Enzootic Bovine Leucosis (EBL)

What is it?

EBL is a viral disease of cattle. In most cases, the disease will not progress beyond lymphocytosis (ie too many lymphocytes in the blood ), in which case the affected cattle will not develop clinical signs, will not suffer and there will be no loss in production. However, in some cases, the disease will develop into cancer of the lymph nodes (lymphosarcoma) and, from there, the cancer spreads into internal organs. Currently, there is no effective treatment for EBL.

What species are affected?

Cattle. Dairy cattle are more often affected than beef cattle. There is no evidence of it naturally infecting other species. It does not affect humans and any virus in the milk is destroyed by the pasteurisation process.

Is EBL present in Tasmania?

The Tasmanian dairy industry and the Deptartment of Primary Industries (now DPIPWE) have been managing an EBL eradication campaign in Tasmania since 1994. Over the past 12 years, surveillance has identified EBL-positive animals in just two Tasmanian herds. Both were animals born on the mainland and both properties were quarantined until the infected animals were culled and tests confirmed the herds EBL-free. Currently, there are no known EBL-positive herds in Tasmania.

A survey of beef herds in Tasmania in 1999 found no evidence of the disease in beef cattle.

In the period August to December 2009, Tasmania participated in a national EBL testing program (see below). All 442 of Tasmania's dairy herds were negative, which means Tasmania is considered to be EBL-free.

Why is EBL significant for Tasmania?

EBL is a notifiable disease.

The cattle that are affected but do not develop clinical signs do not appear to suffer and there is no obvious loss of production. But cattle that do develop the clinical signs can suffer considerably and will eventually die. The disease, therefore, has some welfare and productivity consequences.

There are increasing international restrictions on the trade of cattle, semen, ova and milk products from affected herds and regions. Many of our competitors in the world markets have either eradicated EBL and gained formal EBL-freedom status or are in the process of doing so. Without formal recognition of EBL Freedom, we may lose some market access or opportunities.

Under a 2008 national agreement, the dairy industries in all states are working together to get Australia formally recognised as being EBL Free (see below).

What are the clinical signs?

Most cattle with EBL will not progress beyond lymphocytosis and show no clinical signs - and indeed be healthy. But in some cases, the animal will become obviously ill as the cancer develops and then spreads from the lymph nodes to internal organs. The clinical signs will vary somewhat according to the internal organ affected. They may include paralysis (if the spine is affected), breathing difficulty and/or listlessness - and may show none of these signs until very late in the disease's progress. The first signs you are most likely to see are small lumps on the skin or in the lymph nodes just under the skin - most commonly, but not always, in the shoulder and neck area or above the udder.

It is rare to see the signs of EBL in young cattle.

How is it spread?

It can be spread from dam to calf either in utero or via the milk.

It can be spread from cow to cow by blood transfer. Risks include hyperdermic needles, dehorning equipment and rectal pregnancy tests where equipment is not changed or disinfected between animals.

The EBL eradication program

While the Tasmanian eradication program has been successful (see above), a very small number of herds were still testing positive on the mainland. In October 2008, all the State DPIs and industry bodies agreed to support a national EBL eradication campaign to clear up the few remaining infections and then move towards formal OIE (World Animal Health Organisation) EBL Freedom status for Australia as a whole.

The Tasmanian eradication campaign had been based on an intense run of bulk milk testing from 1994 to 2003. Each dairy herd was tested three times a year. Testing since 2003 has been less intense.

Under the national EBL eradication program, all states undertook an EBL testing program with a target of achieving provisional EBL freedom by the end of 2009. Tasmania's EBL testing program was completed by that date and the results showed that all 442 of Tasmania's dairy herds tested negative.

Under the testing program, herds with less than 200 cows had one bulk milk test. Where a herd was larger than 200 cows, it was broken down into sub-samples of 200 cows. Essentially, the milk from 200 cows was pooled and then tested - this is known as an "intensive milk test".

Once all states have completed their EBL testing programs, and providing all results are negative, the Australian dairy herd will have provisional freedom status. The ultimate goal of full freedom from EBL will involve each herd having one bulk milk test in each of the next three years. Providing all results in this three year period are negative, formal EBL freedom will then be recognised internationally.

The milk processors will be collecting the samples and forwarding them to the labs. As this is an Industry control program, the milk processors will accept the cost of testing. It is then up to the processor to determine how to manage that cost. Tasmania does not have a farmer funded Industry Disease Compensation fund for the EBL eradication program.

If the testing program does identify an EBL positive herd in Tasmania in the future, DPIPWE will investigate the farm to identify the individual EBL infected animals and facilitate eradication of the disease.

Biosecurity practices to minimise the risk of EBL on your property

The risk of introducing EBL into your herd is low and will get progressively lower as Australia moves towards EBL-free status. With all dairy herds around Australia being tested every year until 2012 and, so far, all test results coming back negative, the risk of you bringing EBL onto your property through cattle you have bought is very low.

The biosecurity measures you should take to prevent EBL are what you should be doing anyway - avoid transferring blood between cattle during examination or treatment. Any equipment that is capable of carrying blood from one animal to another is a biosecurity risk. Equipment such as dehorning gear, nose tongs, oral speculums and other instruments should be cleaned and disinfected between each animal. Other equipment such as needles, rectal examination gloves etc are disposable and should be properly disposed of and not be used on another animal. Although the risk of introducing EBL through the purchase of a beef bull is low, there is still a risk. This should be managed by getting any beef bulls tested before they enter the herd. EBL is known to occur in beef cattle in Northern Australia.

Further information

For more information about EBL, please contact your local vet or the DPIPWE contact listed below.

EBL is a notifiable disease. If any of your cattle show any of the clinical signs (see above), you must contact your local vet or the DPIPWE animal disease hotline 1800 675 888.


Contact

Veterinary Officer (Disease Control and Surveillance)
Debra Grull
Rundle Road
DEVONPORT TAS 7310
Phone: 03 6421 7641
Mobile: 0428 253 828
Fax: 03 6421 7666
Email: Debra.Grull@dpipwe.tas.gov.au

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