New Research Indicates Human Form of Mad Cow
More Complex than First Thought

CHRIS MORRIS / Canadian Press 18jan04

New research suggests that the human form of mad cow disease is a lot more complicated than originally thought, and, potentially, much scarier.

Scientists have long agreed that eating cattle tissue infected with bovine spongiform encephalopathy - mad cow disease - can cause the human form of the disease, known as variant Creutzfeld-Jacob disease.

But recent animal tests indicate that eating infected beef may also cause another form of the disease, classical CJD, forcing scientists to re-examine assumptions about the nature of the deadly disease and raising fears that it may be more widespread than previously thought.

"We have to be a little bit open-minded about this," says Dr. Laura Manuelidis, professor and head of neuropathology at Yale University in Connecticut.

"There are certain things we don't know and we can't be absolute about. We can't make believe it's a cut-and-dried situation."

The accepted wisdom has been that classical CJD has nothing to do with mad cows. It affects older people, those over 55, and generally occurs spontaneously at the rate of about one person per million per year.

It has been confused with Alzheimer's disease and there is some concern that because of misdiagnosis, it may be more widespread than the confirmed numbers indicate.

"The fact is in the United States, the autopsy rate has gone way down from when I was a medical student, even in academic centres," says Manuelidis.

"If you don't examine the brains, how can you possibly know what you are missing?"

New variant CJD, the form that has ravaged Britain since 1995, affects people at a much younger age, normally in their 20s and 30s. It is widely believed that only this form can be triggered by consuming infected meat.

Both forms riddle the brain with holes, causing dementia and, ultimately, death.

Manuelidis says a recent study in Britain involving mice whose brains were genetically engineered with human genes gives weight to her long-held theory that classical CJD may be more insidious than assumed.

The mice were injected with tissue from mad cows. One set of mice fell sick with the human form of mad cow, or variant CJD.

But, in a finding that shocked researchers, a few of the mice developed what looked like classical CJD, the form scientists have long believed had no relationship to mad cows or eating meat.

Dr. Neil Cashman, a professor of medicine at the University of Toronto, describes the findings as "striking and worrisome."

The question is, could an epidemic of classical CJD be lying dormant in the brains of people who have eaten infected cattle products - specifically products containing brain or spinal cord matter?

Cashman says data from Britain shows that the incidence of classical CJD remained stable during the variant CJD epidemic in that country, which killed 146 people.

However, there still could be trouble down the road.

"The huge exposure of the U.K. population to BSE prions has clearly resulted in an epidemic of variant CJD," Cashman says.

"There may be another one brewing down the road of classical CJD, but it hasn't been seen yet."

Manuelidis says it is the future that's worrisome.

She hopes fellow researchers will open their minds when it comes to CJD.

"It worries me when people get very absolute about these things," she says.

"The CDC (Centers for Disease Control in Atlanta) didn't listen to me when I said, 'Why are you just looking at people under 40 years old (for variant CJD)? What makes you think that someone who is older is not going to get this?' Fine, it's obvious that it shouldn't have been in those younger people in such numbers. But the older people who get it may not show the same lesions."

Manuelidis says there may be people walking around who have the infectious BSE agent, possibly in high enough levels to be transmissible through blood transfusions or organ donations, but not show signs of the disease and perhaps not show signs of the disease for a long time.

"There is a case now in England linked to a blood transfusion, someone who got (variant) CJD in a blood transfusion from a patient who was perfectly fine, but is now confirmed to have variant CJD," she says.

"This is the issue."

Cashman says that looking at the situation in North America, where there have been only isolated mad cows and no home contracted cases of variant CJD, he doubts there are yet any cases of classical CJD caused by BSE infection.

"It's extremely unlikely because we have seen no variant CJD here," he says.

Still, Manuelidis says both the United States and Canada should improve their investigation and reporting of CJD cases to get a better handle on its occurrence.

source: http://www.canada.com/health/story.html?id=09BD36FE-6CC8-4854-8A49-12E23A6A7D8E 19jan04