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Bovine Leukemia Virus

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Bovine leukemia virus causes a blood-borne infection in cattle. The virus survives in

the white blood cells (lymphocytes), resulting in chronic infection. Most cattle never

show symptoms, but a small percentage develop malignant lymphoma and

lymphosarcoma.
The virus is endemic in the United States and affects cattle in many other parts of

the world as well.

While common and often benign, having this virus in a herd is costly. Economic

losses include reduced milk production, premature culling, cattle deaths (from

lymphosarcoma), increased replacement and veterinary costs, and trade restrictions

on infected animals and germplasm.

What To Look For

Most infected animals (about two-thirds) show no outward signs of disease,

especially younger animals (under 2 years). Less than 5 percent develop

lymphosarcoma (most common in 4- to 8-year-old animals). The remainder develop

persistent lymphocytosis.

When animals do show signs, they vary and may include:

Swollen lymph nodes

Labored breathing (dyspnea)

Bloating

Jugular vein distention

Increased heart rate (tachycardia)

Brisket edema

Weight loss

Decreased milk production

Fever

Loss of appetite

Infertility

Rear limb weakness or paralysis

Protruding eyeball (exophthalmia)

Gastrointestinal obstructions and/or ulcers with digested blood (melena)

Increased blood lymphocyte counts

How To Prevent This Disease
Bovine leukemia virus spreads when uninfected animals come into contact with

blood, saliva, semen, or milk from infected animals. This usually happens during

routine farm practices (for example, tattooing, dehorning, rectal palpation,

injections, blood collection).

The virus can also spread from an infected female to her fetus or immediately after

birth when the newborn calf ingests infected colostrum. Insect vectors such as

Tabanid spp. and other large biting flies may also transmit the virus.

Here's what you can do:

Use cautery or other bloodless methods of dehorning.

Clean and disinfect all equipment between animals for procedures, such as

castration, tattooing, and ear tagging.

Never reuse needles between animals for blood collection or injections.

Keep handling facilities clean.

Control biting flies to lower your animals' risk of exposure.

Test animals regularly for the virus to detect infections early and eliminate

them from the herd.

There's no vaccine for bovine leukemia virus. Preventing its spread is the best way

to protect your herd.

How It Is Treated

There's no treatment for bovine leukemia virus or for lymphosarcoma in cattle.

Only management practices can eliminate the virus from a herd. Options include:

1. Identify infected cattle and slaughter positive reactors.

2. Detect and isolate infected cattle, and then manage infected and non-infected

cattle in separate herds.

3. Test animals for the virus and take appropriate biosafety and management

measures to minimize exposure for non-infected animals.

Report Signs of Animal Disease
Producers or owners who suspect an animal disease should contact their

veterinarian to evaluate the animal or herd. Find an accredited veterinarian.

Animal health professionals (veterinarians; diagnostic laboratories; public health,

zoo, or wildlife personnel; and others) report diagnosed or suspected cases of

nationally listed reportable animal diseases to APHIS District Offices and to the State

animal health official as applicable under State reporting regulations. 

Controlling Bovine Leukemia Virus

Current Status

Bovine leukemia virus is a common disease in U.S. dairies. Its prevalence in beef

cattle is increasing. Previous national studies showed that 89 percent of U.S. dairy

herds and 38 percent of U.S. beef herds had infected animals.

Bovine Leukosis Virus on U.S. Dairy Operations, 2007 (36.76 KB) (APHIS

Veterinary Services, National Animal Health Monitoring System)

Bovine Leukosis Virus in U.S. Beef Cattle, 1999 (225.26 KB) (APHIS Veterinary

Services, National Animal Health Monitoring System)

Information for Veterinarians

Overview of Bovine Leukosis (Merck Manual)

Preventive and Therapeutic Strategies for Bovine Leukemia Virus: Lessons for

HTLV (Viruses, a journal of virology)

Invited review: Bovine leukemia virus—Transmission, control, and eradication

(ScienceDirect)

Testing

Virus-specific antibodies found in serum or milk are a good indicator of exposure and

a practical method for disease screening. Agar gel immunodiffusion (AGID), enzymelinked immunosorbent assay (ELISA), and polymerase chain reaction (PCR) tests are

all used to identify bovine leukemia virus-positive animals.