Malaria

Detailed Overview

Five species of Plasmodium infect humans: P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. P. falciparum is the most deadly, causing severe microvascular pathology and cerebral malaria, predominantly in sub-Saharan Africa. P. vivax and P. ovale can establish dormant liver stages (hypnozoites) causing relapses months or years later. The classic paroxysm of chills, fever, and sweating corresponds to the synchronized rupture of infected red blood cells. Prompt diagnosis via microscopy or rapid diagnostic tests (RDTs) and artemisinin-based combination therapies (ACTs) are critical for survival.

Epidemiology & Demographics

Approximately 240 million cases and 600,000 deaths annually worldwide, overwhelmingly in sub-Saharan Africa. Children under 5 years old account for 80% of deaths. Rare in the US (travel-associated).

Etiological Mechanism

Infection by Plasmodium spp. following injection of sporozoites by an infected female Anopheles mosquito.

Primary Causes

Bite from an infected Anopheles mosquito. Less commonly: blood transfusion, organ transplant, or congenital transmission.

• Travel to Endemic Area: Without adequate chemoprophylaxis or mosquito bite prevention.
• Age: Children <5 years lack acquired partial immunity, increasing risk of severe disease.
• Pregnancy: Pregnant women are at high risk for severe malaria and placental infection leading to low birth weight.

Sporozoites enter the blood and travel to the liver, infecting hepatocytes and multiplying asexually into thousands of merozoites (exoerythrocytic phase). Merozoites burst from the liver and infect red blood cells (RBCs), maturing from ring forms to trophozoites to schizonts. The synchronized rupture of RBCs releases toxins, triggering massive TNF-alpha and cytokine release (causing fever/chills). In P. falciparum, infected RBCs express PfEMP1, causing them to cytoadhere to capillary endothelium and rosette with uninfected RBCs. This causes microvascular obstruction, tissue hypoxia, and severe organ dysfunction (cerebral malaria, acute kidney injury, pulmonary edema).

Characteristic Clinical Presentation

• Febrile Paroxysm: Cyclical sudden onset of severe chills/rigors followed by high fever (>40C) and profuse sweating.
• Fatigue and Malaise: Profound weakness due to progressive hemolytic anemia.
• Headache & Myalgia: Severe generalized body aches commonly preceding the fever.
• Gastrointestinal: Nausea, vomiting, and diarrhea, particularly in children.

Physical Examination Signs

• Pallor (due to anemia).
• Hepatosplenomegaly (enlargement of liver and spleen due to clearing of infected RBCs).
• Jaundice (due to hemolysis).
• Altered mental status or coma (indicative of Cerebral Malaria).

• Cerebral Malaria: Microvascular occlusion in the brain leading to seizures, coma, and high mortality.
• Severe Anemia: Massive destruction of RBCs requiring transfusion.
• Blackwater Fever: Massive intravascular hemolysis leading to hemoglobinuria and dark urine.
• Acute Kidney Injury: Due to ATN from hemoglobinuria and microvascular obstruction.

Diagnostic Criteria & Guidelines

Visualization of parasites on thick and thin Giemsa-stained blood smears. Thick smear for detection, thin smear for species identification and calculating percent parasitemia.

Differential Diagnosis

• Dengue Fever
• Typhoid Fever
• Meningitis
• Leptospirosis

Laboratory Tests & Biomarkers

• Thick and Thin Blood Smears: Ring forms, trophozoites, or banana-shaped gametocytes (P. falciparum).
• Rapid Diagnostic Test (RDT): Positive for HRP2 (P. falciparum specific) or Plasmodium aldolase/pLDH.
• CBC: Normocytic normochromic anemia, thrombocytopenia (<100,000/uL).

Imaging Modalities & Findings

• Not typically indicated:

• Uncomplicated Malaria
  Fever and parasitemia without signs of severe end-organ damage.
• Severe Malaria
  P. falciparum parasitemia >5%, severe anemia, ARDS, AKI, or cerebral involvement.

Second-Line & Adjunctive Therapy

Uncomplicated alternative: Atovaquone-proguanil (Malarone) 250/100mg, 4 tablets daily for 3 days.

Surgical & Procedural Management

None. Splenectomy only in the rare case of spontaneous splenic rupture.

Recommended Lifestyle Changes

• Rest and adequate hydration.
• Sleep under insecticide-treated bed nets to prevent further mosquito transmission.

Patient Counseling & Advice

Advise patients completing treatment for P. vivax/ovale of the importance of the 14-day primaquine course to prevent relapse. Counsel on future travel prophylaxis.

Follow-Up & Monitoring Schedule

Repeat blood smears daily until parasitemia clears. Follow CBC for 1 month as delayed hemolysis can occur with certain therapies.

Preventive Strategies

Chemoprophylaxis for travelers (e.g., Atovaquone-proguanil, Doxycycline, or Mefloquine). Vector control via indoor residual spraying. RTS,S/AS01 (Mosquirix) vaccine for children in endemic regions.

Excellent for uncomplicated malaria treated promptly. Severe P. falciparum malaria has a 15-20% mortality rate even with optimal intensive care.