Alzheimer's and herpes: the dispute continues
Herpes virus is not found to have a connection with Alzheimer's disease
Kirill Stasevich, Science and Life (nkj.ru )
About thirty years ago, a lot of herpes virus DNA was found in brain samples of people with Alzheimer's syndrome – first it was the herpes simplex virus (HSV-1), and then its other varieties, HHV6A and HHV6B. The herpes virus, after it has entered the body, often remains dormant in the cells for a long time, and to meet it in the brain is not such news. However, it turned out to be much more in the brains of patients than in the brains of ordinary people, and since then the herpes virus has been considered as one of the factors in the development of Alzheimer's disease.
Some time ago we wrote about what mechanisms can work here: for example, it turned out that neurons in response to a viral invasion begin to actively synthesize a protein from which toxic molecular deposits characteristic of Alzheimer's disease are formed. The protein suppresses viral infection (and the herpes virus can in some cases provoke encephalitis), but at the same time it can cause other troubles.
However, recently an article by Allnutt et al was published in the journal Neuron. Human Herpesvirus 6 Detection in Alzheimer’s Disease Cases and Controls across Multiple Cohorts. In it, the staff of the National Institute of Neurological Diseases and Stroke express doubt that the herpes virus can even be involved in Alzheimer's disease. The researchers took several hundred brain samples of people with the syndrome and several hundred brain samples of healthy people and looked for traces of viral RNA in them.
The presence of viral RNA would indicate that the virus is more or less active, that it is trying to reproduce, for which it synthesizes its RNA, on which proteins can be synthesized, which, in turn, will form a viral particle. But as for the RNA of herpes viruses, there was no difference between "sick" samples and "healthy" ones; similarly, there was no difference in the RNA of the Epstein-Barr virus, which is also sometimes considered as a factor of Alzheimer's syndrome.
Then the researchers tried to find not RNA, but the DNA of the virus, which would indicate that the virus actually exists, although it sleeps in the host genome. But there was no difference in DNA between "alzheimer's" brain samples and "healthy" samples.
As the portal writes The Scientist, supporters of the viral hypothesis of Alzheimer's disease point to a number of other works in which this difference could still be found, and explain the new data by the fact that this time they used not very sensitive methods that do not allow detecting the virus in the dormant stage. Another argument against it is that the virus can be active at an early stage of the disease, and then falls asleep again, so that it becomes difficult to detect it in samples taken from deceased patients. (True, even in cases where the virus was found in abundance, it was also searched for in postmortem samples.)
On the other hand, as the "viral" skeptics say, even if there is a connection between the herpes virus and Alzheimer's syndrome, it is still difficult to understand where the cause is and where the effect is. After all, it may be that because of the disease, it is easier for the virus to enter the brain and it is easier to multiply in it. Anyway, the story of Alzheimer's syndrome and herpes is far from over.
Here we can recall a friend's recent work about the herpes virus and multiple sclerosis: we recently wrote that the relationship between the virus and multiple sclerosis could not be clarified for a long time because researchers did not distinguish between two varieties of the virus, HHV6A and HHV6B. However, the article about Alzheimer's syndrome says that traces of HHV6A, HHV6B and other varieties of the virus were searched separately.
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