Bluetongue virus is a reportable disease in WA
Bluetongue virus is present in a monitored zone across northern and parts of eastern Australia.
Clinical bluetongue disease (when the virus causes clinical signs of infection in an animal) is uncommon in Australian sheep and has not been reported in other susceptible animal species in Australia.
About bluetongue virus
Bluetongue virus is an arbovirus that affects ruminants. Arboviruses are a group of viruses that are transmitted by infected insects. Bluetongue virus is spready by a specific species of biting midge, Culicoides sp. Six of the known 180 species of Culicoides sp. capable of spreading bluetongue virus are present in Australia.
Bluetongue is not transmitted directly between animals. Bluetongue does not affect people.
Of the 26 serotypes of bluetongue virus, 13 have been recorded in a monitored zone across northern Australia and in parts of eastern Australia. These include serotypes 1, 2, 3, 4, 5, 7, 9, 12, 15, 16, 20, 21 and 23. In Western Australia serotypes 1, 16, 21 and 23 are consistently detected throughout parts of the Kimberly. Serotypes 3, 4, 5, 7 and 20 have also been recorded. Fortunately, the highly pathogenic strains associated with severe disease overseas are exotic to Australia.
There is no effective treatment available for bluetongue virus. Vaccines exist overseas but are not approved for use in Australia.
Australia’s recognised bluetongue virus zones are monitored regularly via the National Arbovirus Monitoring Program (NAMP). Some countries that import live sheep and cattle are concerned about the presence of bluetongue viruses in Australia. The National Arbovirus Monitoring Program provides an early warning system through surveillance within the bluetongue virus zone for incursions of exotic strains and seasonal distribution of vectors to help predict the likelihood of arboviruses in particular areas.
A current map of the bluetongue virus zone in northern and parts of eastern Australia is available on the Animal Health Australia website. This zone map is based on World Organisation for Animal Health (WOAH) guidelines and defines the area where bluetongue virus is considered to occur, and the area where no occurrence has been detected for at least two years.
In Australia, clinical disease is rare in sheep and has never been reported in other susceptible animal species.
In sheep, clinical signs can be variable ranging from acute to mild. British breeds and Merinos are more susceptible. Signs can include:
- fever which may last a week
- reddening of the lining of the mouth and nose with the possible development of red or purple haemorrhages
- excessive salivation
- clear nasal discharge which may become thicker with mucous and pus and blood-stained
- swelling of the lips, tongue and head
- death rates of 20 to 40%, but may be as high as 70%
- ulcers on the gums, cheeks and tongue
- stiffness, lameness and arched back stance
- foot lesions characterised by reddening around the coronary band (top of the hoof).
The clinical feature that gives the disease its name, a cyanotic (blue) tongue only occurs occasionally.
Goats are less commonly and less severely affected than sheep.
Although cattle and buffalo are considered to be the principal hosts of bluetongue virus, clinical disease is not generally observed in these species.
Severe disease and mortalities have occurred in white-tailed deer in the United States.
Camelids may be affected with bluetongue virus, but clinical disease has only been recorded in South American camelids.
The incubation period from an animal being bitten by an infected midge to clinical signs is 5 to 20 days and is possibly influenced by the amount of virus transferred into the animal from the midge.
Some endemic diseases can present similarly to bluetongue virus such as photosensitisation and scabby mouth.
Exotic diseases such as foot and mouth disease, epizootic haemorrhag disease and sheep pox, as well as reportable diseases such as footrot can also present similarly to bluetongue virus.
Bluetongue virus is transmitted in the saliva of the infected Culicoides sp. biting midge. Cattle and buffalo are considered to be the principal hosts. The virus is usually spread to sheep (via the biting midges) following amplification of the virus in cattle or buffalo. Infected animals can only transmit the virus to a competent biting vector for several weeks after the initial infection. Cattle can remain infective (viraemic) for up to 50 days and 20 days in sheep.
Bluetongue virus only occurs where there is a suitable environment for the vector. The Culicoides sp. biting midge requires some moisture, warmth, vegetation and cattle dung to persist and so mainly occurs in tropical and subtropical regions of the world. Bluetongue virus spread is most likely to occur when the Culicoides midge is active in late summer and autumn.
In recent years bluetongue virus has been detected in northern European countries, including England. The virus has been able to adapt to new Culicoides sp. vectors capable of over-wintering in temperate climates.
The bluetongue virus does not survive outside the vector species or susceptible ruminant hosts.
The bluetongue virus does not persist in the environment, but infected vectors can be carried over long distances by wind.
The most important way to protect Australia from bluetongue virus is by restricting sheep from regions where the virus and its vectors occur (such as in the Kimberley). In WA the keeping of sheep in the Kimberley is strongly discouraged and producers are requested to contact DPIRD for advice.
If moving cattle from within the bluetongue zone to properties outside of the zone and into areas where the Culicoides sp. biting midge sometimes occur (such as the southern Kimberley and the Pilbara), only move them when the midge is not likely to be active (preferably late winter or early spring).
Bluetongue virus will spread only where there is a suitable vector, however, controlling the vector in extensive farming systems is not considered possible.
How to report bluetongue virus
If you suspect bluetongue virus, see signs of disease or death consistent with bluetongue virus in your flock or herd, you must report it. There are 3 ways you can do this: