Researchers Find Possible
Infectious Bacterial Cause
Of Alzheimer's
By Jane E. Allen
AP Science Writer

LOS ANGELES (AP) -- A bacterium found unexpectedly in the brains of Alzheimer's patients could mean that the dementia-producing disorder has an infectious basis.
Scientists who examined brain tissue of Alzheimer's patients after autopsy found that a bacterium called Chlamydia pneumoniae had invaded brain cells in regions where Alzheimer's damage can be detected.
Researchers were surprised to find the presence of the bacterium because it had penetrated the protective blood-brain barrier, traveling far beyond its common entry point into the body, the sinuses and lungs.
The finding is important to "our potential understanding of how an infectious agent could lead to the neurodegeneration observed in Alzheimer's disease," according to Brian J. Balin, a researcher at Allegheny University of the Health Sciences in Philadelphia.
Balin and a team of colleagues found DNA segments from the bacterium in post-mortem brain samples of 17 of the 19 Alzheimer's patients he analyzed. Conversely, 18 of 19 brain samples from people without Alzheimer's showed no signs of the organism.
"At this time, we do not know if the presence of this organism is causative or if it is a risk factor for the disease," Balin wrote. "However, we believe that our findings support those of others suggesting that inflammation, which can be stimulated by this bacterial infection, is a very important aspect of late-onset Alzheimer's disease."
When cells become infected with the bacterium, they make chemicals to fend off the infection. Those inflammatory chemicals, called cytokines, can damage surrounding nerve cells.
"The damage may cause changes in an individual's ability to recall information such as people and places and the ability to think coherently -- common clinical features which are seen in Alzheimer's disease," Balin wrote.
A top Alzheimer's expert said Balin's report -- which was presented Wednesday at the annual meeting of the Society for Neuroscience -- was a "provocative, exciting finding."
"I think that it's something that's really worth taking seriously because of the issue of what's triggering the degeneration process," said Zaven Khachaturian, a consultant to the Alzheimer's Association.
Khachaturian said the critical question is to identify the trigger, which he suggested might be some sort of trauma or other incident that creates damage to the blood-brain barrier and lets the bacteria in.
"Now you have a break in the pipe all of a sudden setting the stage for other events to occur," Khachaturian said. "I think this is a likely scenario."
Khachaturian said it's also important to find out whether the bacteria has set the stage for Alzheimer's in the patients who died, or whether the Alzheimer's damaged the brain, letting in the bacteria.
Cells infected by the bacterium make chemicals to fend off the infection. Those inflammatory chemicals, called cytokines, can in turn damage surrounding nerve cells.
The same bacterium has been detected in the fatty plaques that clog heart arteries, though researchers do not yet know if it is responsible for the clogging.
Researchers have also found a correlation between late-onset Alzheimer's and infection with herpes simplex virus type 1.