A growing number of COVID "long-haulers" suffer from persistent symptoms long after the initial infection. According to experts, many of those symptoms appear connected to COVID-19's effect on the brain and nervous system.
From Lungs to Brain
Government surveys reveal that millions of people in the U.S. live with neurological symptoms that are linked to long COVID. According to Dr. Robyn Klein from the Center for Neuroimmunology and Infectious Diseases at Washington University School of Medicine in St. Louis, it is considered a public health crisis.
During the early stages of the pandemic, health experts focused on the effect of SARS-CoV-2 on a person's lungs. However, the virus appears to do most of its damage to the brain indirectly.
The viral infection in the body triggers an immune response, leading to brain inflammation. This inflammation can persist long, even after the virus has been cleared. Scientists believe that the brain may be especially vulnerable to COVID because the disease weakens the blood-brain barrier, which typically protects the organ from both pathogens and immune cells that follow them. They also consider the possibility that COVID-related inflammation affects the vagus nerve, the longest and most complex of the cranial nerves. It carries information between the body and brain that is needed for memory and attention.
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Effect of COVID to the Human Brain
Evidence shows that even a mild COVID can cause long-term effects on a person's immunity and affect the brain and nervous system. Long COVID also has some striking similarities to autoimmune diseases, which happen when the immune system mistakenly attacks healthy cells.
In a separate study, Dr. Troy Torgerson from Allen Institute for Immunology and his colleagues studied blood samples from 55 people who showed symptoms at least 60 days after getting COVID infection. They saw persistent ongoing immune activation in about half of the population. Once the immunity gets fired up, it can affect the brain even if SARS-CoV-2 does not infect brain cells.
To understand how long COVID affects the human brain, researchers conducted a study involving mice that developed a mild version of the disease. A month after they got infected, these animals showed cognitive deficits. They do not have the virus anymore and are no longer ill, but they cannot remember and recognize things. Klein believes that one reason could be the weakening of the blood-brain barrier due to infection.
This allowed the body's immune response to affect the brain cells of these animals. Such a condition results in inflammation that causes subtle but significant changes in the brain. It does not mean many dying neurons, but eliminating the connections between neurons.
The researchers suspect something similar happened to the synaptic connections in the brains of people who had long COVID. She also suggests that it can happen even in people who don't get very sick. Drugs may be administered to reduce inflammation to protect the brain after an infection. In the meantime, vaccination is also promoted to reduce the risk of developing long COVID.
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