Dermatology MCQ - Viral Infections - Sindbis virus infection

A 45-year-old woman presents with fever, arthralgia, and a rash on her trunk and extremities that began after a hiking trip in Northern Europe. The rash consists of erythematous macules and papules, some with vesicles. She reports swollen and painful wrists and ankles. Which of the following is the most likely causative agent and its vector?

A) Borrelia burgdorferi; Ixodes tick
B) Sindbis virus; Culex mosquito
C) Rickettsia rickettsii; Dermacentor tick
D)) Dengue virus; Aedes mosquito
*E)) Leptospira interrogans; contact with contaminated water

Correct Answer: B) Sindbis virus; Culex mosquito

Explanation

This presentation is classic for Sindbis virus infection, also known as Ockelbo disease in Sweden, Pogosta disease in Finland, and Karelian fever in Russia.

Key Clinical Features of Sindbis Virus Infection:

• Triad of Symptoms:

  1. Fever (usually mild).

  2. Rash: Often begins on the trunk and spreads to extremities. It starts as erythematous macules and papules that may evolve into vesicles or become hemorrhagic. The rash can be pruritic.

  3. Arthralgia/Arthritis: Particularly affecting the wrists, ankles, and knees. The joint pain can be severe and persist for months.

• Epidemiology: Most common in Northern Europe (especially Scandinavia), Northern Asia, and Africa.

• Incubation: Typically 3-7 days after mosquito bite.

Virologic and Transmission Features:

• Causative Agent: Sindbis virus, an alphavirus in the Togaviridae family.

• Vector: Primarily transmitted by Culex mosquitoes (e.g., Culex pipiens, Cx. torrentium).

• Reservoir: Birds (enzootic cycle between birds and mosquitoes). Humans are incidental hosts.

Why Not the Other Options?

• (A) Borrelia burgdorferi: Causes Lyme disease, which can present with fever, arthralgia, and rash (erythema migrans - a bull's-eye rash), but not vesicles. Vector is Ixodes tick.

• (C) Rickettsia rickettsii: Causes Rocky Mountain spotted fever, which presents with fever, headache, and a petechial rash (not typically vesicular). Vector is Dermacentor tick.

• (D) Dengue virus: Causes dengue fever with fever, rash (maculopapular), and arthralgia, but the rash is rarely vesicular. Vector is Aedes mosquito. Dengue is not endemic in Northern Europe.

• (E) Leptospira interrogans: Causes leptospirosis, which presents with fever, conjunctival injection, and myalgia, but not a vesicular rash. Transmission is via contact with contaminated water or soil.

Management:

• Supportive care: NSAIDs for arthralgia, antihistamines for pruritus.

• No specific antiviral treatment is available.

• Most infections are self-limiting, though arthralgia may persist for months.

Prognosis:
Excellent; full recovery is typical, though some patients may have prolonged arthritis.

Note: Sindbis virus is a classic example of an arthropod-borne virus (arbovirus) causing a benign febrile illness with rash and arthritis. Always consider travel history and local vector activity.