Bluetongue virus
Bluetongue is a viral disease caused by Bluetongue virus (BTV) and is spread by biting insects such as Culicoides midges. Nine of the twenty-four known strains (serotypes) of BTV have been identified in Australia. Many of the strains of BTV that can cause severe disease are exotic to Australia.
Victoria is a Bluetongue virus (BTV) transmission-free area.
A temporary precautionary zone was in place in 2017 in northern Victoria however this was lifted on 6 December 2017 and all movement restrictions under Victorian legislation were removed following extensive testing.
Where BTV is found in Australia
Some strains of BTV are endemic (present) in northern and parts of north-eastern Australia, so national freedom from BTV is not possible.
Victoria remains a BTV transmission-free area.
Australia has a recognised BTV zone and monitoring of BTV infection is conducted regularly by the National Arbovirus Monitoring Program (NAMP). This program supports national BTV surveillance to monitor the location, spread and strains (serotypes) of BTV that are circulating across Australia.
There is a map on Animal Health Australia website showing the current BTV transmission zones.
Animals at risk
Ruminants such as sheep, goats, cattle, buffalo and deer are susceptible to BTV.
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. Viraemic (infected) cattle provide a reservoir for the virus to be spread by biting midges.
Clinical signs of Bluetongue virus disease
Clinical signs associated with bluetongue virus are usually only seen in sheep, (rarely goats) and can be lethal.
The incubation period from an animal being bitten by an infected midge to clinical signs is usually 4 to 7 days.
Clinical signs include:
- fever (40 to 41°C)
- lameness
- reddening around the coronary band (top of the hoof)
- nasal discharge
- swelling of the lips, tongue and head.
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 upon to diagnose Bluetongue virus disease.
Death rates of 20 to 40 per cent are common but may be as high as 70 per cent in sheep.
Any health concerns in your livestock should be reported immediately to Agriculture Victoria on the Emergency Animal Disease Hotline, 1800 675 888 or your veterinary practitioner.
BTV and people
BTV cannot infect people.
There are no food safety issues, and meat and dairy products are safe to consume.
Market implications of BTV
Australia’s livestock export trade provides significant economic benefits to rural communities and the viability of the Australian sheep, goat, beef and dairy cattle 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 areas free of BTV so it is important Victoria maintains our BTV-free status to maintain these lucrative export markets.
Detection of BTV-exposed cattle in Victoria (2017)
In October 2017, pre-export testing of cattle in Victoria detected evidence of previous exposure to BTV in several cattle and further testing was required to determine if Victorian-bred cattle were at risk. There were no signs of clinical disease in any animals at any time during the investigation.
A 100-kilometre radius temporary precautionary BTV zone was established as a precautionary measure. This remained in place while investigations and surveillance were conducted to establish whether BTV was present in Victorian born and raised cattle and to determine if BTV had transmitted within the local area.
The zone was important for providing assurances to international trading partners such as China on BTV area freedom and supporting the livestock export industry.
The temporary Bluetongue virus (BTV) zone in northern Victoria was lifted on 6 December 2017 after the results of extensive testing demonstrated no further detections of BTV virus..
Victoria remains a BTV transmission-free area.