Bluetongue virus factsheet
Bluetongue is a non-contagious viral disease of ruminants spread by biting midges. Most of Victoria is a bluetongue virus (BTV) transmission-free area. Note, though, that in 2024 a BTV serological detection in a New South Wales National Arbovirus Monitoring Program (NAMP) cattle herd resulted in the BTV transmission buffer zone crossing into a small area of east Gippsland in Victoria (view a current NAMP zone map).
What is bluetongue virus (BTV)?
Bluetongue virus is a virus that causes an illness in livestock called ‘bluetongue’. Clinical signs can include inflammation of the mucous membranes, oedema and haemorrhages, which vary in severity. Of the 27 serotypes of bluetongue virus, 13 have been detected in Australia. The highly pathogenic strains associated with some overseas outbreaks are exotic (not naturally present) in Australia.
BTV does not persist in animal carcasses, animal products, outside the host or vector, on equipment, on personnel or in the environment.
The distribution of BTV in Australia is monitored through the National Arbovirus Monitoring Program (NAMP) and involves insect collection and regular testing of cattle herds across Australia.
How is the virus spread?
The virus is transmitted to ruminant animals by biting midges (Culicoides midges). To date, the biting midge Culicoides brevitarsis has been considered the most important carrier of BTV; other Culicoides species, such as C. wadai, C. fulvus and C. actoni, also act as vectors in Australia. The distribution of BTV in Australia is largely determined by the distribution of these insects, which are not known to be present in Victoria.
Signs of disease (mainly in sheep) occur 4 to 8 days after being bitten by an infected midge. As cattle don't usually exhibit any signs of infection, but can amplify the virus, disease may not be detected until sheep (or deer) are infected. Infected animals may remain infective (viraemic) for up to 60 days. An insect vector spreads the virus by biting a viraemic animal and then transferring the virus to other animals it feeds on.
What species are affected?
All ruminants are susceptible, including sheep, cattle, goats, deer, camelids and buffalo.
Sheep can experience severe disease, with breeds such as Merinos and British breeds being most susceptible.
Cattle can carry the virus without showing any obvious signs of illness.
Can the virus spread to humans?
No, BTV cannot infect people.
There are no food safety issues, and meat and dairy products are safe to consume.
What are the clinical signs of Bluetongue Virus?
Until recently, clinical disease had only been reported in Australia in 2 minor incidents involving sheep in Darwin in 1989 and 2001.
Clinical disease has more recently (between 2022 and 2024) been reported in sheep in Queensland and NSW. This is the first time clinical bluetongue has been reported in commercial sheep flocks in Australia.
Sheep are often the most severely affected species and may present with a range of clinical signs.
Clinical signs may include:
- fever (40°C to 41°C)
- excessive salivation and initially clear nasal discharge, turning thick with mucus and pus
- swelling of lips, tongue and face and breathing difficulties
- profuse diarrhoea
- lesions on the feet, with possible reddening of the coronary band (top of the hoof)
- rapid weight loss and drop in production (abortions and wool break in sheep)
- death – mortality rates in sheep of 30% to 40% are common but can be as high as 70%.
Some animals may show signs of a swollen, blueish-coloured tongue (hence the name ‘bluetongue’). This will not always be seen and should not be relied on to diagnose bluetongue virus.
What do I do if I suspect BTV?
BTV is a notifiable exotic disease. Any suspected cases must be reported immediately to Agriculture Victoria on the Emergency Animal Disease Hotline on 1800 675 888 (24/7) or to your local Agriculture Victoria animal health staff.
How can I reduce the risk of exposure?
BTV does not infect or persist on people so there are no specific PPE requirements. However, good hygiene practices are recommended when handling animals.
In general, it is also good practice to change clothing and wash footwear between handling animals on different properties.
How can I reduce the risk of spread?
BTV is spread through biting insects or management practices that involve penetrating the skin, such as vaccination and blood collection. Infected animals should be kept isolated.
Insecticide can be applied to reduce insect numbers and minimise further spread of the virus.
To minimise the risk of spreading the virus through management practices, avoid sharing needles between animals when injecting and thoroughly wash and decontaminate other equipment between animals.
What is the government’s response to BTV?
The government’s response to an outbreak of BTV will aim to eliminate clinical disease and minimise economic impacts. A combination of strategies can be deployed, which may include:
- quarantine and movement controls for ruminant livestock in declared areas
- treatment and husbandry procedures to control insects, minimise health and production effects and provide animal welfare relief
- tracing and surveillance to determine the source and extent of infection.
Further information
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