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Animal Disease and Human Health Risk
Animal Disease and Human Health Risk
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Leukemia from Cows?
Many people think that cancer is only an adult disease. Nothing could be further from the
truth. Cancer is the second leading cause of death among U.S. children.115 Only accidents
claim more young lives. Leukemia, a cancer of the blood and blood forming tissues, is the
leading cause of childhood cancer deaths in our country, as stated in Figure 19: Cancer in
Children.116
Why is this of special concern in a chapter on diseases in animals? Because there is another
disease that is rampant in the American cattle population. This disease is bovine leukemia
virus (BLV). The possible connection of leukemia in children with this cattle disease is
explained in Figure 20: Potential Danger of the Bovine Leukemia Virus.117
Notice, as with BSE, there is a direct connection to cattle. Bovine leukemia virus (also
called the Bovine Leukosis Virus or BLV) refers, of course, to a form of leukemia occurring
in cattle. Note how prevalent this virus is in American dairy herds. Beef cattle usually
have a lower rate of infection. Nonetheless, at any time, roughly 20 percent of the U.S.
cattle population is infected.118 In addition to leukemia, this virus can cause bovine
lymphosarcoma, a cancer of the lymph tissues in cattle.
Note that the leukemia-infected cows themselves are not the only ones at risk. The virus
passes into the milk.119 This milk appears to have the potential to cause disease in
animals of other species who drink the infected beverage. BLV-contaminated milk that is
unpasteurized, when fed to sheep and chimpanzees, has been linked to serious diseases, as
shown in Figure 21: BLV Induces Tumors.120, 121
Still other species have been shown to be susceptible to BLV: white tail deer, pig, the
domestic rabbit, and cat.122 Ferrer and associates cited evidence years ago that in the
laboratory, human cells also become infected with the bovine leukemia virus.123
Pasteurization kills the virus,124, 125 but we have already seen that milk can become tainted
due to contamination after the pasteurization process or because of mechanical problems
with pasteurization equipment. Outbreaks of human infections from pasteurized milk due
to germs like E. Coli, salmonella, and Yersinia all provide examples of pasteurization's
shortcomings. In short, although pasteurization is a useful procedure that has increased
milk safety, it by no means sterilizes dairy products. Even after pasteurization, milk is
actually teeming with viruses and bacteria. Chapter 11 entitled "Milk, Friend or Foe?" has
more information on this subject.
Ultimately we ask ourselves, is BLV a threat to human health? The answer so far is that we
do not know. Although a single study showed more cases of human leukemias in areas that had
more cattle,126 other studies reviewed by Dr. Reginald Johnson of the U.S. Animal and Plant
Health Inspection Service found no relationship between BLV and human disease. It must be
pointed out, however, that bovine leukemia virus is very similar to the human T-cell
leukemia virus Type I (HTLV-1).127 Both are in the family of retroviruses that also
include HIV. The ability of this family of viruses to infect cells and then cause
disease years later is of particular concern. Consequently, the propensity for human
risk seems to be present although I am currently unaware of any definite human threat.
In short, BLV may or may not be causing human health problems. However, the BSE story
provides an eloquent example of how an infectious disease may appear at first to present
no human risk only to turn out later to be a serious threat. The fact that BSE and BLV
can both infect a wide variety of species is worthy of a final note. It seems prudent to
avoid any germ that can cross species barriers and cause life-threatening illnesses in
unrelated creatures.
References
115 Kochanek KD, Hudson BL. . Advance Report of Final Mortality Statistics, 1992. Monthly Vital
Statistics Report. Centers for Disease Control and Prevention. 1995;43(6) supplement: page 23.
116 Leukemia Society of America. Facts About Leukemia, Lymphoma, Multiple Myeloma, and Hodgkin's
Disease. New York, NY; 1995 p. 4.
117 USDA:APHIS (Animal and Plant Health Inspection Service). DxMonitor: Animal Health Report.
Winter 1995. Fort Collins, Colorado. P. 6-7. (Note: Florida in the 3rd quarter of 1995 had 31
of 42 cattle tested positive for a rate of approx. 74%).
118 USDA:APHIS (Animal and Plant Health Inspection Service). DxMonitor: Animal Health Report.
Winter 1995. Fort Collins, Colorado. P. 6-7.
119 Johnson R, Kaneene JB. Bovine Leukemia Virus. Part III. Zoonotic Potential, Molecular
Epidemiology, and an Animal Model. Compendium on Continuing Education for the Practicing
Veterinarian 1991;13(10):1631-1637.
120 Baumgartener L, Olson C, Onuma M. Effect of pasteurization and heat treatment on bovine
leukemia virus. J Am Vet Med Assoc 1976 Dec 1;169(11):1189-1191.
121 McClure HM, Keeling ME, et al. Erythroleukemia in two infant chimpanzees fed milk from cows
naturally infected with the bovine C-type virus. Cancer Res 1974 Oct;34(10):2745-2757.
122 Baumgartener LE. Bovine Leukemia Virus Transmission Studies. Diss Abstr Int (Sci) 1982;42
(11):4319-B.
123 Ferrer JF, Kenyon SJ, Gupta P. Milk of dairy cows frequently contains a leukemogenic virus.
Science 1981 Aug 28;213(4511):1014-1016.
124 Rubino MJ, Donham KJ. Inactivation of bovine leukemia virus-infected lymphocytes in milk.
Am J Vet Res 1984 Aug;45(8):1553-1556.
125 Baumgartener LE. Bovine Leukemia Virus Transmission Studies. Diss Abstr Int (Sci) 1982;42
(11):4319-B.
126 Donham KJ, Berg JW, Sawin RS. Epidemiologic relationships of the bovine population and human
leukemia in Iowa. Am J Epidemiol 1980 Jul;112(1):80-92.
127 Johnson R, Kaneene JB. 1991. Bovine Leukemia Virus. Part III. Zoonotic Potential, Molecular
Epidemiology, and an Animal Model. Compendium on Continuing Education for the Practicing
Veterinarian 13(10): 1631-1637.
Notice of Credit
The article above is compliments of the Uchee Pines Institute, Seale, Alabama, a teaching and
treatment facility devoted to natural remedies. For mor information, call 334-855-4781,e-mail:
ucheepine@csi.com, or visit their Website:
http://www.ucheepines.org.
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