Bluetongue virus factsheet
Bluetongue disease is a viral disease that affects ruminants. Victoria is free from clinical bluetongue disease and most of Victoria, excluding one area in the north-east of the state, is located in Australia’s bluetongue virus-free zone.
What is bluetongue disease?
Bluetongue disease is a viral disease that is spread by insect vectors (Culicoides midges).
Of the 26 serotypes of bluetongue virus (BTV), 13 have been detected in Australia. Fortunately, the highly pathogenic strains associated with some severe overseas outbreaks are exotic (not present) in Australia.
Clinical signs associated with bluetongue disease tend to be most severe in sheep (and, sometimes, goats).
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 flocks in Australia.
The incubation period – from when an animal is bitten by an infected midge to when clinical signs are observed – is usually 5 to 20 days and is possibly influenced by the amount of virus transferred into the animal by the midge.
Clinical signs in sheep may include:
- fever (40°C to 41°C)
- excessive salivation and initially clear nasal discharge, which turns into thick and purulent mucus
- swelling of lips, tongue and face
- difficulty breathing
- lameness, with possible reddening of the coronary band (top of the hoof)
- diarrhoea
- rapid weight loss and a drop in production.
Mortality rates will vary according to the strain of BTV. Some strains that are exotic to Australia have mortality rates of 20% to 40% quite commonly and they can be as high as 70% in sheep.
Some animals may show signs of a swollen, bluish-coloured tongue (hence the name ‘bluetongue’). This will not always be seen and should not be relied on to diagnose bluetongue disease.
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 and the distribution of BTV in Australia is largely determined by the distribution of this insect. C. brevitarsis is generally limited to the northern and eastern parts of Australia. C. brevitarsis is not known to be present in Victoria.
BTV is usually spread to sheep (via biting midges) following amplification of the virus in cattle, so disease might not be observed for some time after the virus has entered an area. 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.
BTV does not persist in animal carcasses, animal products, outside the host or vector, on equipment or personnel, or in the environment.
What species are affected?
All ruminants are susceptible, including sheep, cattle, goats, deer, camelids and buffalo.
Cattle can carry the virus without showing any obvious signs of illness. Infected cattle provide a reservoir for the virus to be spread by biting midges.
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 do I do if I suspect BTV?
BTV is a notifiable exotic disease and any suspected cases must be reported immediately to Agriculture Victoria on the Emergency Animal Disease Watch Hotline on 1800 675 888 (24/7) or to your local Agriculture Victoria animal health staff.
What is the government’s response to BTV?
The distribution of bluetongue virus in Australia is monitored through the National Arbovirus Monitoring Program (NAMP) and involves regular testing of sentinel cattle herds, as well as trapping of insects throughout Australia. Some international trading partners will only obtain livestock for live export from BTV-free zones. By conducting surveillance under NAMP, export markets for live animals, including semen and embryos, are maintained for Australia’s BTV-free zone.
More information about NAMP can be found on the Animal Health Australia website.
If clinical disease is detected in sheep or other susceptible livestock, different responses can be implemented. The response will vary depending on where the sheep flock is located (i.e. if in a BTV-free zone or a BTV-transmission zone), and whether the strain of bluetongue virus is endemic to Australia or exotic.
Response guidelines for clinical bluetongue disease are outlined in the AUSVETPLAN Bluetongue disease Response Strategy. This strategy contains predetermined policy that has been agreed to by both the government and livestock industries. A response will aim to protect the health and welfare of susceptible livestock and minimise disruptions to international trade. A combination of strategies can be deployed, which may include:
- quarantine and movement controls for ruminant livestock in affected areas
- tracing and surveillance to determine the source and extent of infection
- supportive therapy for clinically affected livestock (there is no specific treatment available)
- controlling insect populations to help prevent further spread of disease.
Further information
PDF version of this factsheet
Download a PDF version of this factsheet: