Two common herpes viruses appear to play a role in Alzheimer’s disease.
The viruses, best known for causing a distinctive skin rash in young children, are abundant in brain tissue from people with Alzheimer’s, a team of scientists reports Thursday in Neuron. The team also found evidence that the viruses can interact with brain cells in ways that could accelerate the disease.
“Our hypothesis is that they put gas on the flame,” says Joel Dudley, an author of the study and an associate professor of genetics and genomic sciences at the Icahn School of Medicine at Mt. Sinai in New York City.
The finding adds credence to a decades-old idea that an infection can cause Alzheimer’s disease. It also suggests that it may be possible to prevent or slow Alzheimer’s using antiviral drugs, or drugs that modulate how immune cells in the brain respond to an infection.
But the study doesn’t prove that herpes viruses are involved in Alzheimer’s, says Dr. Richard Hodes, director of the National Institute on Aging, which helped fund the research.
“The data are very provocative, but fall short of showing a direct causal role,” he says. “And if viral infections are playing a part, they are not the sole actor.”
Even so, the study offers strong evidence that viral infections can influence the course of Alzheimer’s, Hodes says.
Like a lot of scientific discoveries, this one was an accident. “Viruses were the last thing we were looking for,” Dudley says.
He and a team of researchers were using genetic data to look for differences between healthy brain tissue and brain tissue from people who died with Alzheimer’s.
The goal was to identify new targets for drugs. Instead, the team kept finding hints that brain tissue from Alzheimer’s patients contained higher levels of viruses.
“When we started analyzing the differences, it just sort of came screaming out at us from the data,” Dudley says.
The team found that levels of two human herpes viruses, HHV-6 and HHV-7, were up to twice as high in brain tissue from people with Alzheimer’s. They confirmed the finding by analyzing data from a consortium of brain banks.