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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Think malaria in any fever after travel to endemic areas, even if prophylaxis was taken
- Diagnosis: thick and thin blood smears repeated every 12-24 hours x3 if initially negative and suspicion remains
- P falciparum can cause severe disease: cerebral malaria, severe anemia, renal failure, ARDS, hypoglycemia, acidosis, shock
- Uncomplicated chloroquine-resistant falciparum: artemether-lumefantrine preferred if available, or atovaquone-proguanil
- Severe malaria: IV artesunate urgently, then complete oral therapy after parasitemia falls and patient can tolerate PO
- P vivax/ovale require primaquine or tafenoquine for hypnozoite eradication after G6PD testing
Overview
Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes. P falciparum is most likely to cause severe and fatal disease because infected erythrocytes sequester in microvasculature. P vivax and P ovale form dormant hepatic hypnozoites that can relapse unless eradicated. In the United States, malaria is usually imported, but prompt recognition is essential because falciparum malaria can progress quickly to coma, shock, and multi-organ failure.
Epidemiology
Most US cases occur in travelers, immigrants, or visitors from endemic regions, particularly sub-Saharan Africa, South Asia, Oceania, and parts of Latin America. Risk depends on itinerary, season, mosquito exposure, prophylaxis adherence, and local resistance. Severe disease is more common in nonimmune travelers, young children, pregnancy, older adults, and immunocompromised patients.
Clinical Features
Symptoms
Fever, chills, sweats, headache, malaise, myalgias after travel
Nausea, vomiting, diarrhea, abdominal pain can mimic gastroenteritis
Cyclic fevers may occur but are often absent early
Dark urine, jaundice, pallor from hemolysis
Confusion, seizures, coma, dyspnea, oliguria, bleeding, or shock suggests severe malaria
Relapsing fever weeks to months after travel suggests P vivax or P ovale
Signs
Fever with toxic appearance or altered mental status
Splenomegaly or hepatomegaly
Jaundice, pallor, petechiae, or dehydration
Tachypnea/Kussmaul respirations from acidosis in severe disease
Hypotension or reduced urine output suggests shock or renal failure
Investigations
First-line
Thick and thin blood smearsGold standard; thick smear is sensitive, thin smear identifies species and parasitemia percentage
Rapid diagnostic testUseful when microscopy delayed, but does not replace smears for speciation and parasitemia monitoring
CBC and CMPThrombocytopenia is common; anemia, bilirubin, creatinine, glucose, and transaminases assess severity
Second-line
Repeat smearsRepeat every 12-24 hours for 3 sets if initial smear negative and suspicion remains
Parasitemia quantificationHigh parasitemia supports severe disease and guides response to therapy
G6PD testingRequired before primaquine or tafenoquine for P vivax/ovale radical cure
Specialist
ICU-level evaluationSevere malaria, pregnancy, high parasitemia, altered mental status, acidosis, renal failure, ARDS, shock, or hypoglycemia
CDC malaria hotline consultationRecommended for severe disease, species uncertainty, pregnancy, or treatment access issues
Management
CDC Malaria Treatment Guidance1
Uncomplicated malaria
- Chloroquine-sensitive species/region: chloroquine or hydroxychloroquine
- Chloroquine-resistant P falciparum or unknown species from resistant area: artemether-lumefantrine preferred if available, or atovaquone-proguanil
- Alternatives include quinine plus doxycycline/tetracycline/clindamycin or mefloquine where appropriate
- Avoid presumptive treatment without diagnostic testing unless testing is unavailable and disease is strongly suspected
2
Severe malaria
- Treat immediately with IV artesunate
- Monitor glucose, lactate, renal function, hemoglobin, parasitemia, and respiratory status
- After IV artesunate and clinical improvement, complete a full oral regimen such as artemether-lumefantrine or atovaquone-proguanil
- Exchange transfusion is generally not routinely recommended in US guidance but specialist input is appropriate for extreme parasitemia
3
Relapsing malaria
- P vivax and P ovale need blood-stage therapy plus hypnozoite eradication with primaquine or tafenoquine
- Check G6PD before primaquine/tafenoquine to prevent severe hemolysis
- Avoid primaquine/tafenoquine in pregnancy; manage with specialist guidance
4
Prevention
- Chemoprophylaxis depends on destination: atovaquone-proguanil, doxycycline, mefloquine, chloroquine where sensitive, or tafenoquine in selected G6PD-normal adults
- Mosquito avoidance: DEET/picaridin, permethrin-treated clothing/bed nets, screened rooms, dusk-to-dawn protection
Complications
- Cerebral malaria: Seizures, coma, high mortality
- Severe hemolytic anemia: Pallor, jaundice, high bilirubin, hemoglobinuria
- AKI and acidosis: Severe falciparum disease marker
- ARDS: Can worsen after treatment begins
- Hypoglycemia: From severe infection and quinine/quinidine exposure
- Relapse: P vivax/ovale hypnozoites if no radical cure
USMLE Step 2 CK Exam Tips
- 1Any fever after travel to malaria-endemic area = malaria smear, even with prophylaxis
- 2Negative initial smear does not rule out malaria; repeat smears every 12-24 hours x3
- 3Severe malaria or cerebral symptoms = IV artesunate
- 4P falciparum is the species most associated with severe disease and cerebral malaria
- 5P vivax/ovale relapse from hypnozoites; give primaquine/tafenoquine only after G6PD testing
- 6Thrombocytopenia after travel is a classic malaria clue
- 7Atovaquone-proguanil and doxycycline are both prophylaxis options; chloroquine only for chloroquine-sensitive destinations
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