Strandberg said he thinks only a controlled clinical trial can give answers. He said a first step could be a trial where Alzheimer's patients are randomly assigned to take an antiviral drug to prevent reactivation of herpes viruses.
But Katan said any intervention would presumably have to happen earlier. "If they already have dementia, it's too late. The damage would be done," she said.
If further studies do confirm that certain viruses play a role in mental decline, prevention would be important. Katan pointed to vaccines as a potential way to protect people, "but we're a long way off from that," she said.
The study was funded by U.S. and Swiss government grants. Some researchers on the work and Strandberg, the editorialist, have ties to several drug companies.
Learn more about dementia from the U.S. National Institute of Neurological Disorders and Stroke.
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