. RACHEL'S ENVIRONMENT & HEALTH WEEKLY #607 .
. ---July 16, 1998--- .
. HEADLINES: .
. MAD COW DISEASE, PART 2 .
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MAD COW DISEASE, PART 2
Mad cow disease appeared for the first time in Britain in 1985.
Since that time it has killed roughly 170,000 cows in Britain,
and it has spread to humans. In humans the disease is called
"new variant Creutzfeld-Jakob disease," or nvCJD for short. At
this point nvCJD has killed 24 people in Britain and one in
France. More human deaths are expected in Britain because
several million people ate diseased beef before the British
government (or the beef industry) acknowledged that mad cow
disease could infect people.
>From a U.S. perspective, the obvious question is, How can an
outbreak of mad cow disease be prevented here?
Mad cow disease is a member of a family of rare diseases called
transmissible spongiform encephalopathies, or TSEs. TSEs have
different names in different animals (for example, scrapie in
sheep, chronic wasting syndrome in deer and elk, and bovine
spongiform encephalopathy or BSE in cows). However all TSEs
share a few common features: they attack the central nervous
system, causing disintegration of the brain; they have a long
incubation period between the time when infection first occurs
and the appearance of symptoms; TSEs are always fatal; and they
are transmitted by the eating of animals or animal parts,
especially brains and spinal cords.
TSEs are now thought to be caused by a unique disease agent,
called a prion (pronounced PREE-on). A prion is simply a
particular kind of protein. All mammals have prions, and some
non-mammalian species have them as well. Prions are normal.
According to modern biology, a prion should not be able to
reproduce itself, and therefore should not be able to cause
disease, because prions contain no DNA. Without DNA,
reproduction should not be possible. However, it is now becoming
widely accepted that prions do reproduce themselves and do cause
disease. Somehow a normal prion goes bad --it gets folded into
an abnormal shape and in its abnormal shape it can destroy nerve
cells in the central nervous system. The abnormal prions also
cause other nearby prions to become folded into the same shape,
thus creating more abnormal prions by a domino effect. After a
long period of time (months or years, or even decades) the
symptoms of disease appear, followed a few weeks or months later
by death. Thus animals and humans can be carrying an infectious
prion disease for months or years without showing any symptoms.
The prion theory of disease is still not accepted by 100% of the
scientific community, but the inventor of the theory, Stanley B.
Prusiner of the University of California at San Francisco,
received the Nobel Prize for his work in 1997.
In this country, the government agency with primary
responsibility for preventing an outbreak of mad cow disease or
its human variant, nvCJD, is the U.S. Food and Drug
The FDA in 1997 issued a rule declaring it illegal for farmers to
feed animal protein from ruminants or mink to other ruminants --a
preventive step that had been taken by the British government in
1988. Ruminants are animals that chew their cuds, including
cattle, sheep, goats, deer and elk. Mink are included in the
FDA's ban because they can get a TSE similar to mad cow disease.
When cows, pigs, and chickens are slaughtered, much of the animal
cannot be used for food and is sent to a rendering plant to be
ground up, boiled down, dried to the consistency of brown sugar
and sold as feed for cows, pigs, chickens, and pets. It is this
rendered "animal protein" derived from ruminants (and mink) that
FDA has banned from feeding to ruminants.
The FDA's ruminant-to-ruminant ban still allows animal protein of
all kinds to be fed to pigs and chickens, and it allows animal
protein derived from pigs and chickens to be fed to ruminants.
The FDA ban also allows blood and gelatin derived from ruminants
to be fed to other ruminants. In the U.S., many newborn calves
are fed a high-protein diet consisting mainly of dried blood.
Blood cells carry prions just as nerve cells do.
A small group of scientists, led by Dr. Michael Hansen of
Consumers Union, has challenged the adequacy of FDA's
ruminant-to-ruminant rule. They argue that the FDA ban does
not go far enough, "does not adequately protect human health, and
is not scientifically defensible." Consumers Union is the
publisher of CONSUMER REPORTS magazine.
Scientists on both sides of the controversy agree that mad cow
disease probably developed in Britain in one of two ways.
Possibly cows ate parts of sheep that had been infected with the
TSE called scrapie, and the scrapie, once in cows, evolved into
mad cow disease. Or, alternatively, a prion spontaneously went
bad (via genetic mutation of the gene that produces normal
prions) in a cow, and that cow was fed to other cows, which were
fed to other cows until the disease was amplified into an
epidemic. In either case, it was cows (which are vegetarians by
nature) being forced to eat animals that created the problem.
FDA officials say they are confident that their
ruminant-to-ruminant ban has prevented, and will continue to
prevent, an epidemic of mad cow disease in this country because
(a) mad cow has never been observed in cows in the U.S., and (b)
Creutzfeld-Jakob (CJD) disease is not increasing in the U.S.
If mad cow were occurring in U.S. cows, some form of CJD should
be increasing, and it isn't, the FDA argues.
Michael Hansen of Consumers Union offers evidence that the
government may be wrong on both counts. Here are his arguments:
Mad cow may have already appeared in U.S. cows. Hansen offers
evidence from seven studies that some "downer" cows may have a
form of mad cow disease, though with symptoms somewhat different
from those in British cows. Downer cows are cows that cannot
stand up, cows that collapse, and cows that die mysteriously.
About 100,000 cows die each year in the U.S. with "downer"
symptoms, and most of them end up in rendering plants, turned
into animal feed.
In 1961, an outbreak of transmissible mink encephalopathy (TME)
--a brain-destroying TSE of mink --occurred on six mink farms in
Wisconsin. Because all the farms used the same ready-mix feed
which came from the same feed plant, investigators assumed that
the feed was the source of the infectious agent. Two years
later, in 1963, an outbreak of TME occurred on two more Wisconsin
mink farms. Based on the 1961 outbreak, scientists suspected
feed and they examined the two farms' feed records carefully.
They learned that "downer" cows from farm A had been fed to mink
on Farm A and Farm B. The researchers wrote, "Since mink on both
farms developed the disease almost simultaneously, we believe
this feed component has to be incriminated."
In 1985 an outbreak of TME occurred on a mink ranch in
Stetsonville, Wisconsin. Dr. Richard Marsh of the University of
Wisconsin investigated and found that the mink had been fed 95%
downer cows and 5% horse meat. When brains from infected
mink were injected into two calves, within 19 months both calves
had a bovine TSE but they did NOT exhibit the symptoms of
Britain's mad cows. The Stetsonville cows simply became
lethargic and then fell over. In other words, they exhibited
typical "downer cow" symptoms. When brains from these cows were
injected into mink, the mink got TME, confirming the kind of
disease that had killed the cows. Marsh and his colleagues
concluded, "These results suggest the presence of a previously
unrecognized scrapie-like infection in cattle in the United
Marsh's cattle inoculation experiments have been repeated and,
again, mink TME was transmitted to cows and back to mink and the
cows exhibited "downer" symptoms, nothing like British mad cow
disease. Furthermore, in 1979 U.S. Department of Agriculture
researchers in Mission, Texas, inoculated 10 cows with sheep
scrapie. Three of the 10 cows developed neurological symptoms,
but they were more like "downer cow" syndrome than British mad
cow disease: "progressive difficulty in rising, a stiff-legged
gait, incoordination, abnormal tail position, disorientation, and
terminal recumbency [lying down]," according to Dr. Clarence
Gibbs, Acting Chief of the Laboratory of Central Nervous System
Studies at the National Institutes of Health. Ten years
later, when a test for mad cow disease became available, Dr.
Gibbs confirmed a bovine TSE disease in the three cows, whose
brains had been preserved. Dr. Gibbs concluded,
"Susceptibility of cattle to scrapie further suggests the
possibility that sporadic cases of BSE [mad cow disease] may have
occurred in the United States under the clinical picture of the
downer cow syndrome...."
After Gibbs confirmed that the Mission, Texas cows had indeed
died of a TSE, the U.S. Department of Agriculture repeated the
experiments at Ames, Iowa under the direction of Randall
Cutlip. Dr. Cutlip described the results: "All calves kept
longer than one year became severely lethargic and demonstrated
clinical signs of motor neuron dysfunction that were manifest as
progressive stiffness, posterior paresis [partial paralysis],
general weakness, and permanent recumbency [lying down]." In
other words, cows infected with a sheep TSE had all the signs and
symptoms of downer cows.
Thus Hansen argues, there is considerable evidence that a TSE has
been present in some U.S. cattle for several decades.
But if mad cow disease is already present in some number of cows
in the U.S., where are the human victims? People should be
getting some form of CJD [Creutzfeld-Jakob disease], and this
disease is thought to be vary rare and not increasing in the U.S.
population. So where are the victims?
Hansen argues that CJD may be more prevalent in the U.S.
population than is presently thought. The official figures say
that CJD is exceptionally rare --one case in every million
people. In the U.S. this would mean there are 250 CJD cases at
any given time. Hansen points to two studies in which people
diagnosed with Alzheimer's were examined after death. In one
study, among 54 presumed Alzheimer's victims, 3 (or 5.5%) were
found to actually have CJD. A Yale University study of 46
victims of Alzheimer's found that 6 (or 13%) actually died of
CJD, not Alzheimer's. There are 2 million people with
Alzheimer's in the U.S. If 5.5% of them actually have CJD,
there are 110,000 cases of CJD in the U.S., not 250 cases. If
13% of the 2 million have CJD, then there are 260,000 cases of
CJD in the U.S., not 250. If even 1% of the 2 million had CJD,
it would mean there was an epidemic of 20,000 cases of CJD
masquerading as Alzheimer's. Thus the FDA's argument that CJD is
very rare, and not increasing, needs to be re-examined. [To be
(National Writers Union, UAW Local 1981/AFL-CIO)
 John Collinge and others, "Molecular analysis of prion strain
variation and the aetiology of 'new variant' CJD," NATURE Vol.
383 (October 24, 1996), pgs. 685-690. See also Adriano Aguzzi
and Charles Weissmann, "A suspicious signature," NATURE Vol. 383
(October 24, 1996), pgs. 666-667.
 S.N. Cousens and others, "Predicting the CJD Epidemic in
Humans," NATURE Vol. 385 (January 16, 1997), pgs. 197-198. See
also, David C.G. Skegg, "Epidemic or false alarm?" NATURE Vol.
385 (January 16, 1997), pg. 200.
 Lawrence K. Altman, "U.S. Scientist Wins Nobel for
Controversial Work," NEW YORK TIMES October 7, 1998, pg. A1.
 Elias E. Manuelidis and others, "Transmission to Animals of
Creutzfeld-Jakob Disease from Human Blood," LANCET (October 19,
1985), pgs. 896-897.
 Marian Burros, "U.S. Is Asked to Take New Steps to Prevent
Mad Cow Disease," NEW YORK TIMES March 28, 1997, pg. A17.
 [Michael K. Hansen], "Consumers Union's Comments on Docket
No. 96N-0135, Proposed Rule: Substances Prohibited for Use in
Animal Food or Feed; Animal Proteins Prohibited in Ruminant
Feed," February 14, 1997. Available from Michael Hansen,
Consumer Policy Institute, Consumers Union, 101 Truman Avenue,
Yonkers, NY 10703-1057; telephone (914) 378-2000.
 Lawrence K. Altman, "U.S. Officials Confident That Mad Cow
Disease of Britain Has Not Occurred Here," NEW YORK TIMES March
27, 1996, pg. A12.
 Letter from Michael K. Hansen, Consumer Policy Institute, to
Thomas Billy, Food Safety Inspection Service, U.S. Department of
Agriculture, Washington, D.C. dated May 5, 1997. Available from
Michael K. Hansen, Consumer Policy Institute, Consumers Union,
101 Truman Avenue, Yonkers, NY 10703-1057; telephone (914)
 G.R. Hartsough and Dieter Burger, "Encephalopathy of Mink. I.
Epizootiological and Clinical Observations," JOURNAL OF
INFECTIOUS DISEASES Vol. 115 (1966), pgs. 387-392.
 R.F. Marsh and others, "Epidemiological and experimental
studies on a new incident of transmissible mink encephalopathy,"
JOURNAL OF GENERAL VIROLOGY Vol. 72, Part 3 (March 1991), pgs.
 C.J. Gibbs, Jr., "Experimental transmission of scrapie to
cattle," LANCET Vol. 335, No. 8700 (May 26, 1990), pg. 1275.
 R.C. Cutlip and others, "Intracerebral transmission of
scrapie to cattle," JOURNAL OF INFECTIOUS DISEASES Vol. 169, No.
4 (April 1994), pgs. 814-820.
 Francois Boller and others, "Diagnosis of dementia:
Clinicopathologic correlations," NEUROLOGY Vol. 39, No. 1
(January 1989), pgs. 76-79.
 E.E. Manuelidis and L. Manuelidis, "Suggested links between
different types of dementias: Creutzfeld-Jakob disease, Alzheimer
disease, and retroviral CNS infections," ALZHEIMER DISEASE AND
ASSOCIATED DISORDERS Vol. 3, Nos. 1-2 (1989), pgs. 100-109.
Descriptor terms: mad cow disease; emerging diseases;
creutzfeld-jacob disease; new variant creutzfeld-jacob disease;
nvcjd; cjd; great britain; consumers union; bse; tse;
transmissible spongiform encephalopathies; scrapie; britain;
michael hansen; prions; prion theory of disease; fda; stanley
prusiner; bans; ruminants; pigs; chickens; cows; consumers union;
richard marsh; clarence gibbs; randall cutlip; alzheimer's
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