A few studies have already suggested the link between infection with the Herpes simplex virus and an increased risk of Alzheimer's disease. This new research once again begs the question, "But what causes Alzheimer's disease?" ". The answer could be right under our noses, answer the researchers from Taiwan who again invoke the herpes simplex virus type 1 (HSV-1) -responsible for cold sores- as the cause of Alzheimer's disease. And in doing so, they also conclude, in the journal Frontiers in Aging Neuroscience, on the interest, in prevention, of antiviral drugs, which considerably reduce the risk of senile dementia in patients suffering from severe herpes infections.
The main author, Professor Ruth Itzhaki recalls the numerous studies which have already suggested that the herpes virus is responsible for the development of certain types of dementia, including Alzheimer's disease. Herpes viruses remain in our neurons and immune cells for life, reactivating and resurfacing, in some subjects, in the form of characteristic vesicles in the event of stress or great fatigue. And most herpes simplex virus 1 (HSV 1) infections occur in people of advanced age.
Neurons infected with HSV-1 in our brain: what happens to these neurons infected with the herpes virus when it reactivates? The team shows here that in subjects carrying the APOE-ε4 variant, a variant of the gene which increases the risk of Alzheimer's disease, these cold sores linked to HSV 1 are more frequent: "Our theory is that, in carriers of APOE-ε4, reactivation is more frequent or more damaging in brain cells infected with HSV 1, leading to an accumulation of damage favorable to the development of Alzheimer's disease”.
Proof by epidemiology: the team shows, from the analysis of health data from the national register and from the results of 3 recent studies (2017 -2018) that the risk of developing dementia is much higher in people infected with HSV 1 but also that anti-herpes antiviral treatment causes a dramatic reduction in the number of subjects severely affected by HSV 1 who develop dementia.
HSV 1 could thus explain 50% or more of the cases of Alzheimer's disease , estimate the authors. Especially since previous work by the same team has already documented the link that corroborates these epidemiological data: HSV 1 causes deposits of proteins characteristic of Alzheimer's disease, these plaques and inter-neuron tangles. Viral DNA is also found in plaques of postmortem brain tissue from patients with Alzheimer's disease.
If the link with severe cases of Herpes infection is therefore now documented, the researchers wish to look at the effects of milder HSV infections on the risk of dementia much later in life: "Ideally, we would study the rates of dementia in people with mild HSV1 infection, including cold sores or mild genital herpes, cases of dementia that are much less likely to be documented.”
Finally, in the shorter term, data on the efficacy of anti-herpes antiviral treatment in reducing the incidence of dementia in infected subjects are obviously rich in implications.