Herpes linked to half of Alzheimer's cases, leading scientist says

The herpes virus is linked to half of all Alzheimer’s cases, according to new research.

Leading expert Professor Ruth Itzhaki said recent studies in Taiwan found antiviral drugs drastically reduced the risk of dementia in patients with severe herpes infections.

This followed a lifetime of evidence that the virus - best known for its role in cold sores - fuels rogue amyloid beta proteins that destroy neurons.

Prof Itzhaki's review published in Frontiers in Ageing Neuroscience raises the distant prospect of a simple, effective preventive treatment for one of the most prevalent serious diseases.

Herpes viruses remain for life in our neurons and immune cells, reactivating and resurfacing in characteristic blisters when we are run down by stress or illness.

Most people are infected by the cold sore virus HSV1 (Herpes Simplex Virus 1) by the time they reach old age. It could be behind more than half of Alzheimer's cases.

It is a different strain from the HSV2 virus that causes genital sores.

Professor Itzhaki, of the University of Manchester, said: "HSV1 could account for 50 per cent or more of Alzheimer's disease cases."

She has spent over 25 years investigating the potential link.

Her previous work has shown cold sores occur more frequently in carriers of a gene mutation called APOE-ε4 that increases the risk of Alzheimer's.

Prof Itzhaki said: "Our theory is that in APOE-ε4 carriers, reactivation is more frequent or more harmful in HSV1-infected brain cells, which as a result accumulate damage that culminates in development of Alzheimer's."

But few countries collect the population data required to test whether antiviral treatments reduce dementia risk.

In Taiwan, however, researchers have done just that.

There, 99.9 per cent of the population is enrolled in a National Health Insurance Research Database, which is being extensively mined for information on microbial infections and disease.

In 2017-2018 three such studies were published comparing the development of dementia - of which Alzheimer's is the main cause - and the treatment of patients with HSV or the chickenpox virus VZV (varicella zoster virus).

Prof Itzhaki said: "The striking results include evidence that the risk of senile dementia is much greater in those who are infected with HSV, and that anti-herpes antiviral treatment causes a dramatic decrease in number of those subjects severely affected by HSV1 who later develop dementia."

Her own researchers have found HSV1 causes protein deposits characteristic of Alzheimer's - 'plaques' between neurons and 'tangles' inside them.

She said: "Viral DNA is located very specifically within plaques in postmortem brain tissue from Alzheimer's sufferers.

"The main proteins of both plaques and tangles accumulate also in HSV1-infected cell cultures - and antiviral drugs can prevent this."