Herpes Virus May Be Behind Alzheimer's Progression

Could a Very Common Virus Accelerate Alzheimer's? A new study has found that a herpesvirus infection increased memory loss and brain damage in animals, and showed that antiviral treatment was able to reverse some of these effects. The discovery may open new avenues for combating the disease.

Alzheimer's disease is the leading cause of dementia worldwide, affecting millions of people and causing a gradual loss of memory, reasoning, and autonomy. While genetics is a major risk factor, it does not explain all cases of the disease.

For many years, scientists have been investigating whether common infections could also contribute to the development or accelerate the progression of Alzheimer's. Among the main suspects are herpesviruses, a group of viruses that are extremely common in the population and remain in the body for life after the initial infection.

To investigate this hypothesis, researchers used genetically modified mice to develop alterations very similar to those observed in Alzheimer's disease in humans. These animals were infected with a version of cytomegalovirus, a herpesvirus that, as in humans, remains in the body for life.

Throughout the study, scientists monitored the memory, behavior, and brain changes of these animals, comparing them with mice that had not been infected.

In addition to assessing learning and memory capacity, the researchers analyzed brain tissue in detail. They observed the accumulation of the tau protein, whose alteration is directly related to the death of neurons in Alzheimer's, assessed the loss of connections between nerve cells, and identified which immune system cells migrated to the brain during infection. They also tested whether eliminating these defense cells or using an antiviral drug would be able to reduce the observed damage.

The results were striking. Infected animals developed memory loss more rapidly and showed an increase in altered tau protein, greater loss of connections between neurons, and an intense influx of immune cells, especially a type called CD8 T lymphocytes, into the brain. Instead of just fighting the virus, these cells seemed to contribute to an inflammatory environment that accelerated brain degeneration.

To confirm this hypothesis, the researchers conducted further experiments. When they reduced the number of these immune cells or treated the animals with an antiviral drug during the chronic phase of the infection, brain inflammation decreased and performance on memory tests improved significantly.

This suggests that it is not only the virus itself that may be involved, but also the exaggerated response of the immune system over time.

It is important to note that this study was conducted on animals and does not mean that every person infected with herpes will develop Alzheimer's. In fact, the vast majority of the population comes into contact with some herpesvirus during their lifetime and never develops dementia.

However, the results offer an important clue as to how chronic viral infections can accelerate the disease in people who already have a genetic predisposition or other risk factors.

If future research confirms these findings in humans, new strategies may emerge to prevent or slow the progression of Alzheimer's. In addition to treatments targeting beta-amyloid and tau proteins, currently being studied, antiviral drugs and therapies capable of controlling the immune system's response could become important allies in the fight against the disease.

The study reinforces an idea that is increasingly present in neuroscience: brain health also depends on how our body responds to infections throughout life.

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Cytomegalovirus-induced T cell responses accelerate Alzheimer’s disease progression in mice

Morgan Marsden, James E McLaren, Ryan J Bevan, Daisy Penn-Ripley, Michelle Somerville, Sarah N Lauder, Manon H Jones, Lila-Blythe Maros, Matthew R McGurk, Awen Gallimore, David A Price, Kelly L Miners, Kristin Ladell, Florian A Siebzehnrubl, Timothy R Hughes, Ian R Humphreys, and Mathew Clement

Brain. awag043. 13 July 2026DOI: 10.1093/brain/awag043

Abstract: 

Infections have long been implicated as causative factors in Alzheimer’s disease (AD). Multiple studies have further suggested a key role for herpesviruses, such as cytomegalovirus (CMV). Using transgenic 3xTg-AD mice, we demonstrate that systemic infection with the β-herpesvirus murine CMV (MCMV) accelerates the development of cognitive decline, tauopathy and synaptic loss in the hippocampus, all of which are key features of AD. Accelerated disease progression after infection was associated with substantial lymphocyte infiltration into the brain, dominated by MCMV-specific effector memory CD8+ T cells expressing CXCR3. T cell receptor analyses revealed that clonally diverse virus-specific CD8+ T cells were selectively recruited into the brain during the development of AD. T cell depletion or treatment with the antiviral drug valganciclovir during chronic infection reduced lymphocytic infiltrates in the brain and reversed cognitive decline. These data provide a mechanistic link between chronic viral infections and the development of AD.