The Mad Cow Connection; If a Cattle Disease Could Leap the 'Species Barrier' into People,
is Colorado's Wildlife Disease the Same Time Bomb?

June 1, 2002 Rocky Mountain News (Denver, CO) by Lou Kilzer
It began with what his father thought was another bout with asthma.

Steve Churchill - a tall, lanky English 18-year-old who longed to join the Royal Air Force - had suffered attacks in the past and his father, David, paid it little attention this time.

But looking back on that June day in 1994, David Churchill knows how wrong he was. "These asthma attacks were more likely to have been panic attacks, which can be one of the first symptoms of the disease that was soon to afflict our son," he wrote in a statement.

Steve Churchill was to become the first human being to die of a new disease that would soon panic the United Kingdom - variant Creutzfeldt-Jakob disease (vCJD), better known by its bovine relative, mad cow disease. No one knew a thing about vCJD as Steve slowly descended into the depths of the bizarre illness, leaving his family desperate, confused and ultimately angry at the British government's inability to see it coming.

The government's formal position, in fact, had been that humans were safe from mad cow, that the disease could not break the "species barrier." That is, it could not cross from one species, cows, to the other, humans.

Both mad cow and vCJD belong to a family of fatal maladies called transmissible spongiform encephalopathies (TSEs), which also include scrapie in sheep and chronic wasting disease in deer and elk.

Steve Churchill had always been bright, but soon after the asthma episode he began having troubles with his studies. On the 26th of August 1994, the mechanically gifted pilot-in-training inexplicably crossed into the approaching lane on a highway and collided with an Army truck.

Then came the depression.

Described by his sister, Helen, as having been "the life and soul of any party," Steve grew morose and uncommunicative. On Oct. 19, his parents found a letter in his room discussing his deep sorrow for "not being able to cope with life."

The Churchills sought psychological help, and Steve soon began taking drugs for depression.

But the symptoms worsened and Steve developed elaborate hallucinations and began to lose short-term memory.

Christmas had always been his favorite time of year, but Christmas 1994 was different.

"I bought him a pair of fluffy gorilla slippers, which, to my horror, quite frightened him," his sister would recall.

The slippers weren't the only things that frightened Steve. While watching the children's movie Black Beauty, he became agitated, thinking he was the youngster under threat. Watching Baywatch, Steve became convinced he was drowning.

What his father called Steve's "daymares" increased, and his coordination began to vanish. He could no longer write his signature, and his gait became staggering.

On Feb. 13, 1995, doctors told the Churchills that Steve had some sort of degenerative neurological disease and for the first time they heard a new term - CJD, short for Creutzfeldt-Jakob Disease.

David Churchill took sick leave from his fireman's job to be with his son.

But there would be no more good days.

Steve Churchill died at 9:41 p.m., May 21, 1995. He had just turned 19.


It would not be until the next year that scientists shocked the world with an announcement that Steve Churchill and nine other young Britons had died from a disease officials had said for a decade could not be transmitted from cows to humans.

Even today, very little is known about what most scientists say is the cause of the disease - a mutant protein called a prion.

But scientists now know what was likely happening inside Steve Churchill's brain both before and after his "asthma" attack signaled the onset of his inevitable decline from first symptoms to death.

Sometime before the summer of 1994, Steve had probably eaten ground meat that contained brain or spinal tissue from a cow suffering from mad cow disease - bovine spongiform encephalopathy, or BSE.

This disease was first diagnosed in British cattle eight years before Steve Churchill crossed the centerline and wrecked his mother's car.

By the time Steve's symptoms appeared, prions had built up in his brain to the point where microscopic holes likely began forming in neural tissue, according to scientists who've studied the disease.

TSEs can be traced back to the 1700s, when sheep were first noticed wobbling, withdrawing and scraping themselves against fences as though trying to relieve a great itch. Called scrapie, the disease is caused by a dozen or more strains of infectious prions.

TSEs also naturally occur in about one in a million humans a year, with the most common form called sporadic Creutzfeldt-Jakob Disease, or simply CJD.

There is no evidence that scrapie has ever infected a human and only in the cases of cannibalism in a New Guinea tribe and contaminated surgical tissue or instruments has CJD spread from human to human.

Those facts gave researchers a false sense of security, at least as pertaining to mad cow. It simply wasn't believed that it could cross the species barrier into humans.


In 1967, deer held in a Colorado Division of Wildlife pen in Fort Collins began dying after a period of strange behavior. Ten years later, researcher Beth Williams took a slice of deer brain and looked at it under a microscope.

She noticed the spongiform change immediately, identifying chronic wasting for the first time as a TSE disease.

But in 1977 there were no loud calls of alarm about this new TSE in wildlife. "It was mostly thought to be academic," said National Institutes of Health prion researcher Richard Race.

Scientists believed that the TSE in deer and elk would behave like scrapie, infecting only deer and elk and not jumping into other species.

But the alarms began sounding in 1986 when British cattle suddenly started coming down with BSE.

After an investigation, epidemiologists said the most likely way cattle first were infected with the disease was when a sheep with scrapie was slaughtered and sent to a rendering plant. Brain tissue, some internal organs and bones were converted into meat and bone meal and fed back to cattle.

That was the spark.

Then carcasses of infected cattle were rendered and fed back to other cattle, creating an exponential increase of disease.

Eventually over 180,000 cattle in Britain and Europe were infected and over 4.5 million were destroyed to contain the epidemic.

The theory of the cause of BSE set off sirens in the scientific community. A TSE had somehow gone from sheep to cattle. The belief in an absolute species barrier for prion disease was shattered.

Many people in England began wondering: If the disease could spread from sheep to cows, could it then continue from cattle to humans?

The answer they were told repeatedly was "no." Humans had lived for hundreds of years with scrapie-infected sheep without becoming infected. There was no reason to suspect that a similar disease in cows would be any different, officials said.

When reassuring words did not convince the public, British Agriculture Minister John Gummer went before cameras with his 4-year-old daughter so that the two could munch on hamburgers.

Eating beef, he said, was "perfectly safe."

Then Steve Churchill and nine others began their death march.

At a tension-filled press conference on March 20, 1996, red-faced British officials admitted that they had been mistaken. BSE had spread to humans after all.

Suddenly, interest in prions skyrocketed and many began to cast a wary eye on the related illness first detected in Colorado - chronic wasting disease.

Could it also jump the species barrier?


What are prions and why do they behave so badly?

Naturally occurring in all mammals, the function of prion proteins is little known. But it's after they mutate into rogue shapes that scientists really get confused.

The pioneer in prion research is a University of California at San Francisco neurologist named Stanley Prusiner, an iconoclast who thought so far outside the box that colleagues thought he was perhaps mad.

Prusiner proposed that TSEs were caused by a protein that managed to replicate itself without the use of genetic material like DNA, the basic template for protein production.

The notion was scoffed at and dismissed. Everyone knew replication depended on chromosomes and genes, which are made of DNA. A lowly rogue protein was hardly fit for this kind of endeavor.

Self-replication was unheard of, said the critics. It was impossible.

That was in the early 1980s.

The laughs had died down by 1997 when Prusiner went to Stockholm to accept the Nobel Prize in Medicine.

Though there are a few holdouts among researchers who still believe there must be a genetic base for prion disease, most today accept what Prusiner found nearly two decades ago. Prions are the causative agent of TSEs, and they have developed a novel way of replicating.

The main evidence ruling out DNA's involvement in TSE is the amazing toughness of the infectious prion.

Separated out from other cell components, infectious TSE-causing material can withstand temperatures to 1,100 degrees. Prions are little disturbed by ultraviolet light. Most disinfectants leave it unharmed.

DNA could not easily survive any of the above. Prion protein does.

"Ten years ago the protein guys were the crazy guys," said NIH researcher Race from his laboratory in Hamilton, Mont. "Nobody believed them. Now the pendulum has swung to the other side where the protein guys are on top."

Left unanswered is how this hearty little protein replicates.

Prusiner theorizes that a so-far unknown substance he calls "Protein X" is involved in the process, but there are competing theories, including some holdouts who believe DNA is involved.

Deeper still is the mystery of how prions of one species can cause those of another to malform.

When a human gets vCJD by eating cows infected with BSE, he doesn't inherit the BSE prion. Instead, the BSE prion induces a human prion to change shape, and that newly shaped prion slowly induces other human prion protein to misshape in a chain reaction that leads to disease after 5 to 15 years.

It's the molecular shape of the prion protein that is important. Infectious prions retain the exact same sequence of amino acids - the same basic structure - as those that occur naturally.

That fact makes the disease even more insidious. The immune system is geared to fighting pathogens that it recognizes as "non-self." But the prions are recognized as self, so there is no immune response to TSEs.

There is, however, at least one shield against the human form of mad cow disease. So far, all 130 humans who have contracted the disease have an amino acid sequence found in only 38 percent of the population.

The majority of humans are apparently immune.

Scientists are looking at CWD for similar patterns, asking if any molecular patterns in livestock or human prion proteins might predispose them to infection.

Researchers are wary of CWD for other reasons, as well. Deer and elk can be infected for several years before it can be detected from their behavior.

For the long incubation period, the infected brain would even look healthy under the microscope, which was the standard test for CWD for many years.

Now a more sensitive chemical test is used that researchers believe can detect the disease within six months of infection. A new experimental test shows promise of detecting the disease after 42 days.

CWD is also worrisome because it - unlike BSE - is infectious in nature and spread from animal to animal by deer and elk, perhaps even by nose-to-nose contact.

With BSE, a cow or human actually has to ingest infected tissue. Not so in deer. Ninety percent of deer kept in a Fort Collins pen for two years developed CWD.

The disease is apparently much less virulent in the wild. But if CWD were to jump species and if the rogue prions in the new host species were to inherit this high infectivity among those in close proximity, it could mean that an inevitably fatal disease would be as infectious as the flu, a nightmare scenario.

Paul Brown, former head of the U.S. Food and Drug Administration's TSE Advisory Committee, has said he is most concerned about the disease possibly crossing over into livestock, with crushing economic impact. There is no proof in current studies that it can cross.

The TSEs are confounding scientists in other ways as well. Some of them seem to be changing. Incubation periods in some are declining. Symptoms are evolving.

There are cases where a TSE causes very little spongiform change, but still causes illness.

And some new research suggests the bovine TSE, mad cow disease, may have spread to far more people than has been estimated.

That study involves the possible existence of stealth prions that can sit in wait in one animal before springing lethally into the next.


Some of the most intriguing scientific research into prion disease is taking place in Hamilton, Mont. - population 3,705.

Hamilton's Rocky Mountain Laboratories, a part of the National Institutes of Health, was in the TSE business even before Prusiner developed his theory. Researchers there began examining scrapie in the 1950s and then picked up with BSE and now are concentrating resources on chronic wasting disease.

In a paper written nearly two years ago, the lab's Gregory Raymond and other researchers gave ammunition to both sides of the issue - to those who are alarmed by CWD and those who downgrade its possible impact.

Prions from CWD-infected animals were weak in converting human prions into deadly misshapes, based on laboratory tests. In the test tube, human prions were much more resistant than those naturally occurring in elk and deer.

Mike Miller, the top veterinarian for the Colorado Division of Wildlife, takes the position that these results demonstrate a species barrier and that there is no evidence that CWD is infective to humans.

"There is no support that it is at all possible," he said in a recent interview.

Michael Hansen, a scientist for Consumers Union, the publisher of Consumer Reports, says there's no proof that it can't.

Hansen's camp said Raymond's study found that the rate at which CWD prions infected human prions in the test tube was almost identical to the rate that BSE prions did so.

And BSE can definitely spread to humans.

Advocates for the position that CWD might cross the species barrier point to three people under 30 who came down with a TSE after eating venison. They point out that it is extremely rare to find naturally occurring CJD in people that young - in one 17-year period in the United States ending in 1996, there were only four cases of sporadic CJD among those under age 30. Between 1996 and 2000, there were four more cases.

One CJD victim was a 28-year-old woman who ate elk that a relative said could have come from Wyoming. Another victim was a 29-year-old Utah man who became ill after hunting in areas of Wyoming not thought to have elk infected with CJD.

The third victim, a 27-year-old man, hunted in neither Colorado nor Wyoming, though he had his meat butchered at a plant that handled 20 elk a year from Colorado.

Ermias Belay, a scientist at the Centers for Disease Control in Atlanta, said brain specimens of the three did not resemble those of vCJD victims in Britain and Europe, who became infected by ingesting mad cow-diseased beef. He concluded that there was "no strong evidence" of a link to CWD.

But Brown, the former FDA official, has said no one knows how a human brain infected with CWD might look. He has called for research in primates to find out.

Such research is expensive and funds are few, said Belay, an epidemiologist.

Raymond's research in the NIH's lab in Hamilton isn't the only study there causing controversy and concern.

Late last year Richard Race and colleagues published a paper in Virology that demonstrated how bizarre TSEs can be.

Researchers took brains of hamsters infected with scrapie prions and injected the neural tissue into mice. The mice were killed at various intervals and tested for the mutant prions. Every test failed to find a continuing replication of prions. They didn't have any.

To further research these apparently prion-free mice, Race took brain matter from these healthy mice and injected it into other healthy mice and hamsters.

The newly infected mice and hamsters developed TSEs and died.

That means, Race said, that the mice from the first part of the experiment were not prion-free after all.

"That's the part that worries everybody," he said. "It says there could be all types of asymptomatic carriers around and we don't have an assay sensitive enough to pick it up."

The possible implications?

"There's no good way to test this, but it's possible that the number of people in Europe that were possibly infected with BSE could be far, far greater than most people have generally considered.

"We might have thousands, or hundreds of thousands or even millions of these carriers having very, very low levels of (rogue prions) replicating in their brains."

If, as in the test mice, the prions get more virulent as they pass from one animal to the next, they might show up as full-blown disease in someone who has - for example - received a blood transfusion from the person originally infected.

At present, though, prions are not known to be in blood.

Or the disease might spread through contaminated surgical instruments.

In March of last year, Denver's Exempla St. Joseph Hospital announced that six patients may have been exposed to a deadly prion after they underwent surgery in which instruments were used that had been previously used on people later diagnosed with Creutzfeldt-Jakob disease.

Exempla now uses disposable instruments in undiagnosed brain biopsies and in known CJD cases. The national Joint Commission on Accreditation of Healthcare Organizations sent out an alert last summer urging similar practice by its 5,000 member hospitals.

Other recent research by Prusiner and Denver neurologist Patrick Bosque is also raising alarms. They found that in lab mice infected with a TSE, high levels of prions are detected in certain muscle groups.

For years, the prions were thought to be confined mostly to the brain and spinal cord. The research could mean that scientists must look further. Prusiner has called for the testing of muscles in infected deer, elk and cattle.

Simply put, muscle is meat, the part consumed by humans.

What does it all mean?

The problem, as with so much in this strange disease, is that so much remains to be discovered.

Says Race: "No one knows the full range of the human implications."


After Steve Churchill died in 1995, his family pressed for an investigation, so rare it was for someone to die of normally occurring CJD at 19. The median age for people suffering CJD is 68.

"No one in authority would accept that Steve's death was different to any other young person's death," his father later complained. "We were voices in the wilderness."

Local health officials declared that there was no need to look into Steve's death.

In September 1995, four months after his son died, David Churchill returned to his fireman's job, but he didn't stop the fight for an inquiry.

And when the fateful announcement was made on March 20, 1996, that Churchill had died of a variant form of CJD, the father didn't feel so much vindicated as determined to press on.

David and Dot Churchill formed the Human BSE Foundation to lobby hard on behalf of vCJD sufferers and their families.

"We had no option," said Churchill. "We were the first in the field."

In the end, Churchill said the world knew that the family had been right and the establishment had made mistakes.

"We are not cranks," he said, "but just grieving parents that need the truth behind the premature, untimely and unnatural death of our son explained to us."

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