Researchers have found a "striking correlation" between herpes and Alzheimer's, raising hopes a vaccine for the latter could be on the horizon.
Herpes simplex virus 1 (HSV-1) is highly contagious, infections are life-long and most people will have it by the time they're an adult. It's best-known for causing cold sores, but a new study has found it could also be behind at least half of all Alzheimer's cases.
The link is a gene called APOE-ε4.
"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," says Prof Ruth Itzhaki of the University of Manchester.
Her team looked at data from Taiwan, which unlike most countries has detailed health data on virtually every one of its citizens. They found a strong link between people with senile dementia caused by Alzheimer's, and treatment for HSV-1 or chickenpox infections (caused by the varicella zoster virus, a form of herpes).
"The striking results include evidence that the risk of senile dementia is much greater in those who are infected with HSV-1, and that anti-herpes antiviral treatment causes a dramatic decrease in number of those subjects severely affected by HSV-1 who later develop dementia."
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Prof Itzhaki's previous research has found HSV-1 creates protein deposits on the brain in a similar way to Alzheimer's.
She says the Taiwanese data is limited in that it only records severe cases of HSV-1 infections.
"Ideally, we would study dementia rates amongst people who have suffered mild HSV1 infection, including herpes labialis (cold sores) or mild genital herpes, but these are far less likely to be documented."
But she still thinks it's strong evidence we might one day have a way to prevent the onset of Alzheimer's, which affects around 70,000 New Zealanders. Alzheimer's NZ estimates with our growing elderly population, more than 170,000 will be living with it by 2050, costing the country about $5 billion in healthcare costs.
"Considering that over 150 publications strongly support an HSV1 role in Alzheimer's, these Taiwan findings greatly justify usage of antiherpes antivirals - which are safe and well-tolerated - to treat Alzheimer's disease," says Prof Itzhaki.
"They also incentivise development of an HSV1 vaccine, which would likely be the most effective treatment."
The research was published in journal Frontiers in Aging Neuroscience.