New study highlights Alzheimer’s herpes link
A new commentary by scientists at the Universities of Manchester and Edinburgh on a study by Taiwanese epidemiologists supports the viability of a potential way to reduce the risk of Alzheimer’s disease.
When the Taiwanese authors looked at subjects who suffered severe herpes infection and who were treated aggressively with antiviral drugs, the relative risk of dementia was reduced by a factor of 10.
Manchester’s Professor Ruth Itzhaki and Edinburgh’s Professor Richard Lathe say the paper, by Tzeng et al. and published in Neurotherapeutics in February 2018, also shows that herpes simplex virus type 1 (HSV1) leads to an increased risk of developing the disease.
“This article and two others by different research groups in Taiwan provide the first population evidence for a causal link between herpes virus infection and Alzheimer’s disease, a hugely important finding,” said Professor Itzhaki.
Professor Itzhaki said, ”Successful treatment by a specific drug, or successful vaccination against the putative microbe, are the only ways to prove that a microbe is the cause of a non- infectious human disease.”
Most Alzheimer’s disease researchers investigate its main characteristics – amyloid plaques and neurofibrillary tangles; however, despite the vast amount of research, the causes of their formation are unknown.
HSV1 infects most humans in youth or later and remains lifelong in the body in dormant form within the peripheral nervous system. From time to time the virus becomes activated and in some people it then causes visible damage in the form of cold sores.
The Taiwanese study identified 8,362 subjects aged 50 or more during the period January to December 2000 who were newly diagnosed with severe HSV infection. The study group was compared to a control group of 25,086 people with no evidence of HSV infection.
The authors then monitored the development of dementia in these individuals over a follow-up period of 10 years between 2001 and 2010.
The risk of developing dementia in the HSV group was increased by a factor of 2.542. But, when the authors compared those among the HSV cohort who were treated with antiviral therapy versus those who did not receive it, there was a dramatic tenfold reduction in the later incidence of dementia over 10 years.
Professor Richard Lathe added: “Not only is the magnitude of the antiviral effect remarkable, but also the fact that—despite the relatively brief duration and the timing of treatment—in most patients severely affected by HSV1 it appeared to prevent the long-term damage in brain that results in Alzheimer’s.
Professor Itzhaki said, “So we believe the cycle of HSV1 reactivation in the brain eventually causes Alzheimer’s in at least some patients.”
The study by Tzeng et al. investigated only people with severe HSV and cannot be generalised to healthy populations.
The paper: ‘Herpes Viruses and Senile Dementia: First Population Evidence for a Causal Link’ is published in the Journal of Alzheimer's Disease.
18 July 2018.