BLUETONGUE, BOVINE - AUSTRALIA (NORTHERN TERRITORY)
A ProMED-mail post http://www.promedmail.org
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Date: Tue 29 Aug 2017 21:06
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 [July 2017], 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.
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.
"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.
Date: Thu 30 Aug 2017
From: Mark Shipp <Mark.Schipp@agriculture.gov.au> [edited]
The National Arbovirus Monitoring Program (NAMP) maps areas in Australia where bluetongue virus transmission occurs, using both sentinel herds and additional sampling of herds when mustered.
Sentinel herds are bled and tested regularly, however in very remote areas where sentinel herds are not practical, cattle are sampled during the annual muster.
Bluetongue viral transmission occurs in parts of Australia but disease has not been reported.
There is a buffer zone between the zone where bluetongue virus transmission can occur and the zone free of bluetongue virus transmission. This is called the surveillance zone and is 50 Km [31.06 mi] wide. The distance maintained between records of viral transmission and the boundary of the free zone is always maintained at a distance of 100 km [62.13] and follows property boundaries.
Yearly variation in the distribution of the main insect vector Culicoides brevitarisis means that the NAMP records some variation in the zone boundary from year to year. The map was most recently updated on [Wed 16 Aug 2017]. Detection of viral transmission immediately results in a zone expansion however zone contraction requires 2 years of negative surveillance results. The variations in the boundary are generally small and are considered routine. The NT example is confounded by changes in the management of land that have seen the amalgamation of properties. Because the zone boundary follows property boundaries this has exaggerated the zone extension. Property sizes can be extensive; up to 12 000 square km [4633.22 square miles] in some cases.
There can be a lag period observed between viral transmission and antibody detection, particularly where surveillance is based on sampling mustered animals rather than sentinel herds. This maybe where the confusion has arisen in the quoted media report. Sero-conversion was detected in winter but arose from insect activity earlier in the season.
The media report is inaccurate in relation to market access.
Recently negotiated conditions with China allow access for Australian feeder and slaughter cattle raised in areas where bluetongue virus transmission can occur. Parts of China record transmission of bluetongue virus year round and most of China (like parts of Australia) experiences times in the year where bluetongue viral transmission can occur (seasonal transmission).
The bulk of cattle in the Northern Territory are exported to markets that are endemic for bluetongue and while export conditions are applied, they are generally not trade restrictive.
The report of the zone expansion is publically available through the NAMP web site that is hosted on the Animal Health in Australia Web site.
It is certainly true that some markets require animals to be sourced from bluetongue virus free areas. This is the main reason that the NAMP program is maintained as it provides access for Australian cattle to these markets by confirming a zone free from viral transmission.
Objectives of the NAMP are:
1. Market access - to facilitate the export of live cattle, sheep and goats, and ruminant genetic material, to countries with concerns about bluetongue, Akabane and bovine ephemeral fever (BEF) viruses
2. Bluetongue early warning - to detect incursions of exotic strains of bluetongue virus (BTV) and vectors (Culicoides species biting midges) into Australia by surveillance of the northern BTV epidemic area.
3. Risk management - to detect changes in the seasonal distribution in Australia of endemic bluetongue, Akabane and BEF viruses and their vectors, to support livestock exporters.
Chief Veterinary Officer (Australia)
OIE Delegate (Australia)
Vice-President OIE Assembly
7 London Cct, Canberra ACT 2600
GPO Box 858,
[In previous situations the line has been moved to reflect the seroconverstion, not actual disease discoveries. I reached out to Dr Schipp with some questions. Below are our question and answers:
ProMED-mail moderator (hence PMM): It appears this is a standard line movement based on seroconverstion - without actual disease? Could you clarify for me please?
Dr Schipp: Yes this is a regular adjustment of line to reflect seroconversion without clinical disease.
PMM: Also the way this article is written is a bit confusing to me. As it is late August/1st of September, so I am thinking you may in late winter/early spring, yet the article above talks about frosts in the winter?
Dr Schipp: The hope expressed by Dr Saville is that the frosts currently being experienced in the central Austral winter will deplete the number of _Culicoides_ able to over winter to then become abundant in the spring and summer.
ProMED-mail thanks Dr Schipp for his promt reply and for taking the time to clarify issues regarding the surveillance line.
Information for understanding Bluetongue.
Bluetongue virus (BTV) can and does affect cattle.
The disease is caused by an orbivirus belonging to the family _Reoviridae_. There are 25 serotypes of bluetongue virus and 10 of these have been isolated in Australia. Orbiviruses are insect-borne viruses (arboviruses) transmitted by _Culicoides_ midges. Many other non bluetongue orbiviruses are also endemic in Australia.
Bluetongue is an insect-borne, viral disease that can affect sheep, goats, deer, and cattle. Sheep are the most seriously affected species; clinical disease and mortalities occur and production and trade losses may result. Most infections in cattle are unapparent.
A number of bluetongue serotypes are present in Australia, but the severe clinical disease seen in other countries has not occurred here. Disease has been produced in experimentally infected sheep with some serotypes present in Australia.
Bluetongue virus serotype 1 was 1st identified in Australia in 1975 from trapped insects in the Northern Territory (NT) but despite its long-term presence, it has not caused any clinical disease. Since that time 9 more serotypes have been isolated in the NT. The distribution of BTV in Australia has been monitored in the National Arbovirus Monitoring Program (NAMP) for many years and the zones of BTV virus transmission and freedom are mapped and updated regularly on the Animal Health Australia website. - Mod.TG
A HealthMap/ProMED-mail map can be accessed at: http://healthmap.org/promed/p/292.]