Mad Cow Disease and Humans
Rachel's Environment and Health Weekly #683
January 20, 2000
When a new form of an old human disease appeared in England
in 1995, some medical specialists immediately suspected that it
might be a human version of "mad cow disease," but they
had no proof.[1] Mad cow disease had appeared in British dairy
cattle for the first time in 1985 and during the subsequent decade
175,000 British cows had died from it. British health authorities
spent that decade reassuring the public that there was no danger
from eating the meat of infected cows. They said a "species
barrier" prevented mad cows from infecting humans. A "species
barrier" does prevent many diseases from crossing from one
species to another -- for example, measles and canine distemper
are closely related diseases, but dogs don't get measles and humans
don't get distemper.
While the British government was placing its faith in the
species barrier, British citizens began to die of a new disease,
called "new variant Creutzfeld-Jakob disease" or nvCJD.
A similar disease, CJD (Creutzfeld-Jakob disease) had been recognized
for a long time but it almost never occurs in people younger than
30; nvCJD, on the other hand, strikes people as young as 13. There
are several other differences between CJD and nvCJD, so nvCJD
represents something new. To date, nvCJD has killed 48 people
in England and one or two others elsewhere in Europe. The main
feature of both mad cow disease and nvCJD is the progressive destruction
of brain cells, inevitably leading to total disability and death.
New research published late in 1999 showed that nvCJD is,
in fact, a human form of mad cow disease,[2] dashing all hope
that a species barrier can protect humans from this deadly bovine
affliction.
Mad cow disease is formally known as "bovine spongiform
encephalopathy" or BSE. BSE is the cow version of a larger
class of diseases called "transmissible spongiform encephalopathies,"
or TSEs. TSEs can afflict sheep, deer, elk, cows, mink, cats,
squirrels, monkeys, humans and other species. In all species the
symptoms of TSEs are the same -- progressive destruction of brain
cells leading to dementia and death.
Traditional Creutzfeld-Jakob disease (CJD) is a rare human
affliction. The visible symptoms are similar to Alzheimer's disease;
in fact, CJD is sometimes diagnosed as Alzheimer's and therefore
may go unrecognized. CJD strikes one in a million people almost
all of whom are older than 55. In people younger than age 30,
CJD is extremely rare, striking an average of 5 people per billion
each year, worldwide (not counting the recent outbreak in England).
In cows, the latency (or incubation) period for mad cow disease
is about 5 years, meaning that cows have the disease for five
years before symptoms begin to appear. No one knows the latency
period for nvCJD in humans, but it is thought to be around 10
years. Because of this uncertainty, no one is sure how many people
in England already have the disease but are not yet showing symptoms.
The British government's chief medical officer, Professor Liam
Donaldson, said December 21, 1999, "We're not going to know
for several years whether the size of the epidemic will be a small
one, in other words in the hundreds, or a very large one, in the
hundreds of thousands."
The epidemic of mad cow disease was caused by an agricultural
innovation -- feeding dead cows to live cows. Cows are, by nature,
vegetarians. But modern agricultural techniques changed that.
Cows that died mysteriously were sent to rendering plants where
they were boiled down and ground up into the consistency of brown
sugar, and eventually added to cattle feed. It was later determined
that mad cow disease was being transmitted through such feed,
and especially through certain specific tissues -- brain, spinal
cord, eyes, spleen and perhaps other nerve tissues.
Ten new cases of nvCJD were reported in England in 1999, bringing
the total to 48. It has been more than 10 years since government
authorities banned the use of the particular parts of cows thought
to transmit mad cow disease. The appearance of new cases of nvCJD
in 1999 implies either that the latency period for the disease
is longer than 10 years, or that infected meat was not effectively
eliminated from the food chain when government authorities said
it was, or both.
The SUNDAY TIMES of London reported in late December that
some meat banned for human consumption is still being marketed
in England. After the mad cow scandal erupted, the British government
attempted to eradicate the disease by requiring that all cows
older than 30 months be slaughtered. As a result, by last September
more than 2.5 million British cows had been killed. But the TIMES
reported that British investigators have documented at least 50
cases of farmers and cattle dealers using bogus identity documents
to falsify the ages of cows in order to sell them for human consumption.
Furthermore, the Agriculture Ministry acknowledged that as many
as 90,000 cattle could not be accounted for. About 1600 new cases
of mad cow disease are still being reported each year in England.
In December, French health authorities announced finding a
second case of nvCJD, a 36-year-old woman in Paris. France has
continued to refuse to import British beef, even though the European
Union on August 1, 1999, formally declared British beef as safe
as any in the European Union. The European Union said in December
it will take France to the European Court of Justice to force
it to import British beef. Germany is also refusing to import
British beef.
The U.S. government says mad cow disease has never been observed
in any U.S. cows. However, a closely-related TSE disease, called
chronic wasting disease (CWD), has been increasing for almost
20 years among wild deer and elk in northern Colorado and southern
Wyoming. Since 1981, CWD has been spreading slowly among wild
deer and elk herds in the Rocky Mountains and now afflicts between
4% and 8% of 62,000 deer in the region between Fort Collins, Colorado
and Cheyenne, Wyoming.
During 1999, CWD erupted among a herd of elk on the David
Kesler Game Farm near Philipsburg, Montana, which raised elk commercially.
A few of Mr. Kesler's elk had been shipped to Oklahoma and Idaho,
and perhaps elsewhere, and CWD was discovered in some of those
animals, too. In early December, Montana health authorities slaughtered
81 elk on Mr. Kesler's farm. They initially announced plans to
incinerate the carcasses, but later decided that incineration
would be too expensive. The animals were finally buried at the
High Plains Sanitary Landfill north of Great Falls. Equipment
used to feed, water and care for the animals was also buried in
the landfill. Montana authorities announced that the fenceline
at the elk farm would be decontaminated, but they did not say
what procedure they would use. Nor did they announce what would
become of Mr. Kesler's contaminated land. The disease agent that
causes CWD -- a prion protein -- is very hardy and resists destruction
by traditional sterilization techniques like alcohol and heat.
The diseased elk carcasses in the High Plains landfill have
been buried under a mound of garbage but will still be accessible
to rainwater and perhaps to scavenging animals.
In northeastern Colorado and southeastern Wyoming, state officials
are urging hunters to protect themselves when dressing wild deer
and elk they have shot. Hunters should wear rubber gloves, minimize
contact with brain and spinal cord tissues, discard the brain,
spinal cord, eyes, spleen and lymph nodes and definitely not eat
them. There is no evidence that CWD can cross over from deer and
elk to humans, but there was no firm evidence that mad cow disease
could afflict humans until 1999, so wildlife officials in the
Rocky Mountain states say caution is warranted.
Writing in the BOSTON GLOBE, Terry J. Allen reported in late
1999 that, since 1996, Creutzfeld-Jakob disease has been identified
in 3 Americans younger than age 30.[3] All three are known to
have hunted extensively or eaten venison. There is no evidence
that CWD disease has jumped from deer or elk to humans, but the
appearance of this extremely-rare disease in young people was
the first evidence of a problem in England, so health authorities
in the U.S. say they are aggressively investigating all the possibilities.
A statistician at the federal Centers for Disease Control
(CDC) in Atlanta told Terry Allen that, if one more case of CJD
had surfaced in a person younger than 30 in the U.S., it "might
tip the balance," meaning it might convince authorities that
something truly unusual was occurring. Dr. Michael Hansen of Consumer's
Union says, "Given how rare the disease is in young people
and how difficult it is to make a diagnosis, the possibility that
some cases go undetected cannot be ruled out."[3]
Indeed, of the 3 cases detected in the U.S. since 1996, one
nearly went undetected. Last year in Utah, Doug McEwan, 28, began
to show an array of mysterious symptoms: loss of memory, loss
of motor control, mood swings, and disorientation. His wife, Tracey,
says his doctors conducted hundreds of tests but could not diagnose
his disease. She happened to see a TV program on mad cow disease
and she insisted that Doug's doctors must test for CJD. A brain
biopsy confirmed the diagnosis.
One of the three young CJD victims had eaten deer shot near
Rangely, Maine, so last November federal officials took samples
of brains from 299 deer shot in western Maine. Authorities said
at the time they were quite sure Maine deer are not harboring
CWD. So far, test results have not been released.
Federal authorities have quarantined two herds of sheep in
Vermont because they say the sheep may have been given feed that
contained parts of animals afflicted by mad cow disease. The sheep
had been imported into Vermont from Belgium and the Netherlands,
where they may have been fed improperly. A similar herd of sheep
in New York state was recently purchased by the federal government
and slaughtered.[4]
Meanwhile, a 68-year-old Indiana man with a fondness for beef-brain
sandwiches died of CJD last summer. Beef-brain sandwiches are
a local delicacy in Indiana, introduced years ago by German immigrants.
The EVANSVILLE (INDIANA) COURIER reported that John Hiedingsfelder,
a forensic pathologist in Evansville, said he had seen three cases
of CJD in the past year. No connection to mad cow disease has
been established in the Indiana cases. Roberta Heiman, a staff
writer for the EVANSVILLE (INDIANA) COURIER reportedly received
a warning from a cattleman's association not to publish any further
articles about this subject. ============
[1] Unless a specific source is cited, information in this
issue of Rachel's was taken from www.mad-cow.org, a web site maintained
by Thomas Pringle of Eugene, Oregon. Sources of information are
cited at www.mad-cow.org.
[2] Michael R. Scott and others, "Compelling transgenic
evidence for transmission of bovine spongiform encephalopathy
prions in humans," PROCEEDINGS OF THE NATIONAL ACADEMY OF
SCIENCES Vol. 96, No. 26 (December 21, 1999), pgs. 15137-15142.
[3] Terry J. Allen, "Rare, Animal-Borne Disease a Medical
Mystery; Officials Examine Maine Deer in Hunt for Clues,"
BOSTON GLOBE December 12, 1999, pg. C26.
[4] Matthew Taylor, "Mad Cow Fears, Anger on Farms; Two
Imported Sheep Herds Quarantined in Vermont," BOSTON GLOBE
October 31, 1999, pg. F24.
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