Bluetongue
March 2018


What is Bluetongue?
Bluetongue is a viral disease of ruminants spread by biting insects called midges or sandflies.

There are at least 26 strains (serotypes) of the virus and 12 of these have been identified in Australia. 

Australia ’has the virus but not the disease’ because the strains are largely confined to the northern cattle production areas, and although these strains infect cattle they don’t cause disease. 

The strains can cause moderate disease in sheep but the major sheep production regions of Australia don’t overlap the Bluetongue zone.

How is it spread?
Bluetongue virus (BTV) is spread by some species of biting midges, Culicoides spp. or sand flies. Midges can’t fly very far but can be spread long distances by wind under favorable conditions.

Wind spread is how new strains of the virus enter Australia from Indonesia and Papua New Guinea, and how the virus spreads in Australia in the Bluetongue zone.

Infected animals also can spread the disease. The virus needs both a susceptible sheep or cattle population and specific midge species capable of transmitting the virus to spread.
 
What are the signs?
BTVs vary in their ability to cause disease.  Strains in Australia are not as pathogenic as strains in Africa and Europe, showing no clinical signs in cattle but capable of causing disease in sheep.

The clinical signs seen during an outbreak will depend on the BTV strain and type of sheep affected. European breeds, especially merinos are highly susceptible, while some African or breeds like Damaras show little if any clinical signs. 

BTV signs in sheep may include:
► depressed off food
► swollen lips, tongue, gums and face - the blue tongue, which the virus is named after, can be rare or not be present at all
► lameness or inability to stand - sheep develop a blue line at the coronary band which is prominent when feet are wet
► pneumonia and/or labored breathing
► mortalities, depending on the BTV strain. 

Monitoring

BTV is one of the vector borne viral infections tracked by the National Arbovirus Monitoring Program (NAMP), which monitors sentinel herds and insect traps for evidence of viral transmission. 

The distribution of the Bluetongue zone varies year-to-year due to climatic conditions and the distribution of specific midge vectors that require wet warm conditions. 

The limit of BTV transmission in Australia is defined as the area in which no viral transmission has been detected for the past two years.

The current Bluetongue Zone Map can be seen at the Animal Health Australia website, and is subject to change without notice.

Export markets
Some live export markets are sensitive to importing livestock from areas which have active BTV infections. Although these countries may have BTV, the strains may be different.

Some of these importing countries will not import animals from Australia’s Bluetongue zone until they have been in the Bluetongue free zone for a minimum of 60 days. Import requirements vary from country and change without notice.

Bluetongue in Victoria
In 2017 there was evidence of previous exposure (antibodies) to BTV detected in several cattle during pre-export testing.

None of the animals had active BTV infections.  As a consequence of initial testing, part of northern Victoria was designated as a Bluetongue zone, with a 100km buffer around the farm where the animals had been located.

Subsequent investigation showed that at least some of these animals came from the Bluetongue zone in New South Wales.

Surveillance and further investigation of animals in a 5km area around the initial site showed no evidence of active transmission of BTV in Victoria, but there was evidence of previous exposure in a small number of animals. 

As a result of this surveillance, the temporary Bluetongue zone was lifted in early December 2017.

For further information, please contact Livestock Health & Biosecurity VICTORIA on 1300 020 163 or lhbv@vff.org.au.

Further links
Bluetongue Virus, Agriculture Victoria

Bluetongue, Department of Primary Industries New South Wales

National Arbovirus Monitoring Program, Animal Health Australia

Bluetongue Zone Map, Animal Health Australia


Author: VFF, original version published March2018. Disclaimer: The Victorian Farmers Federation (VFF), its partners, agents and contractors do not guarantee that this publication is without flaw and do not accept any liability whatsoever for any errors, defects or omissions in the information provided. This publication is intended for general information purposes only and does not constitute financial, legal, investment, production or marketing advice. The VFF excludes all liability for any loss or damage of any kind arising in relation to this publication including any reliance on the information contained herein.


Take Home Message

► Bluetongue virus (BTV) exists in well-defined zones in northern Australia.
► There is no active BTV infection in Victoria.
► Some export markets are sensitive to BTV and livestock going to these markets are pre-screened for the virus.

 
You can download the 'Bluetongue Fact Sheet' from the link below
Bluetongue Fact Sheet
(Adobe PDF File)