Bovine Leukosis

What is bovine leukosis?

Bovine leukosis, also known as bovine leukemia, is an infectious disease of cattle. It is caused by the bovine leukemia virus (BLV).

BLV is most commonly found in dairy cattle. Infections have also been found in buffaloes and capybaras. Sheep can be infected; however the infection does not spread naturally to sheep.

Is bovine leukosis a risk to human health?

No. There is no human health risk associated with BLV.

What are the clinical signs of bovine leukosis?

BLV is usually seen in animals 18 months and older. The disease evolves slowly, taking several months or years to develop.

There are no clinical signs during the initial infection, however, adult animals may exhibit any of the following symptoms:

• congestive heart failure;
• decreased milk production;
• paralysis due to neuronal involvement;
• progressive weight loss;
• recurring bloat; and
• weakness.

In most affected cattle, the enlargement of all lymph nodes is an outstanding symptom. Palpable lumps are found in the neck, in the front of the shoulder, and behind the udder.

Where is bovine leukosis found?

BLV occurs worldwide and has been observed in all cattle breeds. The infection is common in Canada (in the Atlantic provinces and Ontario) and in the U.S. As a result of mandatory eradication, the European Union countries now have a very low frequency of this disease and many have declared themselves free from infection.

How is bovine leukosis transmitted and spread?

BLV is transmitted from animal-to-animal (known as horizontal transmission), and less frequently from a mother to her offspring (vertical transmission).

Horizontal transmission requires the transfer of blood containing infected cells from one animal to another. Horizontal transmission often takes place via:

• shared needles and syringes;
• obstetrical sleeves;
• dehorning instruments;
• tattooing;
• ear tagging equipment; or
• surgical instruments.

Blood-sucking insects are also potential vectors for infection.

Vertical transmission accounts for 3 to 25 per cent of all infections. Placental transmission, after the third month of pregnancy, may occur at a relatively low rate. Semen, ova or embryos from infected cattle do not play a role in transmission.

The virus has also been found in whole milk and colostrum and may be a source of infection for calves. BLV persists for life in white blood cells (B-lymphocytes) of infected cattle.

How is bovine leukosis diagnosed?

The diagnosis of the disease is currently based on the detection of BLV antibodies in the blood and/or milk.

How is bovine leukosis treated?

There is no treatment or vaccine that will prevent infection. Pasteurizing or freezing colostrum or milk destroys BLV infectivity.

What is done to protect Canadian livestock from bovine leukosis?

As bovine leukosis is not a reportable disease under the Health of Animals Act, it is not subject to a regulatory program. Nonetheless, it is an economically important disease as many cattle-importing countries require bovine leukosis-free certification. Accordingly, the Canadian Food Inspection Agency (CFIA) has developed a voluntary Canada Health Accredited Herd Program to certify disease freedom in qualifying herds. This program meets international health standards and is delivered by private CFIA-accredited veterinarians and laboratories. It is based on test results, the removal of cattle infected with BLV, and the maintenance of a herd which only permits the entry of animals free of infection.

How do I get more information?

Contact your CFIA Area office:

Atlantic Area: 506-851-7651

Quebec Area: 514-283-8888

Ontario Area: 519-837-9400

Western Area: 403-292-4301

You can find your local CFIA District Office

• on the CFIA website at www.inspection.gc.ca
• by consulting the blue pages of your local phone directory.