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This article was published in 2000
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Enznotic Bovine Leukosis In New South Wales
Tony Ross, NSW Agriculture
PURPOSE
EBL is caused by the oncogenic bovine leukaemia retrovirus. It is present within infected B lymphocytes and therefore present in meat and milk. It is easily inactivated by pasteurisation and cooking and there is no evidence that it can infect man. However it will cause lymphosarcomas in approximately 50 % of sheep challenged with the virus. Most developed countries have eradication programs based on consumer concerns. Most countries require Australia to only sell live animals, embryos, semenetc., which are free of BLV.
PROGRESS TO DATE
NSW began to eradicate EBL in dairy cattle in 1993. At that time 603 of 1975 dairy herds were infected. By September 2000 the total number of dairy herds was 1620 with only 18 herds remaining infected and 26 provisionally clear.
ERADICATION
The target of reaching Provisional Freedom which is defined as having no known infected herds, at least 99.8% of herds monitored negative or tested negative and all herds under surveillance, may be reached by early 2002. However a major threat to achieving the target is the massive numbers of cattle predicted to move between herds during the post-deregulation shakeout. Industry funding to subsidise laboratory testing has been an enormous help to the program but is coming to an end.
The costs of bulk milk testing will be transferred to individual milk processors from November 2000. Access to remaining herd testing funds will be rationed and may be exhausted by early 2001. A further threat to the program has been the dismembering of the NSW Dairy Corporation, which supplied a number of administrative and technical services. It coordinated address lists and bulk milk sampling throughout the state. This now has to be done separately within each of the 8 processor companies.
POST ERADICATION
After eradication NSW dairy factories or groups of factories can apply for Provisional Free status under the Australian Standard Definitions and Rules for EBL. This requires:
1 continuing surveillance of all herds for EBL via bulk milk testing.
2 permitting only clean herds to enter the industry.
3 quarantining and managing infected herds back to Tested Negative.
It is the third requirement that is managed by District Veterinarians in NSW. After 3 years of meeting the Provisional Free criteria factories may apply for Free status.
OTHER STATES
All factories and groups of factories supplied by dairy herds in Western Australia, South Australia and Tasmania are reported to meet Provisionally Free criteria. Queensland has 29 infected herds, 9 provisionally clear and 33 lapsed herds. However Victoria which has approximately 8000 dairy herds, has at least 498 herds with evidence of infection and is several years away from approaching Provisional Freedom. In the meantime there are 2 potential dangers when dealing with Victorian dairy cattle. The first is that infected herds are not under quarantine. Very considerable numbers of animals from infected herds could end up in NSW herds requiring the herd status to be downgraded to Infected, quarantine imposedetc. The status of Monitored Negative is awarded on lesser criteria than in NSW with a consequent increase in risk. DVs are asked to make their dairy fanner clients aware o the risks and recommend appropriate precautions.
Acknowledgements
The tremendous progress in approaching eradication has been achieved through co-operation and hard work between owners, DVs and the testing laboratories of NSW Agriculture. Particular mention should be made of the work of the EBL Registrar Richard Zelski for collating and monitoring herd statuses of all dairy herds in NSW and the supportive contributions of the NSW Cattle Compensation Fund, the NSW Dairy Corporation and the NSW EBL Steering Committee.