BLUETONGUE VIRUS is an arbovirus that is spread by biting midges. After biting sheep or cattle that are carrying the virus, the midge (Culicoides spp) can then inject infected blood into other ruminants and so pass on the virus. There are different serotypes of the virus that can cause varying severity of clinical disease in ruminants as seen in some overseas countries.
Sheep are the most severely affected species and can show signs of depression, swollen lips, tongue, gums and face, cyanosis (blueness) of tongue, lameness, inability to stand and respiratory difficulty.
Despite the fact that there are 12 serotypes found endemically in northern Australia there have not been any clinical cases in Australian livestock, with the exception of two minor incidents in sheep in Darwin in 1989 and 2001.
The BTV zone in northern Australia extends from the north of Western Australia, across the Northern Territory through most of Queensland and down the north-east coast of NSW. This zoning is internationally recognised and is supported by the National Arbovirus Monitoring Program (NAMP). As the virus is spread by insect vectors, the distribution of BTV can vary depending on seasonal conditions. So why is it a concern?
A number of countries that import Australian livestock require that they are sourced from a BTV-free zone and therefore animals bred within the BTV zone would be excluded from export to those countries.
Unfortunately, in October some heifers on a property at Bamawm (south of Echuca) were found to be positive for BTV while undergoing routine blood tests for export.
As a result, the BTV-free status of Victoria has been put in question. In response, Agriculture Victoria has established a Temporary BTV Transmission Zone within a 50 km radius of the property and a further 50 km buffer zone.
While this is in place any animals within that zone are ineligible for export to countries with the requirement of originating in a BTVfree zone. The department then instigated surveillance by bleeding 2500 cattle in more than 100 mobs within that zone to establish the true prevalence of the virus.
At the time of writing we are still awaiting the results of testing and the temporary zoning has been extended to December 13.
The main reason for the surveillance is to safeguard Victoria’s BTV-free status, in order to keep export markets open. There is no concern about the health/production of the animals and there is no risk to humans from this virus.
There is no restriction on movement of animals from this zone within Victoria or to other parts of Australia — the significance is purely for maintaining access to those export markets.
Hopefully the results of the testing will show that the virus is not established in this area, which would be highly unlikely due to the lack of the required insect vectors. Once the ‘zone of possible transmission’ has been lifted animals from that area will once again be eligible for those export markets.