Very interesting theory:
One plausible mechanism is a virus interacts with normal prions and causes them to assume an abnormal shape, which is how TSE diseases damage brain cells. The virus theory would help explain why only certain individuals become ill with these diseases. Not all mice with mutated prions fall ill. It also could be having abnormal prions makes people vulnerable to infection with the virus, the NIH scientist speculated.
Manuelidis and the NIH researcher conceded, however, efforts to develop treatments based on prions might not be entirely futile because the abnormally folded proteins appear to play some role in the diseases. Safar pointed out antibodies and other agents that block prions have had some success in stopping the progression of TSEs.
That also means the prion-based diagnostic tests being developed also might be useful because detecting misfolded prions does indicate the presence of the diseases. Still, if they are caused by a virus or bacteria, being able to find the infectious organism would enable faster detection of the diseases and, if a treatment is developed, initiation of medication before the brain is damaged.
Safar's group is developing a test that can detect the disease soon after infection. Early detection is critical because if the disease is not detected until advanced stages, it is too late to prevent or reverse the brain destruction, he said.
One alternative idea that has received NINDS funding is a small project by Bastian. He has uncovered evidence a nanobacteria could play a role in causing TSEs. The grant is only $185,000, however, a far cry from the millions heaped upon researchers focusing on the prion concept.
Yet Bastian has made progress. He presented research at the American Association of Neuropathology meeting in Orlando in May showing DNA from a type of bacteria carried by many insect species -- spiralplasma -- can be found in brains of people with CJD and in sheep brains infected with scrapie. The bacteria cannot be found in normal, healthy brains.
The bacteria, found in ticks and mosquitoes, also have been shown to cause a type of spongiform disease in rats and mice, Bastian said. "There's really clear evidence that there's an association of the bacteria with this disease," he said. He said he suspects the bacteria could cause prions to mutate and fold abnormally, and this could cause the brain destruction.
To Bastian, the idea that a bacteria carried by insects cause these diseases fits with what currently is known about how they are transmitted. One unexplainable phenomenon about scrapie in sheep is the animals can catch the disease without having contact with infected individuals. To explain this, some researchers have proposed the disease can arise spontaneously. However, sheep in New Zealand display no evidence of the disease -- yet they should have experienced at least a few cases if it arises spontaneously.
If TSEs are transmitted by insects, Bastian explained, and if the insects in New Zealand do not carry the bacteria, this would explain why sheep in that island country are free of the disease. The insect/bacteria hypothesis also fits with the pattern of bouts of chronic wasting disease seen in deer and elk in the Midwestern and western United States. Animal researchers there have been baffled by the disease, which appears to jump from herd to herd even though the animals do not come into contact with one another.
Bastian hopes to develop a screening test for scrapie, human CJD and chronic wasting disease in the next few months based on the spiralplasma bacteria. If his theory is correct, and the test works, he said it would go a long way toward detecting those infected and perhaps help elucidate the role prions play in these dangerous diseases.
Steve Mitchell is UPI's Medical Correspondent. E-mail sciencemail@upi.com
Copyright © 2001-2004 United Press International
One plausible mechanism is a virus interacts with normal prions and causes them to assume an abnormal shape, which is how TSE diseases damage brain cells. The virus theory would help explain why only certain individuals become ill with these diseases. Not all mice with mutated prions fall ill. It also could be having abnormal prions makes people vulnerable to infection with the virus, the NIH scientist speculated.
Manuelidis and the NIH researcher conceded, however, efforts to develop treatments based on prions might not be entirely futile because the abnormally folded proteins appear to play some role in the diseases. Safar pointed out antibodies and other agents that block prions have had some success in stopping the progression of TSEs.
That also means the prion-based diagnostic tests being developed also might be useful because detecting misfolded prions does indicate the presence of the diseases. Still, if they are caused by a virus or bacteria, being able to find the infectious organism would enable faster detection of the diseases and, if a treatment is developed, initiation of medication before the brain is damaged.
Safar's group is developing a test that can detect the disease soon after infection. Early detection is critical because if the disease is not detected until advanced stages, it is too late to prevent or reverse the brain destruction, he said.
One alternative idea that has received NINDS funding is a small project by Bastian. He has uncovered evidence a nanobacteria could play a role in causing TSEs. The grant is only $185,000, however, a far cry from the millions heaped upon researchers focusing on the prion concept.
Yet Bastian has made progress. He presented research at the American Association of Neuropathology meeting in Orlando in May showing DNA from a type of bacteria carried by many insect species -- spiralplasma -- can be found in brains of people with CJD and in sheep brains infected with scrapie. The bacteria cannot be found in normal, healthy brains.
The bacteria, found in ticks and mosquitoes, also have been shown to cause a type of spongiform disease in rats and mice, Bastian said. "There's really clear evidence that there's an association of the bacteria with this disease," he said. He said he suspects the bacteria could cause prions to mutate and fold abnormally, and this could cause the brain destruction.
To Bastian, the idea that a bacteria carried by insects cause these diseases fits with what currently is known about how they are transmitted. One unexplainable phenomenon about scrapie in sheep is the animals can catch the disease without having contact with infected individuals. To explain this, some researchers have proposed the disease can arise spontaneously. However, sheep in New Zealand display no evidence of the disease -- yet they should have experienced at least a few cases if it arises spontaneously.
If TSEs are transmitted by insects, Bastian explained, and if the insects in New Zealand do not carry the bacteria, this would explain why sheep in that island country are free of the disease. The insect/bacteria hypothesis also fits with the pattern of bouts of chronic wasting disease seen in deer and elk in the Midwestern and western United States. Animal researchers there have been baffled by the disease, which appears to jump from herd to herd even though the animals do not come into contact with one another.
Bastian hopes to develop a screening test for scrapie, human CJD and chronic wasting disease in the next few months based on the spiralplasma bacteria. If his theory is correct, and the test works, he said it would go a long way toward detecting those infected and perhaps help elucidate the role prions play in these dangerous diseases.
Steve Mitchell is UPI's Medical Correspondent. E-mail sciencemail@upi.com
Copyright © 2001-2004 United Press International
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