(CNN) Doctors don't know what causes Alzheimer's disease or the best way to treat it, but they have new evidence to suggest that a common virus may play a role in who develops the condition.
In a study published Thursday in the journal Neuron, researchers say they've found strong evidence to suggest that two strains of the human herpes virus -- 6A and 7 -- may contribute to the disease that robs people of their memory and cognitive functions.
Someone in the United States develops Alzheimer's every 65 seconds, and by midcentury, it's expected to be every 33 seconds, according to the Alzheimer's Association. With costs of care running into the trillions of dollars by that time, scientists are working urgently to understand the disease in hopes of finding a cure or at least an effective treatment. Alzheimer's is the sole disease in the top 10 US causes of death that has no significant treatment available.
The researchers in the new study looked at data on 622 brains from people who had had signs of the disease and 322 from people who did not seem to be affected by it. The brains with Alzheimer's had levels of the herpes virus that were up to twice as high as in people who did not have the disease.
Some scientists have long believed that viruses play a role in the development of Alzheimer's. One of the most prominent theories is that Alzheimer's may start in the brain as a response to injury from a virus. Another theory is that Alzheimer's is a mix of disease process in the brain, but experts don't know for sure.
"I don't think we can answer whether herpes viruses are a primary cause of Alzheimer's disease. But what's clear is that they're perturbing networks and participating in networks that directly accelerate the brain towards the Alzheimer's topology," Joel Dudley, a geneticist and co-author on the study, said in a statement. Dudley is a member of the ASU-Banner Neurodegenerative Disease Research Center.
The researchers were surprised by the results of the study, he said. "The title of the talk that I usually give is, 'I Went Looking for Drug Targets, and All I found Were These Lousy Viruses,' " he said.
Dudley believes the new study could help scientists identify virus biomarkers in the brain that could one day help diagnose the disease and assess a person's risk. He also hopes it could be the beginning of research that would provide new targets in the brain for drugs to treat the condition.
"This is the most compelling evidence ever presented that points to a viral contribution to the cause or progression of Alzheimer's," said study co-author Dr. Sam Gandy, a professor of neurology and psychiatry and director of the Center for Cognitive Health at Mount Sinai in New York.
The scientists caution that people shouldn't be alarmed by their discovery. This particular set of herpes viruses is common. About 90% of adults have been exposed to the herpes virus by age 50, research shows, and not all of them will go on to develop dementia.
"While these findings do potentially open the door for new treatment options to explore in a disease where we've had hundreds of failed trials, they don't change anything that we know about the risk and susceptibility of Alzheimer's disease or our ability to treat it today," Gandy said.
Keith Fargo, the Alzheimer's Association's director of scientific programs and outreach, said that more research will need to be done to prove that there is a connection between herpes viruses and Alzheimer's.
"However, if viruses or other infections are confirmed to have roles in Alzheimer's, it may enable researchers to find new antiviral or immune therapies to treat or prevent the disease," Fargo said. "The Alzheimer's Association welcomes new ideas in the Alzheimer's field and new avenues to pursue for potential treatments and prevention strategies."