---

🦟 MALARIA - Complete Exam-Oriented Clinical Guide

---

1. DEFINITION

---

2. CAUSES (ETIOLOGY)

The Five Plasmodium Species

Exam tip: P. falciparum is responsible for almost all malaria deaths. P. knowlesi (Southeast Asia) looks like P. malariae on smear but behaves like falciparum.

Vector

• Only the female Anopheles mosquito transmits malaria
• Humans are the only natural reservoir

Other (Rare) Routes of Transmission

• Blood transfusion
• Needle sharing (IV drug users)
• Organ transplant
• Vertical (mother to fetus - congenital malaria)

Important Risk Factors

Exam pearl: Sickle cell trait, thalassemia, G6PD deficiency, and other red cell defects are most prevalent in malaria-endemic regions because heterozygous states confer protection from severe malaria - a classic example of balanced polymorphism.

---

3. TYPES / CLASSIFICATION

By Species (Most Clinically Important Classification)

• Fever every 48 hours (but often irregular in practice)
• Invades ALL ages of RBCs → high parasitemia
• Produces PfEMP1 → RBC sequestration in microvasculature
• Only species causing cerebral malaria, blackwater fever, multiorgan failure
• No hypnozoites → no true relapse (but recrudescence occurs)
• Drug resistance is a major problem

• Fever every 48 hours
• Only infect young/reticulocyte RBCs → lower parasitemia
• Contain hypnozoites (dormant liver stage) → TRUE RELAPSE after months/years
• Requires primaquine to eliminate liver stage
• P. ovale: found mainly in West Africa

• Fever every 72 hours ("quartan" = 4-day cycle)
• Infects old RBCs only
• Very chronic, low-grade
• Associated with nephrotic syndrome in children (immune complex deposition)
• No hypnozoites but can persist for decades

• 24-hour fever cycle (quotidian)
• Zoonotic from macaque monkeys in Southeast Asia (Borneo, Malaysia)
• Morphologically mimics P. malariae on blood smear
• Clinically can be severe and fatal

Fever Periodicity Summary

---

4. PATHOPHYSIOLOGY

Life Cycle Diagram (from Robbins Pathology)

Step-by-Step Pathophysiology Flowchart

Female Anopheles mosquito bites human
           ↓
SPOROZOITES injected into bloodstream
           ↓
Sporozoites travel to LIVER within minutes
(bind via Thrombospondin-related adhesive protein +
 Circumsporozoite protein → Heparan sulfate proteoglycan on hepatocytes)
           ↓
HEPATIC STAGE (clinically silent - 1-4 weeks incubation)
→ Sporozoites → differentiate into MEROZOITES inside hepatocytes
→ [P. vivax / P. ovale only: some form HYPNOZOITES = dormant stage → causes relapse later]
           ↓
Infected hepatocytes RUPTURE → release thousands of MEROZOITES into blood
           ↓
ERYTHROCYTIC STAGE begins (causes all clinical disease)
→ Merozoite surface lectin-like molecule binds GLYCOPHORIN (sialidated)
   on RBC surface → merozoite invaginates into RBC inside a "digestive vacuole"
           ↓
Inside RBC: Merozoite → RING TROPHOZOITE → TROPHOZOITE → SCHIZONT
           ↓
SCHIZONT expresses PfEMP1 (P. falciparum erythrocyte membrane protein 1)
→ PfEMP1 forms KNOBS on RBC surface
→ Knobs bind endothelial adhesion molecules: ICAM-1, VCAM-1, CD36
→ Infected RBCs SEQUESTER in capillary beds (brain, lung, kidney, placenta)
→ This causes CEREBRAL MALARIA, ARDS, renal failure
           ↓
Schizonts → differentiate into MEROZOITES → RBC LYSES (every 48 or 72 hrs)
→ Merozoites released → infect new RBCs (cycle repeats)
→ RBC lysis triggers fever (TNF-α, IL-1, IL-6 release)
→ Hemozoin (brown malarial pigment = hemoglobin breakdown product) released
           ↓
Some trophozoites → GAMETOCYTES → ingested by next mosquito → sexual cycle restarts

Why Each Key Problem Occurs

---

5. CLINICAL FEATURES

The Classic Malarial Paroxysm (Three Stages)

COLD STAGE (15-60 min)
→ Rigors (violent shaking chills), goose bumps, teeth chattering
→ Temperature RISING
           ↓
HOT STAGE (2-6 hours)
→ High fever (39-41°C / 102-106°F)
→ Flushing, headache, nausea, vomiting, body aches
→ No sweating yet
           ↓
SWEATING STAGE (2-4 hours)
→ Profuse sweating, temperature FALLS
→ Patient feels exhausted but better temporarily
→ Cycle repeats in 48 or 72 hours

Symptoms

Signs

Signs of Severe/Complicated Malaria (P. falciparum)

---

6. KEY SYMPTOMS THAT SUGGEST THE DIAGNOSIS

Hallmark Symptom

Cyclical paroxysms of chills → fever → profuse sweating in a patient from or traveling to an endemic area.

Classic Clinical Clues

Red Flag Findings (Admit Immediately - Severe Malaria)

• 🚨 Altered consciousness / coma (cerebral malaria)
• 🚨 Respiratory distress (ARDS)
• 🚨 Severe anemia (Hb < 7 g/dL)
• 🚨 Hyperparasitemia (>5% parasitized RBCs)
• 🚨 Hypoglycemia (<2.2 mmol/L)
• 🚨 Blackwater fever (hemoglobinuria)
• 🚨 Circulatory collapse / shock
• 🚨 Acute kidney injury
• 🚨 Abnormal bleeding / DIC
• 🚨 Repeated convulsions

Clinical pearl: In falciparum malaria, peripheral smear may show ONLY ring forms and gametocytes - all other stages are sequestered in deep microvasculature and invisible on blood film. This is why very low parasitemia on smear does NOT rule out severe falciparum malaria.

Protective genetics pearl (from Murray & Nadel): Nearly all genetic RBC defects - sickle cell anemia, thalassemia, pyruvate kinase deficiency, G6PD deficiency - are most prevalent in malaria-endemic regions. Heterozygous sickle cell trait is protective against severe falciparum malaria. This is textbook balanced polymorphism.

---

Quick Exam Summary Table

---

---

7. LABORATORY INVESTIGATIONS OF MALARIA

COMPLETE BLOOD COUNT (CBC)

Exam tip: Thrombocytopenia + normocytic anemia + fever in a traveler = malaria until proven otherwise.

---

BIOCHEMISTRY

---

DISEASE-SPECIFIC TESTS

---

IMAGING FINDINGS

---

Blood Smear Species Identification Quick Reference

---

8. DIFFERENTIAL DIAGNOSIS

Key exam principle: In any febrile traveler returning from sub-Saharan Africa or South/Southeast Asia, malaria is the presumptive diagnosis until ruled out by at least three negative blood smears taken 12-24 hours apart. Do not wait for smear results before treating if clinical suspicion is high - P. falciparum kills within days.

---

9. SHORT CLINICAL CASES

---

Case 1 - Classic Uncomplicated Malaria

• Travel to high-endemic West Africa (Ghana) + no prophylaxis = classic exposure history
• 48-hour cyclic fever with rigors and sweating = the three-stage malarial paroxysm
• Splenomegaly from RBC destruction and mononuclear phagocyte hyperplasia
• Thrombocytopenia (62,000) + normocytic anemia = hallmark CBC findings
• Elevated indirect bilirubin = hemolytic anemia
• Leukopenia (not leukocytosis) differentiates from bacterial sepsis
• Next step: Thick and thin blood smear (Giemsa) immediately + RDT; IV artesunate or oral ACT (artemether-lumefantrine) without delay

---

Case 2 - Severe/Cerebral Malaria (Red Flag Case)

• Age < 5-6 years in sub-Saharan Africa = highest-risk group for severe falciparum malaria
• Seizures + coma + fever = cerebral malaria (PfEMP1 knob-mediated sequestration of RBCs in cerebral microvasculature causing ischemia + inflammation)
• Banana-shaped (crescent) gametocytes on smear = pathognomonic for P. falciparum
• Hyperparasitemia >5% = WHO severity criterion
• Severe anemia (Hb 5.1) = immediate transfusion territory
• Hypoglycemia (1.8 mmol/L) = parasite glucose consumption + quinine-stimulated insulin; explain the seizures and coma
• Next step: IV artesunate IMMEDIATELY (first-line for severe falciparum per WHO 2023 guidelines); IV dextrose for hypoglycemia; blood transfusion; airway protection; do NOT delay treatment for confirmatory tests

Exam memory hook: "The 3 H's of severe falciparum malaria" = Hypoglycemia + Hyperparasitemia + Hemolysis (anemia) + one bonus - Headache progressing to coma (cerebral malaria).

---

---

10. TREATMENT OF MALARIA

A. NON-PHARMACOLOGICAL TREATMENT

Adjunctive treatments that are NOT recommended (per Harrison's): High-dose corticosteroids, heparin, dextran, urea, desferrioxamine, anti-TNF antibody - all have been studied and found ineffective or harmful in severe malaria. Do NOT use steroids in cerebral malaria.

---

B. PHARMACOLOGICAL TREATMENT

DRUG PRIORITY LEGEND

• 🥇 DOC / First-line
• 🥈 Alternative / Second-line
• 🚨 Emergency / Parenteral
• 🌿 Radical cure (anti-relapse)

---

PART 1: UNCOMPLICATED MALARIA

Chloroquine-Resistant / Unknown Resistance Areas (Most of the World)

---

Chloroquine-Sensitive Areas Only (Central America, Caribbean, parts of Middle East)

---

Radical Cure - Eliminating Hypnozoites (P. vivax and P. ovale ONLY)

---

PART 2: SEVERE / COMPLICATED MALARIA

Principle: IV artesunate is superior to quinine - reduces mortality by 35% in Asian adults and 22.5% in African children vs. quinine (Harrison's). It is now the WHO gold-standard for severe malaria.

After parenteral treatment: Switch to full course of oral ACT (artemether-lumefantrine or atovaquone-proguanil) as soon as patient can swallow. Add primaquine/tafenoquine if P. vivax or P. ovale (after G6PD check).

---

PART 3: CHEMOPROPHYLAXIS FOR TRAVELERS

---

11. CLINICAL PEARLS

Bedside Clues

• Periodic spiking fever + chills + sweating + thrombocytopenia in any patient with tropical travel history = malaria until proven otherwise. Order the smear before any other test.
• In early P. falciparum malaria, fever is often continuous and irregular - the classic 48-hour cycle develops later. Don't be misled into ruling out malaria because the fever isn't cyclic yet.
• A patient returning from West Africa with "flu-like illness" has malaria until 3 negative smears prove otherwise. The most common missed diagnosis in returning travelers is malaria misdiagnosed as influenza or viral fever.
• Splenomegaly + thrombocytopenia is the classic pairing. If spleen is palpable and platelets are low in a febrile patient - think malaria first.
• Splenic rupture warning: Any patient with malaria who develops sudden, severe left upper quadrant pain with hemodynamic instability has a ruptured spleen (most common with P. vivax). Surgical emergency.

High-Yield Exam Facts

• P. falciparum is the ONLY species with banana/crescent-shaped gametocytes → pathognomonic on blood smear.
• P. vivax and P. ovale have Schüffner's dots in enlarged RBCs.
• P. malariae has band-form (ribbon-form) trophozoites and infects only old RBCs → lowest parasitemia.
• Blackwater fever = massive hemolysis + hemoglobinuria + AKI - exclusive to P. falciparum (or quinine-induced hemolysis in G6PD-deficient patients).
• Artesunate IV reduced mortality by 35% vs. quinine in Asian trials and 22.5% in African children - this is a major viva/exam statistic.
• Do NOT use steroids in cerebral malaria - randomized trials showed higher mortality with glucocorticoids. This is a classic "do NOT do" viva question.
• Primaquine is contraindicated in pregnancy - G6PD status of fetus is unknown and risk of fetal hemolysis is unacceptable. Use chloroquine suppression weekly throughout pregnancy for P. vivax instead.
• G6PD testing is mandatory before primaquine or tafenoquine - these 8-aminoquinolines cause fatal hemolysis in G6PD-deficient patients.
• Chloroquine resistance in P. falciparum is mediated by mutation in PfCRT (chloroquine resistance transporter gene). This is the molecular mechanism.
• P. knowlesi has a 24-hour (quotidian) fever cycle - the fastest of all species.
• Malaria exerts evolutionary pressure: Sickle cell trait (HbAS), thalassemia, G6PD deficiency all provide partial protection → textbook example of balanced polymorphism.
• WHO severe malaria criteria to memorize: Cerebral malaria, severe anemia (Hb<7), ARDS, hyperparasitemia (>5%), hypoglycemia, AKI, DIC, shock, repeated seizures, hemoglobinuria.

High-Yield Viva Points

• Q: Why does malaria cause thrombocytopenia? A: Splenic sequestration of platelets + immune-mediated destruction (antibody-coated platelets).
• Q: Why can P. falciparum cause cerebral malaria but P. vivax cannot? A: Only P. falciparum expresses PfEMP1 (knobs) that bind ICAM-1/VCAM-1/CD36 on brain endothelium → RBC sequestration in cerebral microvasculature.
• Q: Why does the fever occur cyclically? A: Synchronized RBC rupture releases merozoites and pyrogens (TNF-α, IL-1, IL-6) every 48 or 72 hours.
• Q: Why is repeat smear needed? A: Parasitemia fluctuates; in early infection synchrony is incomplete; in P. falciparum, mature stages are sequestered. A single negative smear does NOT rule out malaria. Repeat 3 times over 24-48h.
• Q: What is the difference between relapse and recrudescence? A: Relapse = reactivation of dormant hypnozoites in liver (P. vivax/ovale only). Recrudescence = re-emergence from subtherapeutic blood-stage parasitemia (any species, including P. falciparum). P. falciparum does NOT relapse but can recrudesce.
• Q: Why is P. falciparum peripheral smear "ring-form only"? A: Schizonts and trophozoites are sequestered deep in microvasculature via PfEMP1 - they are not circulating in peripheral blood and therefore not seen on smear. A low-parasitemia smear in falciparum does NOT mean mild disease.

---

12. COMMON DIAGNOSTIC MISTAKES

---