You probably know herpes, or HSV1, as the cause of a cold sore, a common virus that affects two out of three people under the age of 50. Now, an expert says that it could also be the leading cause of Alzheimer’s disease.
“HSV1 could account for 50 percent or more of Alzheimer’s disease cases,” said Ruth Itzhaki, professor in the Division of Neuroscience and Experimental Psychology at the University of Manchester, U.K.
Itzhaki’s theory is not a new one. Earlier this year, scientists announced that two types of herpes, HHV-6A and HHV-7, are common in the brains of people with Alzheimer’s. Those two strains of herpes are common in children and cause a rash known as roseola.
We typically think of these types of herpes as harmless—but they remain in our cells and central nervous system for life. And Itzhaki previously found that for those who carry a copy of ApoE4, the gene most associated with Alzheimer’s, herpes pops back up most frequently when compared to those who have another variation of that gene.
“The virus can become active in the brain, perhaps repeatedly, and this probably causes cumulative damage,” wrote Itzhaki in an editorial on The Conversation. “The likelihood of developing Alzheimer’s disease is 12 times greater for APOE4 carriers who have HSV1 in the brain than for those with neither factor.”
Itzhaki’s assessment of herpes as a major player in Alzheimer’s comes after a review of a Taiwanese database that has enrolled 99.9 percent of its residents. They analyzed who was diagnosed with dementia and also had been treated for HSV or chickenpox.
“The striking results include evidence that the risk of senile dementia is much greater in those who are infected with HSV, and that anti-herpes antiviral treatment causes a dramatic decrease in number of those subjects severely affected by HSV1 who later develop dementia,” said Itzhaki.
The good news: If Alzheimer’s has a viral beginning, it could be treated with antiviral drugs. An earlier study conducted by Itzhaki found that the drug acylovir, a drug prescribed to lessen the likelihood of a herpes outbreak, blocks the replication of the HSV1 virus in DNA and reduces beta-amyloid and tau, two toxic proteins that accumulate in Alzheimer’s disease, in the brain.
“Considering that over 150 publications strongly support an HSV1 role in Alzheimer’s, these Taiwan findings greatly justify usage of antiherpes—which are safe and well-tolerated—to treat Alzheimer’s disease,” said Itzhaki.
The study does not prove that herpes causes Alzheimers; but it does show an association between carrying HSV1 and later developing dementia. More studies are need before a strong connection can be established.
“Herpes is a hot topic in dementia research, as the infection appears to be more common in the brains of people with Alzheimer’s compared to healthy brains—but we don’t yet know enough about the relationship between the two,” said James Pickett, Ph.D., Head of Research at the Alzheimer’s Society.
“The link between herpes and dementia isn’t something that we feel people should worry about, although it’s sensible general advice to seek treatment for persistent cold sores,” said Pickett. “Dementia is not contagious and shouldn’t be thought of as an infectious disease.”