Bluetongue virus
Bluetongue disease is a viral disease caused by bluetongue virus (BTV) and is spread by biting insects Culicoides midges. Of the 26 strains BTV globally, 13 have been detected in Australia. Fortunately, the strains of BTV that can cause severe clinical 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. 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 associated with bluetongue disease are usually only seen in sheep (and sometimes goats) and it can be fatal.
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.
Clinical signs include:
- fever (40°C to 41°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 of 20% to 40% are common overseas but they may be higher in sheep.
Suspicion of bluetongue disease in your livestock should be reported immediately to Agriculture Victoria on the Emergency Animal Disease Hotline, 1800 675 888, or to 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 strains of BTV are endemic (always present) in northern and eastern Australia, so national freedom from BTV is not possible.
Australia has recognised BTV zones and monitoring the distribution of BTV is conducted regularly in accordance with the National Arbovirus Monitoring Program (NAMP). This program supports national BTV surveillance to monitor the distribution and types/strains of BTV that are circulating throughout Australia.
A map showing the current BTV transmission zones is available on the Animal Health Australia website.
The impact of BTV on international markets
Australia’s livestock export trade 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. Livestock in the recently declared (July 2024) BTV-transmission zone in north-eastern Victoria may be excluded from live export to some countries. Livestock export companies can advise producers of their eligibility to sell livestock to specific international markets.