Ross River Virus

Definition

Ross River Virus (RRV) is Australia's most common and widespread mosquito-borne pathogen. Also known as RRV disease, it can cause debilitating polyarthritis, rash, fever, and constitutional symptoms.

Description

Originally known as epidemic polyarthritis, RRV is a member of the Togaviridae family of arboviruses. RRV is transmitted in an animal host-vector-human cycle, where the vector is the mosquito. Serological investigations have indicated that native macropods are the main vertebrate hosts of RRV, although other animals can become infected as well. The RRV lives in the blood stream of an infected animal. When a mosquito feeds on the infected animal, the virus is transmitted to the insect where it rapidly multiplies. The virus is then passed onto the next animal or person the mosquito bites. It has been proposed that human-mosquito-human transmission can occur during RRV epidemics. One-third of all humans bitten by an infected mosquito will develop the RRV disease.

The RRV disease occurs throughout continental Australia. However, the majority of RRV infections occur in the northern states and along costal areas; in particular, the state of Queensland. Of the 4,800 cases reported annually in Australia, approximately 2,700 of these occur in Queensland. In addition to these cases, many more go unreported. Infection can occur year round, but outbreaks typically coincide with the increased mosquito activity of the wet season (between late November and the end of April). Also, areas with intensive irrigation and those near salt marches have higher mosquito populations, and, thus, tend to exhibit a higher number of RRV cases.

In addition to continental Australia, RRV is endemic to the Solomon Islands, East Timor, Papua New Guinea, and the adjacent islands of Indonesia. Epidemics have also been reported in the Cook Islands, Fiji, French Polynesia, New Caledonia, and Western Samoa.

Causes and symptoms

Many people that are infected with RRV will never develop symptoms. However, 25% to 45% of cases will develop symptoms within three days to three weeks (averaging nine days) of the infection. Symptoms will vary between patients, but typically include arthralgia, arthritis, myalgia, skin rash, fever, fatigue, headache, and swollen lymph nodes. Tingling and pain in the palms of the hands and soles of the feet can accompany these symptoms. Other, less frequent, symptoms can include general malaise, nausea, sore eyes, and sore throat.

Most patients with RRV disease (83% to 98%) experience symptoms of polyarthritis involving the wrists, knees, ankles, and small joints of the extremities. Less frequently affected joints include the elbows, toes, tarsal joints, vertebral joints, shoulders, and hips. Symptoms can range from restricted joint movement to prominent swell and severe pain. Although severe joint pain can last for only 2 to 6 weeks, over half of patients will continue to experience joint pain for 6 to 12 months after RRV infection. Symptoms typically diminish over time, but relapses are common and have been known to persist for several years. This persistent polyarthritis can lead to fatigue and myalgia, contributing to RRV diseases high morbidity.

Diagnosis

Diagnosis usually consists of serological tests to determine the presence and increase of RRV antibodies. Samples should be taken during the acute or convalescent stages of the illness. Testing will help clinicians differentiate between RRV disease and Barmah Forest virus disease, a very similar arbovirus. Virological tests can help distinguish between RRV disease and other causes of arthritis.

Treatment

No cure for RRV disease currently exists, so only its symptoms can be treated. In one of the few studies on RRV disease treatment, Cordon and Rouse (1995) found that roughly one-third of patients (36.4%) reported that nonsteroidal anti-inflammatory drugs (NSAIDS) provided them with the best symptomatic relief. In addition to NSAIDS, others patients found that rest (24.1%), aspirin and paracetamol (16.4%), or physical therapies (10.3%), such as hydrotherapy, massage, and physiotherapy, were their only source of symptom relief. Unfortunately, 20% of patients found none of these interventions effective. Health providers typically use one or a combination of these treatments for their patients. In particular, paracetamol has been found to be effective for treating the pain and fever associated with RRV disease.

Although some clinicians have found the use of oral corticosteroid useful and effective, this practice is considered unwise and unnecessary. The adverse effects associated with corticosteroids may outweigh their benefits, and may even worsen the RRV disease. More study is required on this and other treatment interventions of RRV disease.

Prognosis

Patients infected with RRV disease will fully recover within four to seven months. Although milder cases can recover within a few weeks, many cases have persisted for several years. Only the symptoms can be treated during this time, not the disease. Fortunately, RRV infection usually provides the patient with lifelong immunity to future infection.

Prevention

Prevention techniques of RRV typically coincide with measures used to avoid mosquito bites; the primary source of the virus. These include the use of insect repellant (with 5% to 20% DEET) on exposed body parts, wearing loose-fitting clothes over the limbs and torso while outdoors, using mosquito coils and/or citronella candles outdoors, and limiting outdoor activities during peak biting periods and/or in areas with high mosquito density. While camping outdoors, knockdown spray or bed netting with pyrethrum is suggested. Additional steps for reducing risk of being bitten include using screens in homes and removing mosquito-breeding areas near the home, such as uncovered water containers and old tires. Mosquito eradication programs can assist in reducing insect populations. An RRV vaccine is currently being developed.

Resources

BOOKS

Kay B.H., and J.G. Aaskov. "Ross River Virus (Epidemic Polyarthritis)". In The Arboviruses: Epidemiology and Ecology (Vol. IV), edited by T.P. Monath. Boca Raton, FL: CRC Press, 1989, pp. 93-112.

PERIODICALS

Harley, D., A. Sleigh, S. Ritchie. "Ross River Virus Transmission, Infection, and Disease: A Cross-disciplinary Review. " Clinical Microbiology Reviews 14 (October 2001): 909-932.

Harley, D., S. Ritchie, C. Bain, and A. Sleigh. "Risks for Ross River Virus Disease in Tropical Australia." International Journal of Epidemiology (January 26 2005): 1-8.

Flexman, J., D. Smith, J. Mackenzie, J. Fraser, S. Bass, L. Hueston, et al. "A Comparison of the Diseases Caused by Ross River Virus and Barmah Forest Virus." Medical Journal of Australia 169 (August 1998):159-163.

Hills, S. "Ross River Virus and Barmah Forest Virus Infection." Australian Family Physician 25 (December 1996):1822-1824.

OTHER

"Ross River Virus Infection-Fact Sheet" Australian Government- Department of Health and Ageing 〈http://www.health.gov.au/internet/wcms/Publishing.nsf/Content/health-arbovirus-pdf-fsrossriver.htm〉.

KEY TERMS

Arthralgia— Sharp, severe pain, extending along a nerve or group of nerves, experienced in a joint and/or joints.

Abrovirus viruses— Also known as arthropodborne viruses, these viruses are maintained in nature through biological transmission between vertebrate hosts and blood-feeding arthropods. Infection occurs when an infected arthropod, such as a mosquito, feeds off a vertebrate, such as a human.

Macropods— Derived from the Greek, macropod literally means "large footed." Macropods are marsupials belonging to the family Macropodidae, which includes kangaroos, wallabies, tree kangaroos, pademelons, and several others.

Myalgia— Muscular pain or tenderness, typically of a diffuse and/or nonspecific nature.

Polyarthritis— A nonspecific term for arthritis involving two or more joints, typically associated with auto-immune forms of arthritis. Symptoms usually include pain, inflammation, and/or swelling in multiple joints.