Dermatology MCQ - Viral Infections - Barmah Forest virus

A 38-year-old woman presents with acute onset of fever, polyarthralgia, and a generalized maculopapular rash after a hiking trip in coastal New South Wales, Australia. She reports significant fatigue and swelling in her wrists and ankles. Laboratory studies show mild leukopenia and elevated C-reactive protein (CRP). Which of the following is the most likely causative agent and its primary reservoir host?

A) Ross River virus; marsupials
B) Barmah Forest virus; marsupials
C) Dengue virus; humans
D) Chikungunya virus; primates
E) Sindbis virus; birds

Correct Answer: B) Barmah Forest virus; marsupials

Explanation

This presentation is characteristic of Barmah Forest virus (BFV) infection, an arboviral disease endemic to Australia that closely mimics Ross River virus (RRV) disease.

Key Clinical Features of Barmah Forest Virus Infection:

• Symptoms:

  • Fever (often mild).

  • Polyarthralgia: Symmetric joint pain and swelling, commonly affecting wrists, knees, ankles, and small joints of the hands.

  • Rash: Generalized maculopapular or vesicular rash that may be pruritic; often more prominent than in RRV infection.

  • Fatigue: Can be profound and prolonged.

• Laboratory Findings: Mild leukopenia, elevated CRP or ESR (indicating inflammation).

• Epidemiology: Found primarily in Australia, especially in coastal regions (e.g., New South Wales, Queensland). Outbreaks occur after heavy rainfall and flooding.

Virologic and Transmission Features:

• Causative Agent: Barmah Forest virus (an alphavirus in the Togaviridae family).

• Vector: Transmitted by mosquitoes, including Culex annulirostris and Aedes normanensis.

• Reservoir Host: Marsupials (e.g., kangaroos, wallabies) serve as the primary amplifying hosts, similar to RRV.

Why Not the Other Options?

• (A) Ross River virus: Causes nearly identical symptoms (fever, polyarthralgia, rash) and shares the same reservoir (marsupials). However, BFV is distinguished by a higher frequency of rash and less severe arthralgia on average. Geographic and seasonal patterns overlap, but BFV is less common than RRV.

• (C) Dengue virus: Causes fever, rash, and arthralgia but is not endemic in Australia (except limited areas in Far North Queensland). Humans are the primary reservoir.

• (D) Chikungunya virus: Causes severe polyarthralgia and rash but is not endemic in Australia. Primates are the reservoir.

• (E) Sindbis virus: Causes fever, rash, and arthralgia (e.g., Ockelbo disease) but is not found in Australia. Birds are the reservoir.

Management:

• Supportive care: NSAIDs for pain and inflammation, rest, and hydration.

• No specific antiviral treatment or vaccine is available.

• Prevention: Mosquito avoidance (repellents, protective clothing).

Prognosis:
Symptoms typically resolve within 1-2 months, but some patients may experience persistent fatigue and arthralgia.

Note: Barmah Forest virus and Ross River virus are the two most common causes of arboviral polyarthritis in Australia. BFV is often underdiagnosed due to its similarity to RRV. Serologic testing (IgM ELISA) is required to distinguish between them. Always consider BFV in patients with a rash-predominant presentation following exposure in endemic Australian regions.