By Jon Bonné
updated 2/17/2004 9:25:52 PM ET 2004-02-18T02:25:52

A new form of mad cow disease that resembles a human form of Creutzfeldt-Jakob Disease, rather than the cow form of the illness, has been found in two Italian cows, researchers said.

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Scientists in Italy said they found the new form of the disease in two of eight samples randomly chosen from the total of 103 samples of cow brainstems in their country that tested positive for mad cow disease. The two samples had brain damage that resembled that found in the standard form of human Creutzfeldt-Jakob Disease, known as sporadic CJD, rather than the form usually found in cows, known as bovine spongiform encephalopathy (BSE) and commonly called mad cow disease.

Both BSE and the human form of CJD are fatal brain ailments caused by mutant forms of proteins known as prions, though the two are caused by different forms of the prions. Hundreds of people, primarily in England, have suffered from what is called variant CJD, a human form of BSE thought to be acquired by eating meat from infected cows.

But the team of Italian researchers found brain damage in the cows that resembled similar damage seen in human brains infected with sporadic CJD.

The findings appear to indicate that cattle, like humans, can develop a sporadic form of the disease. Salvatore Monaco, lead author of the new study, told The Associated Press it might also represent a new foodborne form of the illness.

As such, the finding highlights a long-standing mystery among researchers about the causes of sporadic CJD, which accounts for more than 80 percent of CJD cases worldwide.

While variant cases of the illness have been traced back to tainted meat, many scientists believe the sporadic form found all over the world is caused by spontaneous genetic mutation; to date, no specific cause for sporadic CJD has been documented. Because the causes of the two forms of the disease were so different, it was always assumed they should be handled as separate health concerns.

But the discovery of a new form of the disease in cattle leaves open the possibility that the sporadic form of the disease could be transmitted through food. If such a connection were to be confirmed, it could drastically change governments' risk assessments for mad cow disease.

"There's a lot of science that has to be done in order to make a link, if one exists, but it does open that concern," said Dr. Neil Cashman, a professor and researcher at the University of Toronto's Center for Research in Neurodegenerative Diseases.

However, Dr. Paul Brown of the National Institutes of Health insisted the finding does not indicate an increased threat to humans.

If a new form of mad cow disease had been affecting humans, Brown suggested, it should have been reflected in an increased incidence of CJD. Yet European scientists tracking all cases of sporadic CJD for the last decade have not found an increased incidence, said Brown, an expert in prion diseases at the National Institute of Neurological Disease and Stroke who was not part of the research team.

While just one American case of variant CJD has been recorded, and that is thought to be traced back to England, about one in a million people in the United States are found to have traditional CJD.

Similarities to human strain
Both the human and cattle diseases cause holes to form in the brain, though the precise mechanics remain a matter of some debate.

While the Italian researchers found these holes in all the samples, two cows had an accumulation of amyloid plaque in their brains, a substance often found in human neurological diseases including sporadic CJD and Alzheimer's. The researchers were surprised because the plaques had not previously been seen in cattle. They also found the prions in the two cows' brains to be similar to those found in people with sporadic CJD.

The Italians named the new form of the disease BASE, or bovine amyloidotic spongiform encephalopathy, based on mad cow disease's official acronym, BSE.

Like Alzheimer's and other degenerative brain diseases, sporadic CJD results in a gradual breakdown of neurological functions and, for most patients, death within a year of the disease's onset. There is no known cure for any form of CJD.

Monaco, of the Department of Neurological and Visual Science, Policlinico G.B. Rossi, in Verona, Italy, told the AP in an e-mail interview that he believes the incidence could be as high as 5 percent among cattle with mad cow symptoms.

The researchers, whose findings were reported Monday in the online edition of the Proceedings of the National Academy of Sciences, suggest apparently standard BSE cases be tested for the new form.

"Although observed in only two cattle," they wrote, "the BASE phenotype could be more common than expected."

However, while the new form shares similarities with human CJD, both the researchers and others who reviewed their work cautioned against assuming a link between the two.

Their finding adds another layer of complexity to a growing pile of evidence that suggests the connections between CJD and mad cow disease are not as straightforward as once thought.

In a 2002 article, British researcher John Collinge -- who helped document the similarities between mad cow disease and variant CJD in humans -- discovered that mice infected with the prions that cause mad cow disease developed both the variant and traditional forms of CJD.

Brown noted there have been unpublished reports from Japan of cows with a different form of mad cow disease. And in 1998, three of the Italian researchers even documented a case of CJD in an Italian man whose cat was simultaneously stricken with a feline form of the disease.

'More suspicious'
The precise source of BSE is so crucial because it dictates how governments respond to prevent further human cases of mad cow disease.

Cattle are believed to develop BSE from eating infected tissues of other animals. That feed has now been banned in many countries, including the United States -- which in 1997 banned its use on cows and some other livestock but still allows it on certain animals.

However, Cashman noted, the Italian scientists' discovery resurfaces earlier considerations that the first case of BSE might have formed spontaneously, rather than a result of feeding cattle protein to other cows, as has been suspected.

Similarly, Dr. Michael Hansen, who researches prion diseases for Consumers Union, said the new findings cast additional skepticism on the long-held notion that all mad-cow cases stem from the same aberrant prions uncovered in British cattle. The clear line generally drawn by researchers between the sporadic and variant forms may be more difficult to maintain.

"People always thought it strange that all these cases of mad cow so far were one strain," Hansen said. "It doesn’t prove anything, but it's more suspicious. We need to pay more attention to all forms of CJD," not simply the form tied to mad cow disease.

Questions about testing
The findings, and the recommendation for broader testing, are likely to raise new questions about the current methods to detect BSE.

Authorities discovered the first U.S. case of mad cow disease last December in a Washington state dairy cow imported from Canada. The cow was one of 20,000 tested by American officials in 2003, in a surveillance program that mostly focused on injured and sick cows.

This year, the U.S. Department of Agriculture plans to test 40,000 head of cattle for mad cow disease, out of some 35 million slaughtered annually. The testing levels, while in compliance with international guidelines, fall far short of testing regimes in many other countries.

The Italian scientists, for example, discovered the aberrant cases through the use of rapid BSE testing kits used to test 1.6 million Italian cows between January 2001, when the Italian government mandated testing on all older cattle, and August 2003.

Calls have increased in recent weeks for the use of rapid tests and of more widespread testing on the U.S. herd. A panel of House lawmakers Tuesday told the U.S. Department of Agriculture that it needed to expand its testing to at least 200,000 head of cattle.

The USDA has said the current plans for testing are sufficient. It announced Feb. 9 that it had ended its probe to find other suspect cattle from the same birth herd as the infected cow, finding only 14 of the 25 cows considered at highest risk.

While American testing procedures remain focused on sick cattle, the researchers in Italy did not indicate that the cows in the study exhibited outward signs of illness at slaughter. However, they were 11 and 15 years old -- older than most cattle intended for human consumption. Researchers also hope to find out more about the effects of aging on BSE and related diseases.

The Associated Press contributed to this report.


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