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Malaria: From Basics to Clinics

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1. WHAT IS MALARIA? (Simple Definition)

More than 200 million cases occur worldwide annually, causing over 600,000 deaths - most in sub-Saharan African children under 5 years old.

• Robbins & Kumar Basic Pathology

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2. CAUSES (Etiology)

The Parasites - 5 Species Infect Humans

The Vector

• Exclusively the female Anopheles mosquito (males don't bite)
• Bites primarily at dusk and dawn
• Humans are the only natural reservoir

Other (Rare) Routes of Transmission

• Blood transfusions
• Needle sharing (IV drug use)
• Organ transplantation
• Mother-to-fetus (congenital malaria)

Where Is It Found?

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3. PATHOPHYSIOLOGY (How It Causes Disease)

The Life Cycle - Step by Step

Step 1 - Entry (Mosquito Bite)

Step 2 - Liver Stage (Hepatic Phase, 1-4 weeks)

• Sporozoites use two surface proteins (thrombospondin-related adhesive protein and circumsporozoite protein) to bind to proteoglycans on hepatocytes
• Inside the liver, they multiply and transform into merozoites
• After 1-4 weeks, infected hepatocytes rupture, releasing thousands of merozoites into the blood
• Key point for P. vivax and P. ovale: Some parasites can remain dormant in the liver as hypnozoites - these cause relapses months or years later

Step 3 - Blood Stage (Erythrocytic Phase) - Where Symptoms Happen

1. A lectin-like molecule on the merozoite surface binds to glycophorin (a red cell protein), allowing invasion
2. Inside the RBC, the parasite forms a ring trophozoite inside a "digestive vacuole"
3. Trophozoites differentiate into schizonts, which express PfEMP1 (Plasmodium falciparum Erythrocyte Membrane Protein 1) - this protein forms "knobs" on the RBC surface
4. PfEMP1 binds to adhesion molecules on blood vessel walls (ICAM-1, VCAM-1, CD36) → parasitized RBCs stick to capillary walls (sequestration) - this is the key mechanism of severe disease
5. After several days, schizonts rupture → release more merozoites → infect more RBCs → this synchronized rupture causes the cyclical fever
6. Some trophozoites become gametocytes (sexual forms) - if another mosquito bites this person, the cycle restarts in the mosquito

Why Does This Cause Damage?

"The destruction of red cells leads to hemolytic anemia... A characteristic brown malarial pigment derived from hemoglobin called hematin is released from the ruptured red cells and produces discoloration of the spleen, liver, lymph nodes, and bone marrow." - Robbins & Kumar Basic Pathology

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4. SYMPTOMS (Clinical Presentation)

The Classic Malaria Attack - "The Fever Paroxysm"

• Every 24 hours (quotidian) → P. knowlesi
• Every 48 hours (tertian) → P. falciparum, P. vivax, P. ovale
• Every 72 hours (quartan) → P. malariae

Other Common Symptoms

• Headache (very common, often severe)
• Myalgia and arthralgia (muscle and joint pains)
• Nausea, vomiting, anorexia
• Abdominal pain (can mimic gastroenteritis)
• Diarrhea (up to 30% of cases - often misdiagnosed as gastroenteritis)
• Fatigue and malaise
• Pallor (from anemia)
• Jaundice (from RBC hemolysis)
• Splenomegaly (especially in chronic or recurrent infection)
• Hepatomegaly (less common)

"Although it is classically associated with cyclical fevers, malaria presents various symptoms, including headache and diarrhea. Fever is common but not universal at initial presentation." - Rosen's Emergency Medicine

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5. SIGNS OF SEVERE / COMPLICATED MALARIA (P. falciparum)

Specific Severe Complications

• Parasitized RBCs with PfEMP1 knobs adhere to cerebral capillaries → sludging, ischemia, petechial hemorrhages, cerebral edema
• Features: fever + altered mental status + coma + seizures
• Rapidly fatal if untreated - mainly kills children

• Massive intravascular hemolysis → hemoglobinemia + hemoglobinuria + jaundice + renal failure
• Urine turns dark brown or black (hence the name)
• Associated with P. falciparum, especially with quinine treatment

• Hemoglobin can fall to critically low levels from:
  • Direct lysis of parasitized RBCs
  • Immune destruction of non-parasitized RBCs (antibody-mediated)
  • Inhibited erythropoietin response
  • Splenic sequestration

• Cytokine-driven capillary leak in the lungs
• High mortality, can develop even after treatment begins

• Especially dangerous in children and pregnant women
• Two mechanisms: parasite consumes glucose directly; quinine stimulates insulin release

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6. BLOOD SMEAR APPEARANCE (Microscopic Diagnosis)

• Multiple ring forms per RBC (other species only have one)
• Rings at the periphery of the RBC ("appliqué" or "accolé" forms)
• Banana/crescent-shaped gametocytes - pathognomonic for P. falciparum
• No enlargement of infected RBC (P. vivax enlarges the RBC)
• No Schüffner's dots (P. vivax and ovale have these)

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7. DIFFERENTIAL DIAGNOSIS

Common Conditions to Rule Out First

Conditions to Distinguish from Severe Malaria

"Cerebral malaria may manifest with confusion and mental status changes and should be differentiated from meningitis and encephalitis." - Rosen's Emergency Medicine

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8. SYMPTOMS THAT CONFIRM THE DIAGNOSIS (Pathognomonic / Highly Specific Features)

Clinical Features Highly Suggestive

1. Periodic fever with rigors - The classic synchronized cycle (every 48 or 72 hours) is the most characteristic symptom. When the fever paroxysm is clearly cyclical with cold-hot-sweating stages, malaria is the top differential.
2. Banana/crescent-shaped gametocytes on blood smear - Pathognomonic for P. falciparum. Nothing else looks like this.
3. Travel to endemic region + fever - Sensitivity of fever and/or headache > 95% in low-endemicity areas.
4. Splenomegaly in a febrile traveler - Not diagnostic alone, but adds strong specificity.
5. Hemoglobinuria (dark urine) + fever - Blackwater fever; very specific for severe falciparum malaria.

Definitive Diagnostic Criteria (from Harrison's)

• Thick and thin blood smears (Giemsa stain at pH 7.2) - GOLD STANDARD
  • Thick smear: more sensitive (concentrates parasites)
  • Thin smear: identifies species and counts parasitemia
  • If smear is negative by an experienced microscopist → patient does not have malaria
• Rapid Diagnostic Tests (RDTs) - Antigen-based dipstick tests; used when reliable microscopy is unavailable
• PCR - Most sensitive; used for low parasitemia or species confirmation

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9. TREATMENT (Overview)

Uncomplicated Malaria

Severe / Complicated Malaria

• IV Artesunate - First-line worldwide; superior to quinine (2.4 mg/kg IV every 12 hrs on day 1, then daily)
• IV Quinine - Alternative if artesunate unavailable
• Supportive care: IV fluids, blood transfusion, anti-seizure medication, ventilation as needed

Chemoprophylaxis for Travelers

• Atovaquone-proguanil (Malarone) - Daily; start 1-2 days before, continue 7 days after
• Mefloquine - Weekly; start 2-3 weeks before
• Doxycycline - Daily; start 1-2 days before
• Chloroquine - Weekly; only in chloroquine-sensitive areas

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10. QUICK SUMMARY TABLE

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