciparum)

Protective Host Genetics

• Sickle cell trait (HbA/S) — 6-fold reduction in severe falciparum malaria mortality; reduced PfEMP-1 surface expression
• HbC, HbE — partial protection
• G6PD deficiency — protective especially against P. vivax
• α-thalassemia — protects against severe disease after early frequent infections
• Duffy antigen negativity — near-complete protection against P. vivax (requires Duffy antigen for RBC invasion)

Diagnosis

• P. falciparum: multiple ring forms per RBC, banana-shaped gametocytes, no enlarged RBCs
• P. vivax/ovale: enlarged RBCs, Schüffner's dots, amoeboid trophozoites
• P. malariae: band-form trophozoites, "rosette" schizonts

Treatment

Uncomplicated Malaria

Severe Malaria

• IV artesunate — drug of choice for severe falciparum malaria worldwide
• IV quinine + doxycycline if artesunate unavailable
• Supportive: antipyretics, IV fluids, blood transfusion, mechanical ventilation as needed

Chemoprophylaxis

• Chloroquine (chloroquine-sensitive areas only)
• Atovaquone-proguanil (Malarone) — well tolerated, short pre/post travel course
• Doxycycline — daily; also covers other infections
• Mefloquine — weekly; neuropsychiatric side effects possible
• Primaquine — for P. vivax-endemic areas; check G6PD first

Epidemiology Note

IV Artesunate

Overview

"Artesunate is the drug of choice when available. Data from large studies in Southeast Asia showed a 35% lower mortality rate than with quinine, and very large studies in Africa showed a 22.5% reduction in mortality rate compared with quinine."

Mechanism of Action

1. Promiscuously alkylate a wide variety of parasite proteins
2. Oxidize and damage macromolecules within the parasite
3. May also form heme–artemisinin adducts that are directly toxic

• Active against asexual erythrocytic stages (rings through schizonts) — the stages responsible for clinical disease
• Also active against gametocytes → reduces onward transmission
• Each 48-hour erythrocytic cycle treated results in a ~4 log₁₀ (10,000-fold) reduction in parasite burden
• 3–4 treatment cycles (6–8 days) are required for complete parasite clearance

Pharmacokinetics (ADME)

Dosing Protocol — IV Artesunate for Severe Malaria

Indications

• Severe / complicated P. falciparum malaria (primary indication)
• P. knowlesi severe malaria
• Severe P. vivax malaria
• Any patient unable to take oral medications regardless of severity

Advantages Over Quinine

Adverse Effects

• Post-artesunate delayed haemolysis (PADH): A clinically important adverse effect — occurs 1–3 weeks after treatment; haemolysis of previously parasitized RBCs as they are re-released into circulation after splenic "pitting." Monitor Hb for 4 weeks post-treatment in non-immune patients (travelers).
• Transient neutropenia
• Mild transaminase elevation
• Neurotoxicity: Reported in animal studies at high doses; not established in clinical use at therapeutic doses.
• First-trimester pregnancy: Use with caution — limited data, but WHO recommends artesunate even in the first trimester for severe malaria (benefit outweighs risk).

Resistance

Drug Stage Activity Summary

Primaquine

Overview

"Primaquine, in contrast to other antimalarials, acts on exerythrocytic tissue stages of Plasmodium spp. in the liver to prevent and cure relapsing malaria. Patients should be screened for G6PD deficiency prior to therapy."

Chemical Class

• 8-aminoquinoline (distinguished from 4-aminoquinolines like chloroquine)
• Structurally related to tafenoquine (its long-acting successor)

Mechanism of Action

1. Oxidative disruption of the electron transport chain in the parasite's mitochondria
2. Metabolites oxidize glutathione (GSH → GSSG), depleting the parasite's and, critically, the RBC's antioxidant defence
3. This same oxidative mechanism underlies both schizonticidal activity and the haemolytic toxicity in G6PD-deficient patients

Spectrum of Activity — Stage Specificity

Pharmacokinetics

Clinical Uses

1. Radical Cure of P. vivax and P. ovale Malaria

• Chloroquine first → eradicates erythrocytic forms (terminates the acute attack)
• Then primaquine 15 mg base/day × 14 days → eradicates liver hypnozoites and prevents relapse

Primaquine appears most effective when started before completion of chloroquine dosing — G6PD status must be checked first.

2. Terminal Prophylaxis (Post-exposure)

3. Primary Chemoprophylaxis

• Primaquine 30 mg base (0.5 mg/kg) once daily — CDC-listed alternative prophylactic regimen
• Effective against both P. falciparum and P. vivax
• Targets primary liver stages of P. falciparum (no hypnozoites in P. falciparum)
• Must be taken daily; started 1–2 days before travel, continued 7 days after return

4. Gametocidal Action — Transmission Blocking

• Renders P. falciparum gametocytes non-infective to mosquitoes
• A single low dose (0.25 mg base/kg) added to falciparum treatment reduces onward transmission
• WHO recommends this in low-transmission settings; may be safe even without G6PD testing at low doses

5. Pneumocystis jirovecii Pneumonia (PCP)

• Clindamycin + primaquine is an alternative regimen for mild-to-moderate PCP
• Better tolerated than high-dose TMP-SMX or pentamidine; less data for severe disease

The Critical Adverse Effect: G6PD-Related Haemolysis

• RBCs rely on the hexose monophosphate shunt (G6P → Ribose-5-P) to generate NADPH
• NADPH maintains glutathione (GSH) in its reduced, protective form
• Primaquine metabolites oxidize GSH → GSSG, generating reactive oxygen species
• In G6PD-deficient patients, NADPH cannot be regenerated → RBCs are overwhelmed by oxidative stress → Heinz body formation → intravascular haemolysis

• African variant (A−): Milder haemolysis (only older RBCs affected; reticulocytes relatively protected)
• Mediterranean variant: Severe haemolysis; affects all RBC ages

• Mild deficiency: Weekly primaquine 45 mg × 8 weeks (alternative under supervision)
• Severe deficiency: Primaquine contraindicated → consider tafenoquine is also contraindicated → no radical cure option; accept risk of relapse with chloroquine as suppressive therapy

Other Adverse Effects

Contraindications

Primaquine vs. Tafenoquine

Summary: Why Primaquine Is Irreplaceable

1. Eradicates hypnozoites → prevents relapse of P. vivax / P. ovale
2. Kills gametocytes of all Plasmodium species → reduces community transmission
3. Covers primary liver stages → useful for prophylaxis