Bluetongue virus
Bluetongue disease is an insect-borne viral disease of ruminant animals caused by bluetongue virus (BTV). The disease is spread by some biting midges of the genus Culicoides. Of the 27 BTV serotypes globally, 13 have been detected in Australia. Fortunately, the strains of BTV that can cause severe disease in livestock are exotic (not present) in Australia.
Bluetongue disease
All ruminants, including sheep, goats, cattle, alpacas, buffalo and deer, are susceptible to BTV.
Of the domestic species, sheep are the most severely affected. Sheep (and sometimes dees) are usually the only species that develop clinical signs – and the disease can be fatal. Cattle can carry the virus without showing any obvious signs of illness. Viraemic (infected) cattle provide a reservoir for the virus to be spread by biting midges.
The incubation period – from when an animal is bitten by an infected midge to when clinical signs are observed – is usually 4 to 8 days.
Clinical signs include:
- Fever (40 °C to 42 °C)
- Swelling of the lips, tongue and head
- Nasal discharge
- Lameness
- Reddening around the coronary band (top of the hoof)
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 upon to diagnose bluetongue disease.
Death rates in sheep of 30% to 70% have occurred overseas.
If you suspect bluetongue disease in your livestock, report it immediately to Agriculture Victoria on the Emergency Animal Disease Hotline on 1800 675 888 or contact your veterinary practitioner.
BTV and public health
BTV cannot infect people.
There are no food safety issues, and meat and dairy products are safe to consume.
Monitoring the distribution of BTV in Australia
Some serotypes of BTV are endemic (always present) in northern and eastern Australia, so national freedom from BTV is not possible.
Australia has recognised bluetongue virus (BTV) zones. The distribution of BTV is regularly monitored through the National Arbovirus Monitoring Program (NAMP). This national surveillance program tracks where BTV occurs and identifies the virus serotypes of BTV that are circulating across Australia.
A map showing the current BTV transmission zones is available on the Animal Health Australia website.
The impact of BTV on international markets
Export of Australian livestock provides significant economic benefits to Victoria’s livestock industries. Victoria’s reputation for high health status livestock plays a key role in accessing many of these markets.
Some international countries only source livestock from BTV-free zones.
In 2024 a BTV transmission zone was declared in eastern Victoria. Livestock located in this zone may not be eligible for export to some countries. Export companies can advise producers about eligibility requirements for specific international markets.