Dermatology MCQ - Viral Infections - Lassa fever

A 30-year-old aid worker returns from Sierra Leone with a sudden onset of fever, sore throat, retrosternal pain, and generalized malaise. On examination, she has conjunctival injection, facial swelling, and petechiae on the palate and axillae. Laboratory tests reveal leukopenia, thrombocytopenia, and elevated transaminases. Which of the following is the most likely causative agent and its primary mode of transmission?

A) Plasmodium falciparum; mosquito bite
B) Lassa virus; exposure to aerosolized rodent excreta
C) Ebola virus; direct contact with bodily fluids
D) Rickettsia rickettsii; tick bite
E) Leptospira interrogans; contact with contaminated water

Correct Answer: B) Lassa virus; exposure to aerosolized rodent excreta

Explanation

This presentation is classic for Lassa fever, a viral hemorrhagic fever endemic to West Africa.

Key Clinical Features of Lassa Fever:

• Initial Symptoms: Fever, sore throat, retrosternal pain, malaise, and generalized weakness.

• Physical Signs:

  • Conjunctival injection (red eyes).

  • Facial swelling (edema).

  • Petechiae on the palate, axillae, and other mucous membranes (signs of capillary leak and thrombocytopenia).

• Severe Cases: Hemorrhage, shock, neurologic symptoms (deafness is a common sequela), and multi-organ failure.

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

Virologic Features:

• Causative Agent: Lassa virus, an arenavirus.

• Reservoir and Transmission:

  • Multimammate rat (Mastomys natalensis) is the natural reservoir.

  • Humans are infected through inhalation of aerosolized rodent urine or feces, or ingestion of contaminated food.

  • Human-to-human transmission occurs via direct contact with bodily fluids (secondary transmission).

Why Not the Other Options?

• (A) Plasmodium falciparum: Causes malaria (fever, chills, anemia), but not sore throat, petechiae, or facial swelling. Transmitted by mosquitoes.

• (C) Ebola virus: Causes hemorrhagic fever with similar features, but bleeding is more pronounced (e.g., hematemesis, melena). Transmitted via direct contact with bodily fluids; no rodent reservoir.

• (D) Rickettsia rickettsii: Causes Rocky Mountain spotted fever (fever, headache, rash [petechial later]), but not sore throat or facial swelling. Transmitted by ticks.

• (E) Leptospira interrogans: Causes leptospirosis (fever, conjunctival suffusion, jaundice), but not petechiae or pharyngitis. Transmitted via contact with contaminated water or soil.

Management:

• Supportive care: Fluid resuscitation, pain management, and treatment of complications.

• Antiviral: Ribavirin is effective if given early in the course of illness.

• Infection control: Strict isolation precautions to prevent human-to-human transmission.

Prognosis:
Overall mortality is ~1%, but can reach 15-20% in hospitalized cases. Deafness occurs in 25% of survivors.

Note: Lassa fever is a zoonotic disease with potential for nosocomial outbreaks. Early diagnosis and ribavirin treatment are critical.