Barmah Forest virus

Barmah Forest virus (BFV) disease is the second most common arbovirus after Ross River virus (RRV) in the Northern Territory (NT). It is characterised by painful or swollen joints lasting from days to months.

Symptoms usually settle by themselves.

How it is spread

BFV infection cannot be spread from person to person. The virus is transmitted to humans by the bite of an infected mosquito.

The mosquitoes present in the NT that can spread the virus are Aedes vigilax (salt marsh mosquito), Culex annulirostris (common banded mosquito), Aedes normanensis (flood water mosquito) and Aedes notoscriptus (backyard mosquito).

Many people, particularly children, even if bitten by an infected mosquito, do not develop any symptoms of the disease.

Where and when the virus is found

BFV was first isolated in northern Victoria and has been detected in most parts of mainland Australia.

In the NT, the main risk season is from December to May inclusive with the highest risk period usually in February when large numbers of mosquitoes result from either high tides or increased rainfall.

Humid conditions enable mosquitoes to live longer, which allows more chance for a mosquito to pick up a virus from an animal and to live long enough to pass it on to humans.

Since 1992 there have been between 11 and 130 cases reported annually in the NT.

Symptoms

Symptoms vary from person to person and most commonly appear within 3 to 11 days after being bitten.

Although the symptoms of BFV are similar to those of RRV disease the disease is generally milder. Symptoms include painful (sometimes swollen) joints and muscle and tendon pain. The most commonly affected joints are the ankles, fingers, knees and wrists.

Other symptoms include a raised red rash affecting mostly limbs and trunk (this may be more florid than the rash of RRV), fever, fatigue, and headache.

Fever, nausea and the skin rash usually disappear within the first 1 or 2 weeks of illness. In a minority of cases lethargy, joint, muscle and tendon pain may last for over 6 months.

Symptoms subside eventually and leave few or no after-effects. It is not possible at present to say how long an individual person will take to get better.

As a rule, once you have had BFV once, you will not get it again.

Children tend to have infection without symptoms or experience milder symptoms of shorter duration than adults.

Treatment

BFV infection is diagnosed by a blood test. There is no vaccine to prevent BFV infection, and there is no medical cure for the disease.

Medical treatment is aimed at easing joint pains and swelling, and minimising fatigue and lethargy. For some people, simple painkillers like aspirin or paracetamol are sufficient. Others will require stronger medications to ease the inflammation.

Emotional stress, physical fatigue and alcohol may cause symptoms to worsen or to last longer.

Prevention

Try to reduce the number of places on your property where mosquitoes can breed.

Any pools of water, even if tiny, can provide breeding sites for mosquitoes.

The only protection from BFV is to avoid being bitten by mosquitoes.

Personal protective measures

• stay indoors when mosquitoes are most active, from just before, until 2 hours after sunset
• ensure flyscreens in houses or caravans are in good condition
• if camping out sleep in a mosquito-proof tent or under a mosquito net. Repellents only protect against mosquito bites for up to four hours, not all night
• avoid scents on the body, e.g. perfume, deodorants, and sweat, since these can attract mosquitoes
• use personal repellents containing DEET, picaridin or PMD (extract of lemon eucalypt) on areas of exposed skin in combination with protective clothing
• use electric insecticide devices using repellent treated pads in indoor or enclosed areas
• use mosquito coils, or candle heated or gas operated devices using insecticide treated pads for patio and veranda or relatively sheltered or low wind outdoor situations.

For more information on protection measures go to protecting yourself against mosquitoes.

Information for health professionals

To find out more go to the NT Health website.

Contact

For more information contact your nearest Centre for Disease Control.