You may know someone who, after passing COVID-19, tends to forget certain things, get headaches, or have not yet fully regained your sense of smell. These symptoms are included within the phenomenon of brain fog in which a part of the population has been plunged as a result of the pandemic. If it lasts over time, its effects can end up being harmful.
The nervous system suffers
Although infection with the SARS-CoV-2 coronavirus primarily affects the respiratory systemmost patients suffering from COVID-19 show neurological symptoms as loss of smell, headache, sleep disorders and memory deficit.
On the other hand, several studies indicate that patients with neurodegenerative disorders such as Alzheimer’s disease are more prone to more severe disease.
Taken together, these signs are a clear indicator that the virus is also affecting the nervous system. That is why it is increasingly important to study what the long-term effects and sequelae of this disease in the brain may be.
Trojan horse and neural highways
But how does SARS-CoV-2 get to the brain? Reaching this organ directly is not easy because it is surrounded by a true wall of blood vessels known as the blood-brain barrier. Despite this, SARS-CoV-2 is capable of circumventing this protection by different mechanisms.
To start with, you can send signals that cause the blood-brain barrier to be modified. Furthermore, it is able to enter our own cells and use them as a vehicle to sneak into the brain. The strategy is a true Trojan horse, since the pathogen is disguise of something recognizable by our body to be able to cross barriers that would otherwise be insurmountable.
Finally, SARS-CoV-2 can also travel through neurons, which are distributed throughout our body forming a network of nerves. The virus is capable of reaching one of the neuronal extensions and moving through them as if they were a highway that ends in the brain. Precisely in the nose, the place of entry and infection of the virus, is the olfactory nerve, which could be a direct entry route to the brain.
The COVID-19 virus can also affect the brain indirectly. This is what happens when our immune system reacts to the presence of foreign microorganisms by releasing molecules called cytokines. These molecules act as a call signal and induce an inflammatory reaction in the tissue where they are located.
This response, in principle, is beneficial, because it manages to attract the different cells of the army that will fight against the infection. Nevertheless, if it lasts over time, a state of chronic inflammation is created that can be very dangerous and compromise the functions of different organs, including the brain.
“In the case of SARS-CoV-2, its ability to induce a generalized inflammatory state in our body can facilitate the progression of neurodegenerative diseases.“
Precisely in individuals with diseases associated with aging, this state of chronic inflammation is prevalent. Specifically, Alzheimer’s patients are known to suffer from neuroinflammation. This means that the immune system of your brain is active continuously and over time, causing damage to structures and greater neuronal death and neurodegeneration.
Can COVID-19 cause Alzheimer’s?
Now, then, what is the link between neurodegenerative processes and COVID-19? The relationship between viral infections and neurodegeneration has been known for a long time, and as can be deduced, the point at which both pathologies converge is inflammation.
In the case of SARS-CoV-2, its ability to induce a generalized inflammatory state in our body can facilitate the progression of neurodegenerative diseases. In addition, the cytokine storm that is generated as an exacerbated defense mechanism is capable of deregulating physiological parameters. For example, the number of oxidizing molecules increases in neurons due to an imbalance in iron levels that makes the damage worse. This leads to more neuronal death and greater neurodegeneration.
In favor of this theory, some studies show that patients with COVID-19 present neuronal losses in the same regions of the brain where damage occurs in Alzheimer’s disease. Furthermore, biomarkers of neurodegeneration are increased in many patients hospitalized for COVID-19.
It is clear that SARS-CoV-2 has a more profound impact on the brain of patients than initially thought. A better understanding of the interaction of this virus with the central nervous system could prevent the development of neurodegenerative diseases such as Alzheimer’s, also worldwide and, for the time being, without a cure.
Juana Andreo López, FPI Researcher. Researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and at the Malaga Biomedical Research Institute (IBIMA), Malaga University; David Baglietto Vargas, Beatriz Galindo Senior Distinguished Researcher. Researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and at the Malaga Biomedical Research Institute (IBIMA), Malaga University and Miriam Bettinetti Luque, predoctoral researcher at the Center for Network Biomedical Research in Neurodegenerative Diseases (CIBERNED) and the Malaga Biomedical Research Institute (IBIMA), Malaga University. This article was originally published on The Conversation. Here you can read the original.
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