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Half of Alzheimer’s cases may be caused by the herpes virus

Half of all Alzheimer’s cases may be caused by the herpes virus that is responsible for cold sores, a scientist has claimed.

Sufferers of the memory-robbing disorder are much more likely to be infected with the Herpes Simplex Virus type 1 (HSV1), a study found.

Professor Ruth Itzhaki, of Manchester University, claims the virus causes similar protein deposits in the brain to the characteristic plaques of Alzheimer’s.

The World Health Organization estimates that two thirds of people under 50 are infected with HSV-1, which causes cold sores.

Once infected with HSV-1, it remains in a sufferer’s nerve and immune cells for life, and can reactivate to cause painful blisters when they are run down or stressed. 

Half of Alzheimer’s cases may be caused by the herpes virus behind cold sores (stock)

Although most people are infected with HSV-1 by the time they reach old age, those who are also genetically at risk of Alzheimer’s may see the virus reactive more frequently or aggressively.

Over time, this could lead to brain damage and eventual cognitive decline. 

The discovery may lead to Alzheimer’s being treated with existing herpes drugs, according to study author Professor Itzhaki, who has spent more than 25 years investigating the potential link.

Most countries, including the UK, do not collect data that draws a link between herpes and Alzheimer’s. However, Taiwan is an exception.

Some 99.9 per cent of the population is enrolled in a National Health Insurance Research Database that collects information on infections and diseases.

Between 2017 and 2018, three studies used this data to analyse a possible link between senile dementia and infection with the herpes or chickenpox virus. 

Senile dementia is mental deterioration associated with ageing – Alzheimer’s is the main cause.

‘The striking results include evidence that the risk of senile dementia is much greater in those who are infected with HSV,’ Professor Itzhaki said.

‘HSV-1 could account for 50 per cent or more of Alzheimer’s disease cases.’

The study also found taking antiviral herpes drugs dramatically reduce the number of people infected with the virus who go on to develop Alzheimer’s. 

The findings were published in the journal Frontiers in Ageing Neuroscience.

Professor Itzhaki stresses, however, the participants in the three studies were suffering from severe herpes infections, which are rare.

‘Ideally, we would study dementia rates among people who have suffered mild HSV-1 infection, including herpes labialis (cold sores) or mild genital herpes, but these are far less likely to be documented,’ she said.

Although further research is required, Professor Itzhaki is optimistic herpes treatments could be used to ease dementia.

‘Considering that over 150 publications strongly support an HSV-1 role in Alzheimer’s, these Taiwan findings greatly justify usage of antiherpes antivirals – which are safe and well-tolerated – to treat Alzheimer’s disease,’ she said.

‘They also incentivize [the] development of an HSV-1 vaccine, which would likely be the most effective treatment.’

An HPV vaccination is already used worldwide to prevent cervical cancer, which is another example of a virus causing a disease. 


Herpes viruses cause cold sores, which most commonly appear on the lips or genitals.

Around seven in 10 people in the UK are infected with the viruses.

However, only around one in three experience symptoms. 

In the US, around half of young adults are infected with the virus that causes cold sores around the mouth.

One in eight have the virus behind genital herpes.  

Cold sores on the lips most commonly get passed on by being kissed by someone with an active cold sore. 

They begin as a small red patch that blisters before bursting, leaving a raw area that scabs. 

Cold sores that appear on the face are most commonly caused by the herpes simplex type 1 virus.

Type 2 mainly affects the genitals.

It is rare for cold sores to spread away from the site they first appeared in.

And they are only transmitted by direct skin contact, not by sharing items such as towels or cutlery.

Oral sex is a common way for cold sores to pass from a person’s mouth to another’s genitals or vice versa.  

Once infected, sufferers may initially experience a fever and flu-like symptoms.

Cold sores can reappear if triggered by stress, illness, alcohol or too much sunlight.

This is because the virus stays in a nerve junction near the spinal cord. 

Many feel an itch, tingle or shooting pain before a cold sore reappears.

Antiviral medication may be prescribed if someone frequently suffers from outbreaks. 

Keeping sores moisturised can stop them cracking and becoming painful. 

Source: Herpes Viruses Association 

Although the study seems positive, other experts question how encouraging the results actually are. 

‘This review article discusses previous research linking the herpes viruses to Alzheimer’s and as such, adds no new evidence to support a link between the two,’ Dr David Reynold, of Alzheimer’s Research UK, said.

‘This review presents mainly correlative studies that do not give clear evidence of cause and effect. 

‘The evidence presented in this review is not sufficient to suggest that Alzheimer’s is contagious and be passed from person-to-person like a virus and neither does it mean that having cold sores increases your risk of getting dementia.

‘A growing body of evidence is linking the immune system with Alzheimer’s, and it’s important to explore the role that inflammation might play in the development and progression of the disease.’

Dr James Pickett, head of research at Alzheimer’s Society, added: ‘Herpes is a hot topic in dementia research, as the infection appears to be more common in the brains of people with Alzheimer’s compared to healthy brains.

‘But we don’t yet know enough about the relationship between the two.

‘The link between herpes and dementia isn’t something that we feel people should worry about, although it’s sensible general advice to seek treatment for persistent cold sores. 

‘Dementia is not contagious and shouldn’t be thought of as an infectious disease.’

Around seven in 10 people in the UK are infected with a herpes virus, which can also cause genital sores.

However, many are unaware they carry the infection due to symptoms only appearing in one in three people.

In the US, around half of young adults are infected with the virus that can cause cold sores around the mouth.

And one in eight carry the virus that usually leads to genital herpes.

This comes after research released earlier this week found women who have pre-eclampsia during pregnancy are three-and-a-half times more likely to get dementia in later life.

Those who develop the potentially fatal complication while expecting are at greater risk of vascular dementia, caused by reduced blood flow to the brain, according to researchers from the Statens Serum Institut, Copenhagen.


Alzheimer’s disease is a progressive, degenerative disease of the brain, in which build-up of abnormal proteins causes nerve cells to die.

This disrupts the transmitters that carry messages, and causes the brain to shrink. 

More than 5 million people suffer from the disease in the US, where it is the 6th leading cause of death.


As brain cells die, the functions they provide are lost. 

That includes memory, orientation and the ability to think and reason. 

The progress of the disease is slow and gradual. 

On average, patients live five to seven years after diagnosis, but some may live for ten to 15 years.


  • Loss of short-term memory
  • Disorientation
  • Behavioral changes
  • Mood swings
  • Difficulties dealing with money or making a phone call 


  • Severe memory loss, forgetting close family members, familiar objects or places
  • Becoming anxious and frustrated over inability to make sense of the world, leading to aggressive behavior 
  • Eventually lose ability to walk
  • May have problems eating 
  • The majority will eventually need 24-hour care   

 Source: Alzheimer’s Association


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