Approximately 20 new properties within Central Australia and the Barkly now fall within the bluetongue virus zone within the Northern Territory, according to the Department of Primary Industry.
Changes to the zone, introduced last month, mean 10 of those additional properties are within the transmission zone, and 10 within the surveillance zone.
Bluetongue is an insect borne, non-contagious viral disease, and the changes mean properties affected will not be able to export to a number of markets that have restrictions in place, such as China and Turkey.
Peter Saville, senior veterinary officer in Alice Springs with the Department, said in his 14 years working in the area, the line was the lowest he had ever seen it.
"What we found is that a number of properties north of the Alice Springs districts have had cattle which have seroconverted, which means that they've been exposed to the bluetongue virus, and those properties are much further south than they normally are."
Weather to blame
According to Mr Saville, the change earlier in the year was due to a summer of high temperatures and high rainfall, resulting in the increased number of insects.
"It is insect movement that controls this, and as such there's not a lot we can do, so we just have to wait and see, we can't speculate on what might happen," he said.
"For the first time we actually have Alice Springs district properties which are now in the zone of possible transmission."
Mr Saville said ownership changes could affect zoning.
"One of the things that has contributed to this is a lot of properties have amalgamated their pics [property identification codes] because they're now under one ownership, and that means that even if part of their property is in a zone then the whole of the property is regarded as being in that zone."
Fluid line movement
However Mr Saville said the line could once again move north depending on weather.
"What we hope now is after the frosts this winter there will be less insect activity in the coming Summer and the line will move north again.
"We wait until the end of summer, the end of the transmission season, and then we go out and test a number of properties to find out if there's been any evidence of viral activity.
"Once those results are in, the NAMP [National Arbovirus Monitoring Program] committee meets and decides where the blue tongue line is going to go, and where the limits of the zones are."
Mr Saville said producers should visit the Animal Health Australia website if they want more information about the changes, and contact their livestock agent.
