Fatigue, depression, cognitive decline – these are the symptoms of post-COVID-19 syndrome – or Long Covid. It catches the affected person only a few weeks after the infection and how it develops remains a mystery.
Researchers at the University of Veterinary Medicine Hannover have now found and published in “The Lancet” that SARS-CoV-2 infection has a direct effect on the brain: proteins in nerve cells change their structure long after the infection is cured. When assembled, proteins are misfolded – an effect known in patients with Alzheimer’s and Parkinson’s disease. The researchers observed so-called plaques, protein layers that inhibit the function of nerve cells and thus lead to impaired concentration and memory in those affected. In addition to exhaustion, it is precisely these disorders that make Long Covid patients struggle.
We have been confronted with coronavirus and a pandemic for almost two years. A large complex of topics provides a lot of material for reports. Here is a selection of articles on new variants, symptoms such as Long Covid and vaccine news.
The security system of the brain has weaknesses
Veterinarians also found that SARS-CoV-2 infection activated immune cells in the brain. Our brain is one of the most protected areas of our body. Among other things, the blood-brain barrier ensures that only selected substances from our bloodstream can enter the central nervous system. It protects our brain from pathogens, toxins and mediators. But like any security system, the brain has its weaknesses. The gap used by viruses such as flu, FSME, dengue or herpes viruses is our sense of smell.
It has not yet been elucidated whether and by which SARS-CoV-2 actually enters the brain, but because up to 67 percent of patients with COVID-19 show neurological symptoms, coronaviruses appear to cross the blood-brain barrier. Neurological symptoms may include cognitive impairment, sleep disorders, headache, dizziness, depression, anxiety, gait disorders, and general fatigue. Sometimes the symptoms survive the acute infection, sometimes they do not reappear for weeks.
Some viruses enter the brain by infecting the olfactory nerve through the olfactory mucosa and then migrating through the nerve to the brain. The individual olfactory threads of the nerve run through the perforated bone plate of the skull – the so-called sieve plate – to the olfactory bulb. It transmits incoming signals to the brain for processing. This point is one of the few gaps in the blood-brain barrier. The immune system pays special attention here and produces messengers that activate the brain’s immune system, which is largely separate from the rest of the body.
Some brain cells respond to SARS-CoV-2
Microglial cells are an important part of this brain’s immune system. Hanover researchers have now observed that this cell type not only responds briefly to SARS-CoV-2 infection, but that the cells – at least in their test animals – remain active for 14 days after the actual infection has healed.
With signs of Long Covid, even poorly composed proteins appear in the brain. The cerebral cortex is particularly affected, and defective alpha-synuclein and tau proteins make it difficult for nerve cells to transmit data.
The researchers compared the neurodegenerative diseases Alzheimer’s and Parkinson’s, because even in Long Covid, only a certain area of the brain is affected, not the whole brain. According to study leader Franziska Richter Assencio, neurodegenerative diseases are characterized by selective sensitivity of individual areas of the brain. And the incorrect composition of alpha-synuclein and tau could explain the long-lasting symptoms. If this suspicion is confirmed in further studies, it would be one of the first approaches to the development of a specific drug against Long Covid.