Viruses responsible for Alzheimer’s disease discovered

The Lancet published the results of a high-profile study by scientists that suggests that people who survived covid have an increased risk of experiencing Alzheimer’s disease. In the meantime, another scientific work has appeared, which provides convincing evidence in favor of the viral nature of this neurological disease, which is becoming more widespread in the world. According to the latest data, Alzheimer’s is caused by successive infection with two very common and seemingly harmless viruses: herpes simplex and chicken pox.

Alzheimer’s disease, which is rapidly spreading across the planet, is called the disease of civilization. It has become the most common form of senile dementia (dementia): it accounts for 60 to 80% of cases of this condition. In Russia, the exact statistics of the spread of Alzheimer’s disease is unknown, but experts suggest that there are at least 2.4 million such patients over 65 years of age. And in recent years, patients with dementia have begun to get younger, which is putting even more pressure on already battered healthcare systems.

Alzheimer’s disease can begin almost insidiously, often masquerading as the forgetfulness of old age in the first months or years. So far, science has not established the exact cause of its development. However, the version of its viral nature remains one of the main ones – and finds more and more evidence.

During life, a person comes into contact with a huge number of viruses, and most do not cause much harm to the body and leave it to the end. However, some remain in the body in a dormant state for the time being. And they can be activated under certain circumstances. These include herpes viruses, represented by a family of 9 types. Including the herpes virus of the first type (HSV-1), which everyone knows as the cause of colds on the lips. Or the varicella-zoster virus (VZV), which usually causes chickenpox and sometimes shingles.

A recent study by scientists from Tufts University and Oxford University showed that just these two dormant viruses in the body can act as the starting mechanism for the development of Alzheimer’s disease – if the varicella-zoster virus triggers the activation mechanisms of the herpes simplex virus in the brain. The team of scientists came to this conclusion by conducting laboratory studies on a three-dimensional model of human tissue culture that mimics the brain.

Normally, the herpesvirus type 1 (HSV-1) lies dormant in the neurons of the brain, but when activated, it leads to the accumulation of tau and amyloid beta proteins, as well as loss of neuronal function: all of these characteristic features are observed in patients with Alzheimer’s disease. . Activation of the dormant virus in brain neurons, in turn, causes infection with the varicella-zoster virus, which creates additional inflammatory triggers.

The researchers noticed that VZV-infected samples began to produce higher levels of cytokines, proteins that are often involved in triggering the inflammatory response. VZV, on the other hand, causes inflammation in the brain, which can lead to the activation of dormant HSV and increased inflammation, plaque formation, and accumulation of damage to neurons and cognitive functions. The results of this study are published in the Journal of Alzheimer’s Disease.

Scientists note that a lot of facts have already been collected in the world in favor of the fact that the herpes virus is associated with an increased risk of developing Alzheimer’s disease. However, until now, the sequence of events that viruses create to set the disease in motion has been unknown. Now the first evidence of these events has appeared.

Meanwhile, according to the World Health Organization, an estimated 3.7 billion people under the age of 50 have been exposed to HSV-1 (the one that causes cold sores). In most cases, it is asymptomatic, being dormant in nerve cells. When the virus activates, it can cause inflammation in the nerves and skin, resulting in open sores and blisters. Most carriers will have very mild or no symptoms before the virus goes dormant.

The varicella-zoster virus (and this is also a type of herpes) is also extremely common, with about 95% of people becoming infected before the age of 20 years. VZV can also remain in the body, entering nerve cells and then entering a dormant state. Primary infection causes symptoms of a fever with a skin rash (chickenpox), but later in life, VZV can reactivate and cause herpes zoster, a disease characterized by skin blisters and nodules that form in bands and can be very painful. One in three people develop shingles during their lifetime.

Among other risk factors for the development of Alzheimer’s disease, other infections are also called today, as well as traumatic brain injuries, obesity, and alcohol abuse. In addition, today there is more and more evidence in favor of the fact that the risk of developing Alzheimer’s increases dramatically after suffering COVID-19, which, by the way, can also cause reactivation of the VZV and HSV-1 viruses. There are also many reports of long-term neurological consequences of infection with the SARS-CoV-2 virus for some patients, especially the elderly.

Recently, The Lancet published a publication with data from large-scale studies that convincingly indicate that COVID-19 significantly reduces the intellectual abilities of the population, leads to cognitive impairment and increases the risk of Alzheimer’s disease. According to its authors, in a number of patients who survived covid, even in a mild form of patients, the level of a marker of Alzheimer’s disease, the tau protein, increases, and IQ decreases by 0.6-1.8 points even after mild covid. And a study by Portuguese scientists showed that the incidence of Alzheimer’s disease after covid increases by 3.5 times.

“SARS-CoV-2, like any virus that causes severe inflammation, can significantly increase the risk of developing neuroinflammation, which creates the prerequisites for the formation of Alzheimer’s or Parkinson’s disease,” says Vyacheslav Dubinin, professor at the Department of Human and Animal Physiology at the Moscow State University Biofaculty, neurobiologist and immunologist. – The fact that the herpes virus of the first type, which many consider a harmless cold on the lips, like the chickenpox virus, remains in the neurons of the brain for life and leads to an increase in inflammatory status, which increases the risk of developing Alzheimer’s disease in old age, has long been known. And even a sluggish inflammatory process during a coronavirus infection can affect the body in the most unexpected way.