Common virus tied to Alzheimer's: study

Contracting a common virus may play a role in the development of Alzheimer's disease, a new study has found.
The study of the brains of older adults found an association between patients' immune responses to cytomegalovirus (CMV) and signs of Alzheimer's disease.
"More studies are still needed to understand how an active CMV infection might be related to this most common form of dementia," said study researcher Dr Julie Schneider, of the Rush University Alzheimer's Disease Center in Chicago.
The study did not show a cause-and-effect link between CMV and Alzheimer's, LiveScience reported.
It is possible that other stimulants of inflammation, including other viral infections, might also lead to the brain changes seen in the study, which could cause a decline in cognitive function leading to Alzheimer's disease, researchers said.

CMV is transmitted through contact with bodily fluids, including sexual contact.

In the new study, Schneider and her colleagues analysed blood and cerebrospinal fluid (brain- and spinal-cord fluid) samples from the bodies of people who were part of an ageing-and-dementia study during their lives.
All had passed away, and had mild or probable Alzheimer's disease at the time of their death. Of the participants, 37 had antibodies against CMV, and 22 were CMV-negative.
The researchers found that 80 per cent of the patients who were positive for a CMV infection had high levels of an inflammation marker in their cerebrospinal fluid, while none of the patients who were negative for the virus had this marker present.

Such a clear-cut difference supports the idea that CMV may specifically cause inflammation related to Alzheimer's, said study researcher Nell Lurain, professor of immunology at Rush University.
The patients with higher levels of antibodies against CMV were also more likely to have brain cells with aggregated tau proteins, called neurofibrillary tangles that have been connected to Alzheimer's disease.
The herpes simplex virus (HSV1), another virus that can infect the brain and spinal cord, has also been linked with Alzheimer's progression. But the new study did not find a connection between HSV1 and markers of Alzheimer's disease in patient samples.
The study also showed no evidence of a link between higher levels of CMV infection and levels of amyloid-beta - an imperfect marker of Alzheimer's but still the hallmark of the disease that most researchers consider the best indicator.

However, researchers did see that infecting human cells in lab dishes with CMV, but not HSV1, resulted in an increase in amyloid-beta protein.