Bovine Leukosis Virus (BLV)
in U.S. Beef Cattle

Bovine leukosis virus (BLV) is a retrovirus infection of
dairy and beef cattle. In less than 5 percent of infected
cattle, BLV causes malignant lymphoma which leads to
illness and death loss that may be economically
significant.

Signs of malignant lymphoma may include weight loss,
decreased milk production, enlarged lymph nodes, loss
of appetite, rear-limb weakness or paralysis, fever,
protruding eyeballs, gastrointestinal obstruction, heart
failure, and abnormal blood lymphocyte count. Bovine
malignant lymphoma (BML) is always fatal because
there are no economical and effective treatments. Other
economic losses associated with BLV infection are due
to restrictions on trade of infected animals and
germplasm.

There is no evidence that BLV is transmissible to
humans, and no human disease has ever been attributed
to BLV.

A national study of BLV in Canada in 1980 showed that
40 percent of its dairy herds and 11 percent of its beef
herds were infected. The national seroprevalence (a
measurement of the magnitude of BLV infection) in
dairy cattle was much higher than it was in beef cattle
(9.3 percent versus 0.5 percent). The Canadian Health
Accredited Herd (CHAH) program was established to
certify herds to be free of several diseases, including
BLV. BLV control programs have been established in
member countries of the European Economic
Community (EEC) since the 1980’s. Eradication
programs for dairy and beef cattle have been initiated in
Sweden, and seroprevalence studies of BLV are
underway in Norway, Latvia, and Poland. BLV
infection has been reported by many other countries, but
valid national estimates of seroprevalence are rare.
' AGID: Leukassay B, Pitman-Moore, Washington Crossing, NJ.
BLV ELISA Test: IDEXX Laboratories, Westbrook, ME.

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The USDA’s National Animal Health Monitoring
System (NAHMS) collaborates with others in the
livestock industry to provide information on national
animal health and related issues. NAHMS assessed
BLV seroprevalence in U.S. dairy operations in 1996 as
part of the Dairy ‘96 Study. Study findings showed that
89 percent of all U.S. dairy operations and 43.5 percent
of all U.S. dairy cattle were seropositive for BLV using
the agar gel immunodiffusion (AGID) test'. At least 25
percent of individual dairy cows were positive on 75
percent of the positive operations.

During the Beef ‘97 Study, NAHMS assessed BLV
seroprevalence in U.S. beef cow-calf operations. This
study included 2,713 operations from 23 of the leading
cow-calf states.” Blood samples were collected from
beef cows on 403 of those operations and sent to the
National Veterinary Services Laboratories in Ames
Towa to test for evidence of BLV infection. The AGID
test was used to test samples from 78.2 percent of the
cows’ sera on 76.5 percent of the operations that
participated in the biological sampling phase. During
the study, the AGID test was removed from commercial
production, and the remaining samples were tested with
the enzyme-linked immunosorbent assay (ELISA).
Studies have shown that the agreement between the
AGID test and the ELISA test is excellent.

Unlike the Dairy °96 Study, the number of herds
sampled in the Beef ‘97 Study were insufficient to
provide national estimates of BLV infection, however
the Beef ’97 Study results are valuable to researchers
and others. Thirty-eight percent of all beef operations
and 10.3 percent of all beef cows tested during the Beef
°97 Study were seropositive for BLV (Figure 1 on the
next page). Larger percentages of positive operations
and individual cows were found in the Southcentral and
Southeast regions (Figure 2). The lowest percentages of
positive operations and individual cows were in the
Wester region.

Alabama, Arkansas, California, Colorado, Florida, Georgia, Illinois, Iowa, Kansas, Kentucky, Mississippi, Missouri, Montana,
Nebraska, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Tennessee, Texas, Wyoming, and Virginia.


Figure 1

BLV Infection In Beef Cattle
Operation & Individual-cow Prevalence

50

Figure 2

BLV Infection In Beef Cattle
Prevalence By Geographic Region
75

40 fo

Percent Positive

Operation Individual Cow
Operation Level Versus Individual-cow Level
n= 403 operations, n= 10,994 cows. 6850

Viewed by herd size, the operation prevalence was
highest in herds of 1 to 49 cows (42.1 percent).
Likewise, the individual-cow prevalence was highest in
herds of 1 to 49 cows (17.6 percent). The operation
prevalence and individual-cow prevalence were lowest
in herds of 100 or more cows (Figure 3).

Less than 25 percent of the cows were positive on 56.4
percent of the positive operations (Figure 4). More than
75 percent of the cows were positive on 12.2 percent of
the operations.

NAHMS national estimates showed a high
seroprevalence and broad geographic distribution of
BLV infection in U.S. dairy herds. Though similar
national estimates for U.S. beef operations were not
determined, prevalence estimates for beef operations
that were sampled during the Beef ’97 Study indicated
lower prevalence in beef operations than dairy
operations. Regional prevalences in beef operations
varied from 13 to 51 percent, indicating the infection
occurs at varying levels in some regions of the U.S.

The high individual-cow prevalence on positive dairy
operations indicates that culling alone will not be a
cost-effective method for reducing BLV prevalence on
those operations. Regarding beef operations, control
strategies may vary, depending on the number of
infected animals. Culling alone may be effective in
some operations. In addition, implementation of a
program to reduce transmission may be necessary for
other operations.

The Beef ’97 Study provided estimates of BLV
infection on U.S. beef cattle operations that can be used
to: 1) assist herd control programs through education of
veterinarians, animal health officials, and producers,
and 2) provide baselines from which to monitor
progress. It is difficult to compare results of these
studies with information from other countries because
most countries, with the exception of member-countries

Region
BH Western
Wl Northcentral
50 “| =  southcentrat
E3 southeast

25

Operation Individual Cow
Operation Level Versus Individual-cow Level #3851

Figure 3

BLV Infection in Beef Cattle
Prevalence by Herd Size

Herd Size

“oy B1-49
8 50-99
3 o|| |. 100 or More
be
Eo»
é
10
° : :
Operation Individual-cow
Operation Level Versus Individual-cow Level #3853,
Figure 4

Percent of BLV-positive Beef Cows
on BLV-positive Operations

60
5 50
iC]
2 20 ||
E ol
8
8 401]
é

0

1-24 25-49 50-74 75-100
Percent Cows Positive

11= 156 positive operations. n= 403 ol operations. 0055

of the EEC (where control efforts have been underway
for many years) and Canada, have not published results
from prevalence surveys.

For more information, contact:

Centers for Epidemiology and Animal Health, USDA:APHIS:VS,
attn. NAHMS, 2150 Centre Ave., Bldg. B, MS 2E7, Fort Collins,
CO 80526-8117, (970) 494-7000, E-mai
http://www.aphis.usda.gow/vs/ceah/cahm

NAHMS collaborators included the National Agricultural
Statistics Service (USDA), National Veterinary Services
Laboratories (NVSL), and State and Federal Veterinary Medical
Officers and Animal Health Technicians. NAHMS Info Sheet
reviewers included staff from the Agricultural Research Service,
private industry, Washington State University, Virginia Tech
University, and Kansas State University. 1N299.299

: NAHMSweb@aphis.usda.gov,