SEATTLE POST-INTELLIGENCER seattlepi.nwsource.com156393 madcow13.htmlOpen ↗ Mad cow
danger may even be bigger
Research suggests sick animals may not show symptoms
Tuesday, January 13, 2004
By TODD HARTMAN SCRIPPS HOWARD NEWS SERVICE
Below the drumbeat of reassurances from government and the cattle industry that the meat supply
remains safe despite this one case of mad cow disease, a small universe of scientists working on a
family of related illnesses is finding disturbing evidence to the contrary.
Several studies, including research at a government laboratory in Montana, continue to spark
questions about human susceptibility not only to mad cow, but also to sister diseases such as
chronic wasting disease, which mainly affects deer and elk, and scrapie, which infects sheep.
Mice research and clusters of cases in which humans contracted a disease similar to mad cow also has
a few scientists wondering whether consuming infected meat might have killed far more people than
medical experts have long assumed, not only in Great Britain, but in the United States as well.
Most scientists believe the relatively small number of known human cases, called Creutzfeldt-Jacob
disease, strongly indicates this disease -- whatever its cause or origin -- is rare and difficult to
transmit. There is also no evidence yet that scrapie in sheep or chronic wasting disease in deer has
ever been passed to humans.
But some scientists say it's possible that chronic wasting, endemic in Colorado's wild deer and
elk, has sickened and proved fatal to humans. These experts challenging the standard view note
that doctors haven't -- or can't -- recognize signs of these other forms of the disease during
an autopsy.
Little of this research reaches the broad public audience, leaving most people to hear only the oft-
repeated promises of well-funded interest groups or high-profile public officials.
Just last week, for example, the National Cattlemen's Beef Association described mad cow disease
solely as an animal and economic problem -- not a human health problem. The U.S. Department of
Agriculture has said repeatedly that the nation's beef supply is safe.
Such statements, offered frequently since the December discovery of a Holstein with mad cow
disease in Washington state, spark criticism from some scientists and consumer advocates who say
that the government and industry are injecting certainty into a field where uncertainty remains
the dominant theme.
Much remains unknown about so-called transmissible spongiform encephalopathies, or TSEs, the family
of diseases to which mad cow, scrapie, chronic wasting disease and two human versions -- known as
Creutzfeldt-Jakob, or CJD, and "new variant" CJD -- belong.
This rogues' gallery of deadly illnesses features an array of frightening symptoms. In humans they
can include depression, inability to conduct simple tasks such as operating a telephone and loss of
balance and speech. In every case, the victim's brain becomes riddled with holes; thoughts, emotions
and memories disappear on the way to death, often in just a matter of months.
But much about the diseases remains a mystery.
Clusters of a rare disease
It's long been believed, for example, that only one of the two versions of human CJD can be linked
to eating meat contaminated with mad cow disease. The other version, known as sporadic or classical
CJD, has long been thought to occur randomly in about one in every million people, a distinctive
illness with no link to meat from an infected animal.
But a few studies in the past three years have challenged that view, suggesting that classical CJD,
might, in some cases, also result from eating contaminated meat.
Scientists in Great Britain injected tissue from a cow with mad cow disease, also known as bovine
spongiform encephalapothy, into mice whose brains were genetically engineered with human genes. One
set of mice fell sick with the human form of mad cow, or new variant CJD.
But, in a finding that stunned researchers worldwide, another set of the genetically altered mice
developed what looked like the sporadic form of CJD, the one scientists have long believed has no
relationship to mad cow disease or meat-eating.
"This finding has important potential implications as it raises the possibility that some humans
infected with (mad cow disease) may develop a clinical disease indistinguishable from classical
CJD," the researchers wrote in November 2002.
French scientists a year earlier found a strain of scrapie, the version of the disease that infects
sheep, also caused brain damage in mice similar to classical CJD.
Though these findings run counter to most studies, the two studies suggest that some of the hundreds
of Americans who contract classical CJD each year could have been infected by mad cow-contaminated
meat, and not simply by biological bad luck.
Then there are the mysterious clusters of human cases. Because classical CJD is so rare, scientists
don't usually expect it to occur in clusters. But such clusters have occurred, including among
hunters eating venison.
The most recent example involves seven people who apparently died of classical CJD in New Jersey.
All of them had a link with a racetrack in Cherry Hill where they ate, according to reporting this
month in The Philadelphia Inquirer.
Most surprising: The deaths included a 29-year-old. It's extraordinarily rare for someone so young
to die of classical CJD. Victims are typically older than 55. In contrast, victims of new variant
CJD in the 1990s mad cow panic in England were often young people.
The U.S. Centers for Disease Control and Prevention wasn't initially interested in the cluster, but
since the discovery of the case of mad cow in Washington state the agency is taking another look at
the case, according to The Inquirer.
CJD may be underreported
Even so, experts caution that clusters can also be coincidences. Rare diseases don't always end up
geographically spread out.
"The cluster is curious, but these sorts of things can happen by random chance," said Patrick
Bosque, a neurologist at Denver Health and an expert on TSE.
Bosque is open-minded about the possibility of humans contracting such diseases at a higher rate
than is currently believed, but is also cautious about jumping to conclusions.
"With almost 300 cases of CJD expected in the U.S. each year, it isn't too surprising that over
a few years one might occasionally find a cluster associated with some ill-defined event or
place," he said.
But some scientists believe the true number of U.S. CJD cases is underreported, and the disease is
not as rare as once believed. Some experts believe that it is possible that some cases diagnosed as
Alzheimer's could actually be CJD. Some other dementia-like diseases could also be misdiagnosed,
experts say.
"Given the new research showing that infected beef may be responsible for some (classical) CJD,
thousands of Americans may already be dying because of mad cow disease every year," wrote Dr.
Michael Greger, a physician and vegan advocate.
Many scientists, however, caution that if mad cow disease were really fueling an increase of
classical CJD in the United States, then we should also be seeing many more cases of new variant
CJD, the form of mad cow disease that struck people in Great Britain.
Even in Britain, where millions of people were estimated to have eaten mad cow-contaminated meat,
fewer than 150 people came down with new variant CJD.
"Could BSE have been transmitted to people in the U.S. but gone unrecognized because it looked like
(classical) CJD?" Bosque said. "I suppose it is possible, but there would be no obvious explanation
for the fact that (new variant) CJD has not been seen in the U.S."
But the critics answer that the United States has no formal monitoring system in place to track CJD
cases and autopsy the victims. That would enable scientists to more accurately detect trends in
occurrences and study the pattern of destruction in the brain that reveals whether a victim died of
classical or new variant CJD.
TSEs borne by silent carriers
At a National Institutes of Health laboratory in western Montana, researchers are focused on the
question of what happens when TSEs move back and forth between different animals. What they've found
is unsettling.
Their latest research is an extension of work they've been conducting for several years. It shows
that TSEs can be passed to some animals without causing disease, but then passed onto another
species where they cause illness.
The implications are significant.
Researchers began by taking brains of hamsters infected with scrapie and injecting that tissue into
mice. Then, they killed the mice at various points and tested for presence of the infectious agents
-- called prions -- in the brains of mice. They didn't find any.
But researchers took the next step, injecting tissues from these apparently prion-free mice into
another set of healthy mice and hamsters. That's when the outcome turned frightening: the newly
infected creatures developed TSEs and died.
What does it mean? The mice from the earlier part of the experiment were not free of the disease
after all. They were silent carriers of a sort, not showing any signs of the illness but able to
infect others.
This could have dramatic implications for the real world. What if, for example, some humans carry
mad cow disease or another TSE, but aren't affected by it? Perhaps they could still pass it on
through blood transfusions or transplants. In the words of researchers: "Subclinical human carriers
might pose a serious risk for contamination of surgical instruments, tissue transplants and blood
products," according to a 2002 report on the mice-hamster experiments in Montana.
Then there are the ramifications for animals.
Michael Hansen, a scientist for Consumers Union, points out that cattle tissues that are mostly
removed from the human food chain are still converted to feed for chickens and pigs, among others.
Remains of those animals, in turn, are still rendered into cattle feed -- a practice derided by
critics and banned in Europe, but still legal and common in the United States.
"Those animals could become silent carriers and infect cattle," Hansen said.
The Montana researchers have continued their work, injecting tissues from the mice and hamsters that
became sick into yet another set. The next generation of mice and hamsters got sick as well.
The experiments have also revealed another disturbing fact.
The infectious prions appear to persist and adapt, evolving to infect a new species and even
becoming more virulent as they move between species. In some cases, incubation periods change,
growing longer or shorter depending on the experiment.
In short, behavior of the diseases has been unpredictable, making statements of certainty about them
untenable.
Bosque, the Denver neurologist, said the ability for TSEs to hide inside some animals and increase
their infectivity is worrisome.
"It raises an additional level of concern, that these prions can persist in animals, and increase,
even though (the animals) don't appear sick," Bosque said. "For one thing, it shows you that
screening for just obviously sick animals may not be sufficient."
But currently, the United States focuses its testing almost solely on sick or "downer" animals.
Industry officials have said testing every cow for mad cow disease as Japan does would be a waste of
time and money.
DEFINING DISEASES Several similar brain-wasting diseases affect livestock and wild animals:
* Mad cow disease: Also known as bovine spongiform encephalopathy, this disease infects cattle.
Infectious proteins called prions kill brain cells, causing spongelike holes to develop. First
identified in Europe in the 1980s.
* Chronic wasting disease: This illness infects deer and elk. No cases of transmission to hunters
eating the meat have been confirmed.
* Scrapie: This spongiform disease is found in domesticated sheep.
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P-I reporter Tom Paulson contributed to this report.
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