Herpesvirus Infection Linked to Accelerated Alzheimer’s Progression

Researchers have identified that herpesvirus infection can exacerbate memory deficits and Alzheimer’s disease-related brain alterations in mice genetically predisposed to the condition. The study indicates that the immune system’s ongoing efforts to control the virus, rather than the virus alone, contribute to this damage.

The investigation provides a potential biological basis for previous research connecting common viral infections with a heightened risk of dementia.

Role of Herpesviruses in Alzheimer’s Disease

Herpesviruses encompass a broad family of viruses responsible for ailments such as cold sores, childhood infections, and glandular fever. After the initial infection resolves, some herpesviruses remain dormant and can reactivate intermittently, repeatedly stimulating the immune system.

Scientists from Cardiff University’s School of Medicine, Systems Immunity Research Institute, and Dementia Research Institute explored whether this persistent immune activation influences Alzheimer’s disease progression. Their findings suggest that T cells, which target infected cells, infiltrate the brain during herpesvirus infection and accelerate cognitive decline.

Dr. Mathew Clement from Cardiff University’s School of Medicine stated, “Infections, including chronic human herpesviruses, which can be associated with cold sores, have long been suspected as increasing the risk of developing Alzheimer’s disease. However, the mechanisms underlying this association have remained largely unknown.”

Experimental Approach to Infection and Immune Response

The research team employed 3xTg-AD mice, genetically modified to develop several Alzheimer’s disease characteristics. These mice were infected with murine cytomegalovirus, a β-herpesvirus model for persistent infection.

Some animals were administered the antiviral drug valganciclovir hydrochloride, while others received antibodies targeting CD4 and CD8 T cells, enabling the researchers to assess the immune response’s role in neurological damage.

Subsequent assessments included tests of memory and cognition, examination of cell loss in the hippocampus, and measurement of amyloid and tau protein accumulation, which are markers of Alzheimer’s disease. The hippocampus is a brain region critical for learning and memory and is affected early in Alzheimer’s pathology.

Immune Cells Invade the Brain During Infection

Post-infection, a substantial influx of immune cells was observed in the brain, predominantly CD8+ T cells specifically recognizing the virus. This indicates their migration as part of the immune system’s effort to contain the infection.

Similar T cells have been detected in the brains and cerebrospinal fluid of Alzheimer’s patients, though their precise function has not been clearly defined.

Antiviral Intervention Enhances Cognitive Outcomes

The study’s key discovery emerged when the immune response was suppressed. Mice treated with antiviral medication or those depleted of white blood cells showed improved performance in cognitive tests.

These results suggest that the immune response driven by the virus actively accelerates Alzheimer’s-like disease progression, rather than merely coexisting with it.

Professor Ian Humphreys, Professor of Viral Pathogenesis and Lead Co-Director of Cardiff University’s Systems Immunity Research Institute, commented, “It remains unclear how virus-induced T cell presence in the brain leads to disease progression, and understanding this may lead to new insights into Alzheimer’s Disease development.”

Implications for Infection Prevention and Dementia Risk

One hypothesis is that immune cells combating persistent infection may cause inflammation that damages nearby neurons or disrupts normal brain defenses. Although the study did not delineate the exact sequence of events, it narrows the focus to interactions among infection, T cells, and vulnerable brain tissue.

Dr. Clement added, “Not only does this research broaden the understanding of the link between herpesviruses and Alzheimer’s disease and further strengthen the link between viruses and dementia more generally, but it raises the importance of prevention of infectious disease and how this, in the long term, may prevent or delay dementia onset.

This study bolsters the argument that dementia risk is not as simple as genetic predisposition, but that environmental factors play an important part. By preventing disease through vaccines, antiviral treatments, and immune support, we can not only be treating and preventing us from getting short-term illnesses—such as cold sores – but those same disease preventions are playing an important role in reducing dementia risk for the later parts of our lives as well.”

The study referenced is “Cytomegalovirus-induced T cell responses accelerate Alzheimer’s disease progression in mice” by Morgan Marsden et al., published 13 July 2026 in Brain (DOI: 10.1093/brain/awag043). The research received support from the Hodge Centre for Neuropsychiatric Immunology, the Medical Research Council, and the Wellcome Trust.