Dermatology MCQ - Viral Infections - Yellow Fever

A 28-year-old unvaccinated traveler returns from a jungle expedition in Brazil with a sudden onset of high fever, headache, and myalgia. After a brief period of remission, he develops jaundice, vomiting, and epistaxis. Laboratory studies show leukopenia, elevated transaminases (AST > ALT), hyperbilirubinemia, and proteinuria. Which of the following is the most likely diagnosis and the vector responsible for transmission?

A) Dengue fever; Aedes aegypti mosquito
B) Yellow fever; Aedes aegypti or Haemagogus mosquito
C) Leptospirosis; contact with contaminated water
D) Viral hepatitis A; fecal-oral transmission
E) Malaria; Anopheles mosquito

Correct Answer: B) Yellow fever; Aedes aegypti or Haemagogus mosquito

Explanation

This presentation is classic for yellow fever, a viral hemorrhagic fever with a characteristic biphasic course.

Key Clinical Features of Yellow Fever:

• Initial Phase (Period of Infection): Sudden onset of high fever, headache, myalgia, nausea, and relative bradycardia (Faget's sign). Lasts 3-4 days.

• Period of Remission: Symptoms abate for ~24 hours.

• Toxic Phase (Period of Intoxication): ~15-25% of patients progress to this severe phase, featuring:

  • Jaundice (due to liver involvement).

  • Hemorrhagic manifestations (epistaxis, gum bleeding, melena).

  • Renal dysfunction (proteinuria, oliguria).

  • Vomiting (often black due to gastric bleeding — "coffee ground emesis").

• Laboratory Findings: Leukopenia, elevated transaminases (AST > ALT), hyperbilirubinemia, coagulopathy, and proteinuria.

Virologic and Epidemiologic Features:

• Causative Agent: Yellow fever virus (a flavivirus).

• Transmission:

  • Urban cycle: Transmitted by the Aedes aegypti mosquito.

  • Jungle (sylvatic) cycle: Transmitted by Haemagogus and Sabethes mosquitoes (as in this case, from a jungle expedition).

• Reservoir: Primates (monkeys) in the jungle cycle.

Why Not the Other Options?

• (A) Dengue fever: Causes fever, headache, myalgia, and rash, but jaundice and significant hemorrhage are rare except in severe dengue. Lab findings show thrombocytopenia but not typically AST > ALT or hyperbilirubinemia.

• (C) Leptospirosis: Causes fever, jaundice, and hemorrhage (Weil's disease) but is acquired through contact with water contaminated by animal urine. It does not have a biphasic course or mosquito vector.

• (D) Viral hepatitis A: Causes jaundice and elevated transaminases but is transmitted via the fecal-oral route. It does not cause hemorrhage, leukopenia, or a biphasic illness.

• (E) Malaria: Causes fever, jaundice, and can have a relapsing course, but jaundice is hemolytic (not hepatic), and lab findings show hemolytic anemia (not AST > ALT). Transmitted by Anopheles mosquitoes.

Management:

• Supportive care: No specific antiviral treatment. Focus on fluid management, transfusion for hemorrhage, and renal support.

• Prevention: Live attenuated vaccine (17D) is highly effective and provides lifelong immunity. Required for travel to endemic areas.

Prognosis:
Case fatality rate in the toxic phase is 20-50%. Survivors have lifelong immunity.

Note: Yellow fever is preventable by vaccination. The "yellow" refers to jaundice. Always consider vaccination status in travelers with fever and jaundice.