The numbers are daunting. Approximately 5.7 million Americans live with Alzheimer's disease. It's also estimated that nearly one-half of people worldwide have herpes simplex virus type 1 (HSV-1), the usual cause of oral herpes, and more often now, genital herpes. And it's likely that one in eight people ages 14 – 49 in the United States has genital herpes caused by herpes simplex virus type 2 (HSV-2).
Maybe you have one of these conditions, or know someone who does.
Alzheimer's and herpes may seem like unlikely partners, but they may have more in common than scientists once thought. The decidedly unglamorous herpesvirus, specifically human herpesvirus strains HHV-6A and HHV-7, may be involved in the development and progression of Alzheimer's, says a 2018 study published in the journal Neuron. Note: These two herpes viruses aren't sexually transmitted, while HSV-1 and HSV-2 are. There are actually nine types of herpesvirus that can infect humans.
But don't stay up late worrying that you will be immediately impacted by these findings, experts advise. Here's what you need to understand about this study and others linking Alzheimer’s and herpes.
What the research says about herpes and Alzheimer’s
In the study, the 15 researchers analyzed data from 622 postmortem — from a dead body — brains of people who once exhibited symptoms of Alzheimer's, along with brains of people seemingly untouched by this devastating disease. They found nearly two times the level of herpesvirus, HHV-6A and HHV-7, in the Alzheimer's brains when compared with the "normal" brains. The findings were replicated in two additional independent cohorts, or groups of people, the researchers said.
It's important to note that because the researchers found viruses in both Alzheimer's and non-Alzheimer's brains, we can't assume that herpes infections alone caused the devastating brain disease to develop.
According to a news release, researchers from the Icahn School of Medicine at Mount Sinai "identified previously unknown gene networks that will both offer new testable hypotheses for understanding Alzheimer’s pathology and reveal novel potential targets for new drugs that may arrest Alzheimer's disease progression, and could potentially prevent the disease if administered early enough."
‘Association,’ not ‘cause’: What does this mean?
"The link between herpesvirus and other microbes has been studied for a number of years but hasn't really been part of mainstream research in Alzheimer's disease," said Keith Fargo, Ph.D., director of scientific programs and outreach for the Alzheimer's Association, in a telephone interview with HealthCentral.
"This paper from a world-class group of authors is going to move this hypothesis into the mainstream," he says.
What causes Alzheimer's remains a very open question, Dr. Fargo says.
"Some infectious organism might play a role in that,” he says. “The paper doesn't establish herpes or any other microbe as a causative agent [the biological pathogen that causes a disease] but opens the door to more research to shed future light on this."
Everyone probably has some level of worry about Alzheimer's, since one out of three people 85 and older has the disease, he says.
"I wouldn't worry specifically because a person had the herpesvirus because it's exceedingly common,” Dr. Fargo says. “The viruses we're talking about here are HHV-6 and -7, which most children have and carry with them the rest of their lives. As children, [these two herpes types] cause the illness roseola, and as people get into old age, more than 90 percent have these viruses."
He reiterated that the latest paper does not show a causative link but that it shows an association. Again, that means the paper doesn't prove that those two herpesviruses definitively cause Alzheimer's, so none of us should panic.
The strengthening link between viruses and Alzheimer’s
The 2018 study isn’t the first to discuss a potential link between Alzheimer’s and infections like herpes.
In 2016, the Journal of Alzheimer's Disease published an editorial from a respected international group of 33 scientists who wrote that they were concerned “one particular aspect of the disease has been neglected, even though treatment based on it might slow or arrest [Alzheimer’s disease] progression. We refer to the many studies, mainly on humans, implicating specific microbes in the elderly brain, notably herpes simplex virus type 1 (HSV1)…"
One of these experts, Timo Strandberg, M.D., Ph.D., of the University of Helsinki (Finland), had previously written an editorial in Neurology in 2013, questioning the role of infections with disorders that cause dementia.
Another, Ruth Itzhaki, Ph.D., also authored a comment in the Alzheimer's journal in 2018, citing three articles that "provide the first population evidence for a causal link between herpesvirus infection and senile dementia (mental deterioration in old age)."
One article does deal with HSV-1 (again, the type that most often causes oral herpes) and says that aggressive treatment with antiherpetic medications — meaning those that fight herpes — reduced relative risk of senile dementia by a factor of 10.
In an email to HealthCentral, Dr. Strandberg writes that in fact, recent developments have been strengthening the virus association with Alzheimer’s, and not only with herpes simplex viruses.
"I still think that dementing disorders are multifactorial, so simply being herpes positive doesn't give you Alzheimer's," Dr. Strandberg says. "[It is] a very intriguing and important topic, though, which needs more research."
A new Alzheimer’s drug on the horizon?
In related and encouraging news, at the Alzheimer's Association International Conference in July 2018, Eisai Co., Ltd. and Biogen Inc. announced additional results of a clinical trial of an experimental Alzheimer’s drug called BAN2401.
Here's the interesting part: There is a beta-amyloid protein involved in Alzheimer's and considered especially toxic that builds up and "clumps" together to create plaques between the brain's neurons and then disrupts normal function of brain cells. In the BAN2401 trial, researchers found that the drug helped reduce these amyloid plaques and improved cognition and function — definitely news worth noting along the long, long road to an Alzheimer's cure.
While the association noted that "the studies were not large enough to definitely demonstrate cognitive efficacy and the BAN2401 study did not meet its primary endpoint," the results are still a step forward in understanding and treating the disease.
What this research means for you
As the experts here have said, a herpes diagnosis doesn't mean you definitely have Alzheimer's or will have it someday. Yet, the buzz around the studies noted here offers hope to people with Alzheimer's and their loved ones, friends, and advocates, many of whom say more funding is needed than the $1.9 billion allocated for research in 2019.
It’s also critically important for everyone to consider participation in a clinical trial for Alzheimer's prevention, says Dr. Fargo. For example, you can use the website TrialMatch to find clinical trials in your area, for people with dementia or Alzheimer's and also for healthy volunteers.
Remember: If you have a form of the herpesvirus, or think you might, maintain an open dialogue and work with your doctor to determine the best ways to treat and control the virus for your unique, personal situation.