Dermatology MCQ - Viral Infections - Ross River virus

A 42-year-old man presents with fever, polyarthralgia, and a rash after a camping trip in rural Australia. The arthralgia is particularly severe in his wrists, knees, and ankles, and he reports a generalized maculopapular rash that started on his trunk. Laboratory studies show leukopenia and elevated erythrocyte sedimentation rate (ESR). Which of the following is the most likely causative agent and its primary vector?

A) Ross River virus; Culex and Aedes mosquitoes
B) Dengue virus; Aedes aegypti mosquito
C) Barmah Forest virus; Aedes and Culex mosquitoes
D) Murray Valley encephalitis virus; Culex mosquito
E) Sindbis virus; Culex mosquito

Correct Answer: A) Ross River virus; Culex and Aedes mosquitoes

Explanation

This presentation is classic for Ross River virus (RRV) disease, the most common arboviral disease in Australia, also known as epidemic polyarthritis.

Key Clinical Features of Ross River Virus Disease:

• Triad of Symptoms:

  1. Polyarthralgia: Often severe and debilitating, affecting multiple joints (wrists, knees, ankles, small joints of hands).

  2. Rash: Maculopapular or vesicular rash, typically starting on the trunk and limbs, often resolving within 1-2 weeks.

  3. Fever: Low-grade or absent in some cases.

• Other Symptoms: Myalgia, fatigue, lymphadenopathy.

• Laboratory Findings: Leukopenia, elevated ESR/CRP (indicating inflammation).

• Epidemiology: Common in Australia, Papua New Guinea, and the Pacific Islands. Outbreaks often occur after heavy rainfall and flooding.

Virologic and Transmission Features:

• Causative Agent: Ross River virus (an alphavirus in the Togaviridae family).

• Vector: Transmitted by various mosquitoes, including Culex annulirostris and Aedes vigilax (saltwater mosquito) and Aedes camptorhynchus.

• Reservoir: Marsupials (e.g., kangaroos, wallabies) are the primary amplifying hosts.

Why Not the Other Options?

• (B) Dengue virus: Causes fever, rash, and arthralgia but is less associated with severe polyarthritis and is not endemic in Australia (except in Far North Queensland). Transmitted by Aedes aegypti.

• (C) Barmah Forest virus: Causes a similar illness (fever, polyarthralgia, rash) but is less common than RRV. It is also transmitted by Culex and Aedes mosquitoes, but RRV is more prevalent.

• (D) Murray Valley encephalitis virus: Causes encephalitis, not polyarthritis or prominent rash. Transmitted by Culex mosquitoes.

• (E) Sindbis virus: Causes fever, rash, and arthralgia (e.g., Ockelbo disease in Europe) but is not endemic in Australia. Transmitted by Culex mosquitoes.

Management:

• Supportive care: NSAIDs for pain and inflammation. Rest during acute phase.

• No specific antiviral treatment or vaccine is available.

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

Prognosis:
Most patients recover within 3-6 months, but some may experience chronic arthralgia and fatigue for years.

Note: Ross River virus is a major cause of arboviral arthritis in Australia. The combination of polyarthralgia, rash, and exposure in endemic areas is highly suggestive. Always consider RRV in travelers returning from Australia with these symptoms.