As evidenced by the prevalence of long COVID, a virus can have lasting effects on the human body. These effects can begin long past the initial viral incubation period, and the symptoms can prove surprising. In a recent study at the Dartmouth College Geisel School of Medicine, researchers used cognitive tests to assess a potential long-term side effect of the herpes simplex virus, or HSV: cognitive changes that are alarmingly similar to those seen in Alzheimer’s disease (AD).
What Is HSV?
The herpes simplex viruses, or HSV, are categorized into two types: herpes type 1 (HSV-1, or oral herpes) and herpes type 2 (HSV-2, or genital herpes). HSV-1 typically causes sores around the mouth, otherwise known as cold sores or fever blisters. Individuals infected with HSV-2 usually have sores below the waist. HSV is incredibly common; the World Health Organization (WHO) estimates that close to 67 percent of the world’s population have HSV-1, while about 11 percent have HSV-2.
Abigail Dutton, a Dartmouth University MD and Ph.D. candidate, led the Geisel School study into potential long-term implications of HSV. “It is likely that over two-thirds of us are infected with HSV right now,” Dutton told Medical XPress. “It has the potential to survive, latent, within our nervous system for decades, traveling not only to the skin, but to the brain.” That last point – HSV’s potential impact on the brain – is key to the Geisel study. Specifically, Dutton sought to test the hypothesis that herpes can impair memory and learning in mice, resembling the pathology of humans with AD.
Using Cognitive Tests to Explore HSV
To explore her hypothesis, Dutton worked with a series of herpes-infected mice using cognitive tests. In one example, the mouse was placed into a box with two identical objects for 10 minutes. The next day, one of the objects was replaced with something different – an object completely unknown to the mouse. Dutton expected that the mouse would be more interested in the new object than the old one. “Exactly the opposite happened,” Dutton told Medical Xpress. “The infected mouse did not show a preference for the new object, suggesting a deficit in its ability to learn and remember ‘novel’ versus ‘familiar.'” Dutton hopes to further explore her hypothesis, eventually applying the findings in a surprising capacity: in pediatrics with expectant mothers.
How HSV Is Transmitted During Birth
Why would Dutton hope to apply lessons learned about HSV to a clinical pediatric setting? “I’m interested how contracting herpes at such an early age might disrupt neural architecture and cause changes in behavior and in the brain, and then consequential neuro-degeneration,” says Dutton. Dutton points out that babies can catch HSV from their mother, especially if the mother is unaware she has the virus. Of course, women who have genital herpes have a very low risk of transmitting the virus to their babies thanks to the presence of antibodies in both the mother and the baby. Transmission does happen, however; HSV-1 can also spread through kissing or touch if the mother has an active cold sore. Either way, Dutton’s research could shed light on potential long-term implications of HSV transmission.
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As Dutton put it, this study sought to explore “the aging end of neurodegeneration and the initial end of contracting a disease.” However, it could also pave the way for further research into the link between viral infection and cognitive changes. That could be key to degenerative disease research endeavors, like those involving AD.
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