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MAD COW DISEASE: A SOBERING "WAKE UP CALL"?
Copyright 1996 by David J. DeRose, MD, MPH
"Mad Cow Disease" grabbed headlines in late March 1996 when a group of
prestigious British Scientists were constrained to admit that the fatal disease could
possibly be transmitted to humans. The news brought the British meat industry to a virtual
standstill. English folk avoided the meat markets. The European Union and a cascade of
other countries banned British beef.
Referred to as Bovine Spongiform Encephalopathy (BSE) by the medical community, the
illness is aptly named. The designation makes it clear that we are talking about a brain
disease (encephalopathy) that affects cows (bovine). Furthermore, the disease riddles the
afflicted cow's brain with tiny holes--causing it to look like a sponge under a microscope
(thus rendering the brain "spongiform"). The lay term, "mad cow
disease," in addition to being much easier to pronounce, also conveys the fact that
infected cows may develop mental deterioration and behavioral abnormalities.
First diagnosed in Britain in 1986, BSE has powerful emotional appeal. It is one of a
group of fatal brain diseases that can be transmitted from one living creature to another.
These diseases are technically called "transmissible encephalopathies." Many
British consumers had apparently comforted themselves for years with the thought that it
was unlikely for such a disease to spread from cows to humans. However, even before March
1996, I would guess that scientists who were aware of this fatal cattle disease would--if
honest--have to admit to some level of discomfort. After all, transmissible
encephalopathies affect many other creatures besides cattle. Some 16 or18 animal species
have been documented to come down with diseases that resemble BSE. Many or all of those
species can apparently get a BSE-like disease from eating infected cattle meat.
Furthermore, cattle themselves likely contracted the disease from a different species.
Most researchers believe that BSE was introduced into British cattle herds by feeding them
dead sheep carcasses which were infected with a similar illness called
"scrapie." (The sheep disease gets its name from the fact that afflicted sheep
can become mentally unstable and literally "scrape" the wool off their hide.)
HUMANS CAN GET TRANSMISSIBLE ENCEPHALOPATHIES
However, it is not only animals that can contract transmissible encephalopathies. Humans
can also get them. A disease called Creutzfeldt-Jakob disease (CJD) can be thought of as a
type of fast acting Alzheimer's disease. This is an extremely rare illness that has
typically occurred in older individuals. I have personally only seen one patient with this
rare and fatal disease.
We know from cannibalistic tribes in New Guinea, that a disease like CJD is transmissible
to humans. There, at one time, the dead were honored through ritual cannibalistic rites.
Children typically ate the brains of their deceased parents during these rituals. Many of
them did get a disease called "kuru" which is a transmissible spongiform
encephalopathy similar (if not the same as) CJD. The disease sometimes took up to 30 years
to develop. Young children who engaged in these cannibalistic practices tended to develop
the illness sooner than their older siblings or peers who also consumed infected brains.
Many scientists had speculated that if sheep could transmit the disease to beef, beef
could transmit the disease to humans. In fact even in the United States, a country which
claims to have no evidence of BSE, there have been reports that are less than comforting.
For example, an outbreak of a related illness, Transmissible Mink Encephalopathy occurred
on a Wisconsin mink farm. It was discovered that the mink illness was likely related to
that farmer's practice of feeding them local "downer" dairy cows. This is a
designation for cows that either are so ill that they fall down and can not get up, or
actually are found dead on the farm. Deemed unfit for human consumption, such cows have
been used for animal feed among other things. In this case, the carcasses found their way
into the minks' diets.
The mink outbreak provided another example of probable BSE infecting other species. (The
link could not be made definitely since the "downer cow or cows" that were fed
to the mink were not autopsied.) It also raised another concern: countries like the US who
think they have nothing to worry about, may in fact have diseased animals in their herds.
Despite assurances from the USDA that BSE has not crossed the Atlantic, the mink story
leaves us with an uncomfortable feeling. However, there is even more disturbing news.
Laboratory research has demonstrated that different strains of prions do exist. For
example, a British researcher found that when he injected the prions from an infected
group of goats into mice, those mice developed an encephalopathy (brain disease)
characterized by drowsiness. The prions from a different group of infected goats also
caused brain disease when injected into mice; however, instead of becoming lethargic, the
diseased mice turned hyperactive! The message was clear: there were apparently at least
two different strains of scrapie-like illness in goats. When transmitted to another
species (in this case the mice) the infected rodents came down with one or the other of
these two very different looking diseases.
Such research has raised an important question. If scrapie in goats could give rise to
different appearing diseases in mice, could sheep scrapie result in more than one type of
cow disease? There is some suggestion that this could be the case. There may well be more
than one strain or type of BSE. The different types may cause different looking diseases.
Some who have been studying links between cattle and mink disease in the US, have raised
the concern that BSE is present in America, but "looks different" than the
British variant due to a different BSE strain. Specifically, the BSE in the US may be one
cause of "downer cow" disease rather than its "mad cow" cousin in
England.
FINALLY TAKING NOTICE
It was Creutzfeldt-Jakob statistics that really got the medical community's attention in
March 1996. By that time some eight young Britons had succumbed to this devastating
illness. The unusual occurrence of the disease in young people combined with a different
pattern to the sponge-like brain destruction, prompted leading British scientists to raise
the concern that BSE may be the source of a new variant of CJD. Further thickening the
plot was the occurrence of a worrisome cluster of CJD in British dairy farmers.
The biggest concern, of course, is that we are just glimpsing the tip of that proverbial
iceberg. One prominent researcher is putting estimates of BSE-related CJD well into the
thousands. And the problem does not appear to be confined to Britain. There are worrisome
reports now from France and Italy. Still others are raising concerns that some cases of
"Alzheimer's" may actually be spongiform encephalopathy. Granted, all of these
conjectures may not prove true; but what if just some of them are? Even if only in part?
PRIONS: FRIGHTENING CARRIERS OF DISEASE
Adding to the fear of this relatively newly appreciated disease is the nature of the BSE
infectious agent. Many animal borne diseases are caused by bacteria or viruses. Risk from
these illnesses can often be decreased or eliminated by a combination of careful washing,
refrigeration and thorough cooking. Bovine spongiform encephalopathy, however, appears to
be caused by an unusual infectious agent known as a "prion" (pronounced
"pree-on"). Prions are truly very unusual infectious agents. They have no
genetic material and consist entirely of protein. Research suggests that these prion
proteins are similar in structure to proteins that occur naturally in the brains of humans
and other animals. The prions differ from those similar normal proteins, however, in their
three dimensional shape. Prions seem to cause disease by coming into contact with those
normal proteins and then stimulating them to change their shape to mimic the prion
protein. This change in shape appears to set up a chain reaction. Normal proteins change
their shape to look like the prion proteins and then later influence neighboring proteins
to do the same. The end result is a progressively devastating and ultimately fatal
disease. No treatment has yet been discovered.
Making the picture even bleaker is the resiliency of prions. They are not destroyed by the
usual means used to kill infectious agents. They are resistant even to boiling at
temperatures as high as 250 degrees Celsius (well over 400 degrees Fahrenheit). They are
also resistant to ionizing radiation.
Prion related diseases are also extremely difficult to diagnose. There is no way to do a
blood test for BSE and an infected animal does not mount any immune response to the
infection. Tell-tale signs of diseases like BSE are usually only possible to diagnose at
autopsy. However, not all infected animals necessarily have the characteristic sponge-like
brain changes. Of particular concern, animals who carry the disease and have not yet
developed signs of BSE, may not show the characteristic brain involvement.
WHAT ANIMAL PRODUCTS ARE FREE OF PRIONS?
Of even more concern is the fact that we do not know which tissues could carry the
infection. Most of the focus of late has been on beef. This is warranted. Although organ
tissue carries the greatest risk, animal studies do suggest that meat itself can transmit
prion-related diseases. However, we cannot exclude the possibility that milk could also
carry disease-inducing prions. Many may recall how some years ago assurances were given
that a mother could not pass HIV to her child by nursing. Of course, we now know that HIV
can be transmitted in breast milk. Granted, prion diseases are vastly different than HIV.
The risk from milk (if it does exist) does appear to be much smaller than from eating beef
or cattle organ tissues. Nonetheless, a British BSE expert has pointed out that there has
been at least one human case that suggests passage of prions in milk. This was the case of
a woman dying with CJD who demonstrated the infectious agent in her colostrum (the type of
breast milk made in the initial days following delivery).
Eating the flesh of other animals (besides cows) or drinking their milk may not be safe
either. These other animals may also be affected with a prion-related diseases. As we have
already mentioned, sheep as well as goats can become infected with such illnesses. Even if
some of these illnesses do not seem to be easily transmitted to humans (because of what is
often called, "the species barrier"), the possibility exists that different
strains of prions could present more danger.
OTHER CONSIDERATIONS
There is one other very important aspect that needs to be reemphasized. These
transmissible spongiform encephalopathies have extremely long incubation periods. (This is
the technical term for how long it takes for a person with the infection to actually show
signs of the disease) As already mentioned, in humans, there is evidence that kuru can
take up to 30 years to manifest itself. This is likely to be the same with CJD. With BSE,
it may take up to 6-8 years or more before infected cows show signs of the disease. The
important implication is that thousands of animals and humans may now be infected yet not
develop symptoms for many years.
The current British proposal to slaughter all older cows may not go far enough. If younger
cows are infected they may not yet show any signs of the disease. However, an infected cow
can theoretically transmit the illness whether or not it has yet developed symptomatic
disease. The widely publicized 1988 ban on feeding dead sheep parts to British cattle did
not stop the epidemic. When the statistics were reviewed in a 1995 report, over half of
all the British cattle that had developed BSE were born after the ban was implemented. The
important message is that young cows may be infected, and may be able to transmit disease
to humans.
CONCLUSIONS
The Consumers' Association , an independent British "watchdog group", has been
quoted as saying that the only way to avoid BSE risk would be to stop eating beef all
together. Others are saying even more. Some are suggesting that the time has come to
recognize that disease in animals has become so rampant that we all need to seriously
consider becoming vegetarians. They point out that BSE is just one of many fatal diseases
linked to animals. Literally hundreds of deaths have been documented in the US alone from
a host of animal related infections. Some of the most significant causative agents may not
yet be household words, however most will recognize at least one of them: salmonella,
listeria, campylobacter, and yersinia. Of course, we can't forget that the risk of dying
prematurely from the Western World's two leading killers, cancer and heart disease,
generally rises with increasing consumption of animal products.
If there is even a small chance of getting a severe fatal disease, some are suggesting it
would be prudent to avoid all animal products. But maybe a few other questions are more
important. What is the next transmissible disease in animals that will be recognized? Do I
want to wait for tragedy to strike me or someone close to me--or have I already had
warning enough?
APPENDIX: IS IT ALREADY TOO LATE?
If you have been eating beef and using other animal products for years is it already too
late? The answer is clearly, "no." In the case of human prion related diseases,
there is evidence that the total amount of prion exposure affects the incubation period of
the disease. In other words, someone who eats a large amount of prion containing foods may
develop the disease in 10 years or less, while someone with moderate, yet significantly
less, exposure may develop the condition in 15-20 years. Another with still smaller
exposure may not come down with the illness for 30 or more years.
Thus, even if someone was doomed to come down with a condition like CJD (because of
previous exposure to prions), it may be possible to delay the onset of the disease
significantly. And don't forget: a diet that moves away from animal products can also
dramatically help you decrease your risk of other diseases like heart disease and cancer.
FURTHER INFORMATION
Those interested in additional information on BSE and/or other animal related diseases are
encouraged to ask to be placed on the mailing list for prepublication information on Dr.
Neil Nedley's book when it becomes available. In addition to the written text, an
accompanying CD-ROM with color visuals suitable for public presentations will be
available. Send e-mail to "docderose@aol.com" with the request "Nedley
list" (leave off the quotes, of course.) You will receive further information when it
becomes available.
SELECTED REFERENCES:
Almond JW, Brown P, Gore SM, Hofman A, Wientjens DPWM, Ridley RM, et al. Will bovine
spongiform encephalopathy transmit to humans? . British Medical Journal 1995;311:1415-21
(25 November)
Brown, P. Bovine spongiform encephalopathy and Creutzfeldt-Jakob disease: The link is
unproved, but no better explanation is presently forthcoming. British Medical Journal, 30
March 1996
Dealler SF, Lacey RW Transmissible spongiform encephalopathies: the threat of BSE to man.
Food Microbiology 1990;7: 253-79.
Dealler, S & Kent, J. BSE: an update on the statistical evidence; British Food Journal
1995, volume 97, p3-18;
Gore SM. More than happenstance: Creutzfeldt-Jakob disease in farmers and young adults.
British Medical Journal 1995;311:1416-8.
Gore, SM Bovine Creutzfeldt-Jakob disease? Failures of epidemiology must be remedied.
British Medical Journal, 30 March 1996
Gruzen, T; U.S. Never Banned Suspect Feed Fda, Keeping Watch On British Beef Crisis, Says
Safeguards Exist; Chicago Tribune, Thursday, March 28, 1996
Hoinville LJ, Wilesmith JW, Richards MS. An investigation of risk factors for cases of
bovine spongiform encephalopathy born after the introduction of the "feed ban."
Vet Rec 1995;136:312-8.
Lacey RW, Bovine spongiform encephalopathy is being maintained by vertical and horizontal
transmission, British Medical Journal 20 January 1996;312:180-1.
Lacey RW. Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. British Medical
Journal 1996;312:180-1. (20 January)
Patterson, WJ & Dealler, S. Bovine spongiform encephalopathy and public health. J.
Public Health Medicine. Volume 17 number 3, 1995, pages 261-268.
Prusiner SB, Molecular Biology Of Prion Diseases. Science (Magazine) Vol. 252, pages
1515-1522; June 14, 1991.
Prusiner SB, The Prion Diseases. Scientific American. January 1995 Volume 272 Number 1
Pages 48-57.
Wells GAH, Wilesmith JW. The neuropathology and epidemiology of bovine spongiform
encephalopathy. Brain Pathol 1995;5:91-103.
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This article is reproduced from The WellnessWise Electronic Journal, copyright David J.
DeRose, MD, MPH.
Back issues of WEJ are available at several sites in cyberspace. Some of the
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Send all correspondence to:
David J. DeRose, MD, MPH
E-mail addresses: docderose@aol.com or 74532.622@compuserve.com
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