Have Millions of Americans Been Infected with a Cow Cancer Virus?
by Michael Greger, M.D.
January 9, 2004
Lost in the recent media flurry over Mad Cow disease, a provocative
study was released in the latest issue of AIDS Research and Human
Retroviruses. Researchers at the University of California,
Berkeley found that a significant proportion of the American public
may be harboring antibodies to Bovine Leukemia Virus, which they may
have been exposed to through the consumption of beef or dairy
Bovine Leukemia Virus (BLV) is a retrovirus that causes leukemia in
cattle. BLV infected cells (lymphocyets) circulate through the blood
of cattle and are present in both beef and milk. As soon as BLV
was isolated in 1969 there were efforts to determine whether humans
were infected with the virus. Using the best tests available at the
time, researchers weren't able to detect antibodies to the virus in
the bloodstream of any human tested and so the USDA had concluded
that, "BLV is not transmissible to humans."
Compared to modern testing techniques, though, the tests they were
using in the 1970's were extremely insensitive. Realizing that back
then, researchers were even missing up to 70% of the positive bovine
cases, Dr. Gertrude Case Buehring anf collegues at the University
of California School of Public Health in Berkeley wondered whether
the newer, more advanced testing methods would be able to detect
antibodies against BLV in human blood after all. So she took blood
samples from 257 people, mostly women, and tested them. Late last
month her results were published.
The study was designed to see if any humans at all had antibodies to
BLV. Dr. Buehring's group found antibodies reactive specifically
against BLV in 191 out of the 257 people studied. An amazing 74% of
the human subjects tested positive. Extrapolating this finding to the
general population, hundreds of millions of Americans may have been
similarly exposed to Bovine Leukemia Virus.
How did these people get exposed to this cattle virus? Less than 10%
had any direct contact with live bovines. Therefore, the most likely
explanation was due to their direct contact with dead ones (through
beef) or through live cow secretions (dairy products).
What exactly does it mean that people have antibodies against the
virus? Typically, the presence of antibodies to a particular virus
indicates either past or present infection with that virus. Dr.
Buehring concedes, though, that the presence of antibodies may just
be an immune response to consuming dead virus, killed by the
sufficient cooking or pasteurization of infected meat or milk . At
this point we don't have enough data to distinguish between the two
possibilities--active human infection from Bovine Leukemia Virus in
unpasteurized milk or undercooked meat, or merely exposure to killed
If people can acquire active BLV infections, what consequences might
that have for their health? Public health advocates often point to a
study done 30 years ago in which 6 baby chimpanzees were fed
unpasteurized milk from BLV infected cows. The two infant chimps fed
the most infected milk were dead within a year of leukemia.
Of course just because other primates become infected and die of
leukemia drinking infected milk, this doesn't mean that humans will.
Unfortunately, studies on human cell lines shows that indeed human
cells can also become infected with the BLV virus. This still
doesn't necessarily mean that BLV can cause human disease, though.
Researchers needed to start studying human populations to see if they
could detect any association between BLV and human cancer rates.
Researchers found a disturbing trend. They found that geographically,
the areas of highest cattle BLV infection did indeed seem to have
significantly higher human leukemia rates. For example, in a study in
Iowa, the counties reporting the highest rates of cattle BLV
infection seemed to also have the highest rates of human acute
lymphoid leukemia (ALL), which typically strikes children. Other
studies have found that milk consumption, for example, was associated
with the development of malignant lymphomas.
BLV currently infects the majority of dairy and beef herds in the
United States and Canada. In fact, an estimated 89% of the dairy
herds in the U.S. harbor infected animals. Europe, on the other
hand, has very few infected animals. This may be, in part,
because some of the ways in which young calves are treated in this
country have been deemed too cruel and banned in Europe.
Instruments used in these procedures in the U.S.--ear taggers, nose
tongs, hoof knives, tattoo pliers, the needles on hormone implant
guns--may be inadequately sterilized and therefore may spread the
Take, for example, dehorning. The saws and gougers used in dehorning
young calves cause so much bleeding and are so hard to clean that
they are particularly likely to drive potentially infected blood into
the next animal in line. Dehorning is done in part to minimize
injuries to handlers and to reduce bruising during transport. To
minimize the risk of transmission of blood-borne pathogens like BLV,
the industry is moving away from gougers and more towards red-hot
electric irons or caustic paste to burn off the horn button.
A modern Dairy Management textbook explains the use of the electric
iron: "lie the calf on its side and put your knee on the neck... The
dehorner has to be left on the button for approximately 5-20 seconds.
The time will seem longer, because of the combined unpleasantness of
burning hair and a struggling calf...dehorning may be complete...
when you hear a squeaking sound as the dehorner is twisted. It is the
sound of the dehorner tip rubbing against the bone of the skull."
Surgical castration--in which the lower third of the calf's scrotum
is cut off and the testicles are grabbed and literally just ripped
out--is another opportunity for blood-stained instruments to spread
infection. Both dehorning and castration are done in calves just 2-3
weeks old without any anesthetic. The USDA notes that although
"Animal welfarists criticize the failure to administer anesthetics...
not using anesthetics for those relatively simple procedures greatly
reduces the complications caused by anesthetics...."
Other examples of practices that can spread BLV infection--done to
modify the animal to fit the system, rather than adapt the system to
accommodate the animal--are tail docking, which reduces the "chance
of the farmer getting swatted in the face," and "extra" teat
removal to "improve udder appearance."[19 ]
Tail docking is becoming more widely accepted by dairy farmers.
Although one dairy textbook notes that "Some people object to the
docking of tails for humane reasons. In fact, the practice of docking
tails is banned in Great Britain. Others see no difference between
docking cattle compared to docking the tails of pigs and sheep or the
dehorning of cattle."
Removing "extra" teats is another unnecessary procedure that can
expose calves to infection. Up to half of all female calves are born
with "extra" teats on their udders. Dairy practitioners are taught
that "Extra teats should be removed for cosmetic reasons... " The
Holstein Foundation explains "Extra teats on an udder are
unsightly..." The "extra" teats may also interfere with proper
placement of the milking machinery.
A Dairy textbook explains the procedure: "extra teats detract from an
udder's general appearance. Grasp the teat between your thumb and
forefinger. Even in small calves, the nerve supply to their teats are
well developed. Make sure the calf is well restrained before you
proceed. Pull the teat outwards and take a generous bite with the
scissors." Slicing these nipples off of young calves is also done
By continuing these unnecessary practices, we may be increase the
risk of spreading this diease throughout the U.S. cattle herd and by
extension, into the human population. The December study in AIDS
Research and Human Retroviruses concludes, "The long-held assumption
that BLV is not a public health hazard was based on the failure of
experiments in the 1970s to detect human antibodies to BLV. That
assumption is no longer tenable in view of our demonstration of
humans seropositive for BLV-reactive antibodies."
The preceding was excerpted from Dr. Greger's January 2004
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Michael Greger, M.D., has been the Chief BSE Investigator for Farm
Sanctuary since 1993 and the Mad Cow Coordinator for the Organic
Consumers Association since 2001. Dr. Greger has debated the National
Cattlemen's Beef Association before the FDA and was invited as an
expert witness at the infamous Oprah Winfrey "meat defamation" trial.
He has contributed to many books and articles on the subject,
continues to lecture extensively, and currently runs the Mad Cow
disease website http://www.organicconsumers.org/madcow.htm.
Greger is a graduate of the Cornell University School of Agriculture
and the Tufts University School of Medicine. He can be reached for
media inquiries at (206) 312-8640 or mhg1@...
(Full text of specific articles available by emailing
1 AIDS Research and Human Retroviruses 19(2003):1105.
2 Science 213(1981):1014.
4 Journal of Virology Methods 104(2002):33.
5 Cancer Research 34(1974):2745
6 Cancer Research 36(1976):4152.
7 American Journal of Epidemiology 112(1980):80.
8 British Journal of Cancer 61(1990):454.
9 Veterinary Research 25(1994):521.
10 Working with Dairy Cattle.
11 DairyBiz February 1999. http://www.moomilk.com/archive/a_health_29.htm
15 Practical Techniques for Dairy Farmers. 3rd Ed. University of
16 Practical Techniques for Dairy Farmers. 3rd Ed. University of
17 Arave, CW and JL Albright. "Animal Welfare Issues: Dairy." AWIC
Newsletter 9(1998):3-10. The Animal Welfare Information Center is
part of the USDA Agriculture Research Service.
18 Practical Techniques for Dairy Farmers. 3rd Ed. University of
19 Dairy Connection December 1999.
20 Practical Techniques for Dairy Farmers. 3rd Ed. University of
21 Management of Dairy Heifers.
22 Dairy Connection December 1999.
23 Practical Techniques for Dairy Farmers. 3rd Ed. University of
24 Working with Dairy Cattle.
25 AIDS Research and Human Retroviruses 19(2003):1105.
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