Ross River Virus Infection

Synonym: Epidemic polyarthritis

Ross River virus (RRV) is an RNA alphavirus. It is an arbovirus transmitted to man by mosquitoes, causing a polyarthritis. It is endemic in Australia where it is the commonest mosquito-borne disease affecting humans.¹ Infection can occur as a few sporadic cases, a small outbreak, or a major epidemic in certain climatic conditions.

• About 60% of cases arise in tropical and central Queensland (most commonly between January and May) but cases do occur throughout the rest of Australia and outbreaks have occurred in major Australian cities.
• Outbreaks have also occurred in Papua New Guinea, Indonesia and the Pacific Islands.
• Outbreaks are associated with high rainfall or high tides affecting salt marshes. This leads to an increase in mosquito numbers.²
• A similar mosquito-borne alphavirus, the Barmah Forest Virus (BFV), is the second most common mosquito-borne disease in Australia. The majority of notifications are in Queensland. It causes similar symptoms to RRV.³
• RRV does not occur in the UK but has potential to affect returning travellers.

Incidence

• On average, 4800 cases are notified each year in Australia.⁴
• There is likely to be significant underdiagnosis and under-reporting.
• BFV is less common but is becoming increasingly prevalent, possibly due to better recognition.³

• A variety of species of mosquito act as vectors for transmission of the virus from animal to human or human to human.
• There is a primary mosquito-mammal cycle involving kangaroos, wallabies, horses, possums, rodents and other vertebrates.
• A human-mosquito cycle may occur during epidemic outbreaks.⁵
• Incubation period is 3–21 days (average 9 days).⁶

Risk factors

• Camping increases risk eight-fold⁷
• Failure to take anti-mosquito precautions
• Adults (rarely affects young children)

Not all infected with RRV will become symptomatic.

Cardinal features

• Fever: mild pyrexia and minor constitutional symptoms of viral infection.
• Rash: present in two-thirds of cases. Can precede or follow other symptoms by up to 2 weeks and lasts for 7–10 days. May vary from a few spots on the hands and feet to whole-body involvement and can be indistinguishable from other viral exanthems such as rubella. Papules may be hypersensitive to touch and small vesicles can develop. Buccal and palatal lesions can occur.
• Symmetrical polyarthritis/migratory polyarthralgia: present in most except a few who just have rash alone. Can be markedly painful. Ankles, knees, fingers, elbow, feet and wrists are the most commonly affected joints, but others may be involved.

Other features

• Cervical lymphadenopathy can occur.
• Tendons (particularly the Achilles tendon) may become inflamed and sore.
• Paraesthesiae and tenderness of palms and soles occurs in a few cases.

• Dengue Fever
• Reactive arthritis (e.g. Reiter's syndrome, post-gastroenteritis)
• Ankylosing Spondylitis
• Acute Rheumatic Fever
• Lyme disease
• Rheumatoid arthritis, psoriatic arthritis
• Enteropathic arthropathies
• SLE
• Other causes of viral arthritis: parvovirus B19, viral hepatitis, rubella, HIV infection, mumps

• The diagnosis is confirmed by detection of specific antibodies to the RRV. A four-fold or higher rise in IgG antibody titre in acute and convalescent sera is usually seen.⁶ Presence of RRV specific IgM is diagnostic.
• The virus may be isolated from the blood of acutely ill patients in the early period of the disease.
• ELISA techniques have been developed for the rapid detection of antibodies.⁸

• There are no curative therapies.
• Treatment is directed at symptom relief and maintaining joint mobility.
• Paracetamol and NSAIDs are effective in reducing the severity of joint pain.

• Progressive resolution over 3-6 months is usual.^9,10
• A prolonged course can occur for up to 1 year with relapses and remissions.
• Infection can cause significant incapacity and absence from work for 2-3 months with economic implications.
• Recovery can occur in less than 1 month in mild cases.
• Complete recovery is eventually seen in all cases, with no long-term joint damage or complications.
• Infection probably means subsequent life-long immunity.

• Public health mosquito control measures (e.g. identification of mosquito breeding places and animal reservoirs, airport vector control)
• Climate analysis and epidemic prediction models⁴
• Use of mosquito repellents and coils
• Use of insect-knockdown sprays before retiring
• Anti-mosquito mesh on doors/windows in houses in affected areas
• Avoidance of water-storing objects around house
• Use of mosquito nets if camping
• Wear light-coloured loose-fitting clothing that covers all of arms and legs
• Avoid outdoor activity in mosquito-prone areas between dusk and dawn (when mosquitos usually bite)
• Research into potential vaccines is currently underway.¹¹

All alphaviruses are transmitted by mosquitoes. They tend to cause symptoms including fever, rash, myalgia and arthralgia. Some can cause encephalitis. Infection can also be asymptomatic. Alphaviruses are widely distributed and examples of other infections that they cause include:

• Chikungunya (East Africa, India, South East Asia, Philippines)
• O'nyong-nyong virus (East Africa)
• Mayaro virus (Central and South America)
• Sindbis virus (Asia, Africa, Europe, Australia, Philippines)
• Eastern Equine Encephalitis virus (Eastern states of North, Central and South America)
• Western Equine Encephalitis virus (North and South America)
• Venezuelan Equine Encephalitis virus (Southern USA, Central and South America)