The Barmah Forest virus (BFV) was first isolated in 1974 from Cx. annulirostris mosquitoes collected in the Barmah Forest near the Murray River in northern Victoria, and simultaneously from mosquitoes collected in southwest Queensland. It has also been isolated from numerous other mosquitoes including the coastal species Oc. vigilax and Oc. camptorhynchus, which have a salt marsh habitat, and from the midge Culicoides marksi in the Northern Territory. Subsequently, BFV has been detected in most parts of mainland Australia, and serological surveys indicate that it causes widespread human infection

Identification

Clinical features

Similar to Ross River virus (RRV) disease, symptoms include fever, arthritis, arthralgia and rash, but with BFV disease the rash seems to be more common and more florid. Similar to RRV disease, there is a high subclinical rate of infection and a low disease rate in children. Recovery usually occurs within several weeks but lethargy, arthralgia and myalgia can persist for over six months. Confusingly, outbreaks of BFV disease sometimes occur concurrently with RRV disease.

Method of diagnosis

Serology shows a significant rise in antibody titre to the BFV. The virus may be isolated from the blood of acutely ill patients. Virological tests are necessary to distinguish BFV disease from other causes of arthritis.

Laboratory evidence

isolation of BFV from clinical material; or
detection of BFV by NAT; or
a significant rise in IgG to BFV; or
detection of BFV-specific IgM

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Incubation period

Incubation period appears to be 7 to 10 days.

Public Health Significance and Occurrence

Since 1988, BFV disease has been reported in Western Australia, Queensland, New South Wales, the Northern Territory and Victoria.

Reservoir

Like RRV disease, BFV disease appears after heavy rains which encourage the breeding of their mosquito vectors. BFV antibodies have been found in kangaroos, cattle, horses and sheep on the south coast of New South Wales.

Mode of transmission

It is transmitted by mosquitoes, with Culex annulirostris being the major vector in inland areas, whilst Oc. camptorhynchus and Oc. vigilax are the major vectors in coastal regions.

Period of communicability

There is no evidence of transmission from person to person.

Susceptibility and resistance

Infection with BFV probably confers life-long immunity.

Control Measures

Preventive measures

BFV infection can be prevented by:

Mosquito control measures.
Personal protection measures (long sleeves and mosquito repellents).
Avoidance of mosquito-prone areas. Vectors usually bite at dusk and dawn.

Control of case

Treatment is symptomatic with rest advisable in the acute stages of the disease. Presently, there is no vaccine available commercially to protect against BFV disease

Control of contacts

Unreported or undiagnosed cases should be sought in the region where the patient had been staying during the incubation period of their illness. All family members should be questioned about symptoms and evaluated serologically if necessary.

Control of environment

To reduce/prevent virus transmission, interruption of human/mosquito contact is required by:
- reduction of the vector mosquito population
- avoidance of vector contact (personal protection/education)

Outbreak Measures

Conduct a mosquito survey to determine the species of the vector mosquito involved. Identify their breeding places and promote their elimination.
Promote the use of mosquito repellents for persons exposed to bites because of their occupation, or other reasons.
Identify the infection among animal reservoirs, for example, kangaroos, farm and domestic animals.

International Measures

Airport vector control in Australia and Papua New Guinea may be necessary to prevent spread from endemic areas to other countries where local vectors (for example, Aedes polynesiensis) may transmit the disease.

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