Viruses as potential triggers for Alzheimer’s disease

New studies show correlation between viral infections and Alzheimer’s

The Corona pandemic has also led to a focus on viruses as potential triggers for neurodegenerative diseases. The links between virus exposure and neuroinflammation as well as neurodegeneration are currently under intense investigationRecent research has already pointed to a clear link between an increased risk of multiple sclerosis following a previous Epstein-Barr virus (EBV) infection. Two new studies now provide further insight and show once again the role that viral infections can play in the development of neurodegenerative diseases.

Viruses seem to have more influence on nerve diseases than previously suspected.

In an American study, the influence of viral infections on neurodegenerative diseases emerges clearly from health data on more than 800,000 people. The Centre for Alzheimer’s Disease and Related Dementias (CARD), National Institute on Aging and National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA published its latest data on this in the journal Neuron.

“In light of recent findings linking Epstein-Barr virus to an increased risk of multiple sclerosis, as well as increasing concern about the neurological impact of the coronavirus pandemic, we investigated possible associations between viral exposures and risk of neurodegenerative disease,” said study leader Kristin S. Levine.

To begin their study, the research team used a Finnish database from which they analysed the health data of 300,000 patients. The focus was on Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), dementia, multiple sclerosis, Parkinson’s disease and vascular dementia. The researchers looked for possible links between these diseases and viral infections such as chickenpox, Epstein-Barr, meningitis, hepatitis or influenza.

The analysis revealed a total of 45 correlations among the 300,000 patients, suggesting that some of the people affected had previously experienced the same viral diseases. To support these results, the researchers also analysed 100,000 patients’ data from a British database and found 22 further correlations.

Viral encephalitis and Alzheimer’s dementia most frequently associated

The time span between a viral illness and the onset of a neurodegenerative disease varied between one and 15 years. For some diseases, the researchers found significantly more frequent associations with specific viruses. “The strongest association was between exposure to viral encephalitis and Alzheimer’s disease. Influenza with pneumonia was significantly associated with five of the six neurodegenerative diseases studied,” the researchers said. “We were also able to confirm the association between Epstein-Barr and multiple sclerosis with our data.”

Despite their findings, the scientists are aware that this alone is not proof that viruses can trigger the degenerative diseases. It is also conceivable, for example, that they have found a reversal of their thesis. People suffering from one of these diseases could have an increased susceptibility to viral diseases. This has already been shown in animal experiments, as the researchers explain: “We already know this from animal models and were able to observe this increasingly in Alzheimer’s patients in the Corona pandemic.”

Undeniable link between viruses and severe diseases

Nevertheless, there is an undeniable link between the viruses studied and the severe diseases, he said. Further investigations and studies will be needed to determine whether the viruses are indeed the triggers or whether there is a previously unrecognised link, the American research team concludes.

University of Freiburg: Viral infections can trigger Alzheimer’s decades later

Whether and to what extent viral infections in younger years of life play a role in the later development of Alzheimer’s dementia was the subject of a new study by the University of Freiburg. In a study with mice, the scientists showed a connection between inflammation and Alzheimer’s disease. The researchers suspect that these results can also be transferred to humans, as the University of Freiburg reports in a press release. “This could be, for example, chronic inflammations such as chlamydia, which appear at the age of 35,” the head of the research group, Lavinia Alberi Auber, explained to the Keystone-SDA news agency.

To investigate the connection, the researchers developed a new mouse model that uses a special polymer called PolyI:C. This molecule acts as a kind of barrier between the two. This molecule acts as a kind of pseudo-virus and triggers a reaction in the organism similar to that of a viral infection.

The mice were injected with PolyI:C twice, once before birth during the mother’s pregnancy and a second time in adulthood. The scientists then studied the effects of the inflammatory response on the mice’s brains throughout their lifespan.

Until now, the researchers’ focus had been predominantly on infections later in life. “We were able to demonstrate for the first time that chronic inflammation that develops early in life due to a viral pathogen has a decisive influence on changes in the brain in old age,” said Alberi Auber. The results have now been published in the scientific journal “Brain, Behavior, & Immunity”.