Malaria

A traveler returns from sub-Saharan Africa with cyclic fevers spiking every 48 hours — by the time you draw blood at the peak of the fever, the parasites are already destroying red blood cells at a rate that can kill within hours.

Malaria is caused by Plasmodium parasites transmitted through the bite of an infected female Anopheles mosquito, which feeds primarily between dusk and dawn. Five species infect humans; P. falciparum is the most lethal, causing over 90% of malaria deaths. P. vivax and P. ovale can form dormant liver stages (hypnozoites) that cause relapses months to years after initial infection. Global burden: over 240 million cases and 600,000+ deaths annually, primarily in sub-Saharan Africa, primarily children under 5. Incubation: typically 7–30 days. The hallmark presentation is cyclic paroxysms reflecting synchronous red blood cell lysis: cold stage (rigors, shaking chills, 2–3 hours), hot stage (high fever 40–41°C, headache, 3–4 hours), and sweating stage (profuse diaphoresis, temperature drops, 2–4 hours). Between paroxysms the patient may feel relatively well. Additional findings: splenomegaly (from RBC sequestration and immune response), hepatomegaly, anemia (from hemolysis), jaundice, and thrombocytopenia. Severe P. falciparum malaria: cerebral malaria (seizures, altered consciousness, coma), severe anemia (Hgb <7), ARDS, acute kidney injury, hypoglycemia (both from disease and quinine treatment), metabolic acidosis, and disseminated intravascular coagulation. Diagnosis: obtain STAT thick and thin blood smears immediately when malaria is suspected — do not delay for a fever spike. Thick smear detects parasites (highest sensitivity); thin smear identifies species and quantifies parasitemia. If initial smears are negative but suspicion remains high, repeat every 12–24 hours up to three sets. Rapid diagnostic tests (RDTs) detect parasite antigens and are useful in field settings. Treatment depends on species and resistance patterns: chloroquine for P. vivax, P. ovale, P. malariae, and chloroquine-sensitive P. falciparum. Artemisinin-based combination therapy (ACT) for chloroquine-resistant P. falciparum (most of sub-Saharan Africa and Southeast Asia). IV artesunate for severe malaria (medical emergency). Primaquine is added for P. vivax and P. ovale to eliminate hypnozoites and prevent relapse — but requires G6PD testing first (primaquine causes hemolytic anemia in G6PD-deficient patients). Chemoprophylaxis for travelers: atovaquone-proguanil, doxycycline, or mefloquine — selection depends on destination resistance patterns. Prevention: insecticide-treated bed nets (ITNs), DEET-containing repellent, indoor residual spraying, and avoiding outdoor exposure during peak mosquito feeding hours (dusk to dawn). Nursing: monitor for signs of severe malaria (neurologic changes, respiratory distress, severe anemia), check blood glucose frequently (hypoglycemia is common and dangerous), strict I&O for renal function, and assess for splenomegaly — avoid contact sports or abdominal trauma if markedly enlarged.

Key Distinctions

Cyclic fevers with travel to an endemic area = malaria until proven otherwise. Obtain STAT smears immediately when suspected — do not delay for a fever spike. If negative, repeat every 12–24 hours. Students confuse chloroquine (for sensitive species) with ACTs (for resistant P. falciparum) — treatment selection requires knowledge of geographic resistance. Primaquine for relapse prevention in P. vivax/ovale requires G6PD testing first — this is a high-yield pharmacology point. Anopheles mosquitoes bite at NIGHT (dusk to dawn), unlike Aedes mosquitoes (dengue/Zika) which bite during the DAY — prevention strategies differ accordingly.

Clinical Pearl

Cyclic fevers plus travel history — STAT smears now, don't wait for a spike. If negative and you still suspect it, repeat in 12 hours.