We’ve moved on, but science hasn’t - new findings on COVID-19 and the brain

It's not widely known that even common infections like the flu or a cold can enter the fluid surrounding the brain—the cerebrospinal fluid. This is one of the reasons why people feel sick and exhausted, and develop headaches during viral infections.

Many viruses have the potential to impact the nervous system and the brain, and this has been seen throughout history. Perhaps that’s why I’ve made a personal vow to Brainwoosh that COVID-19 should not be treated as drastically different from other neurological infections that humanity has overcome before.

But I haven't forgotten or suppressed the memory of early spring 2020. That year, the world suddenly faced a single, overwhelming crisis—the emergence of a new virus that affected all of us in different ways, whether physically, emotionally, or financially.

When things started to get ugly I wrote to my previous boss - that if it came to a situation where no one turned up at the department - he was welcome to ring me That was then.

And now an interesting study has emerged.

A bit about how this virus and the nervous system
COVID-19 is primarily known as a respiratory disease, but it also affects other organs, including the nervous system - like other viruses do.

Many people with COVID-19 experience neurological symptoms, ranging from mild issues like headaches and loss of smell to severe conditions such as strokes, encephalitis, and Guillain-Barré Syndrome. That's a dangerous condition where the peripheral nerves gradually lose function - it literally crawls from the hands and feet upwards ...

Research has shown that about one-third of COVID-19 patients have some form of neurological involvement. These symptoms can appear during the acute phase of the illness or weeks later, sometimes as the first sign of infection.

The nervous system complications associated with COVID-19 affect both the central nervous system, which includes the brain and spinal cord, and the peripheral nervous system, which connects the brain and spinal cord to the rest of the body.

Some patients experience seizures, memory problems, muscle weakness, or difficulty walking. More serious cases may involve inflammation in the brain, nerve damage, or impaired blood flow leading to strokes.

How the virus reaches the brain
SARS-CoV-2, the virus responsible for COVID-19, enters human cells using a protein called ACE2 as an entry point. This protein is present not only in the lungs but also in brain cells, making the nervous system a potential target.

The virus may invade the brain directly through the olfactory nerve, which connects the nose to the brain. This could explain why many COVID-19 patients report a sudden loss of smell.

Or the virus travels through to the brain via the bloodstream. Some studies suggest that the virus might reach the brain by infecting immune cells, which then carry it into the nervous system.

Another way COVID-19 might affect the brain is indirectly through an intense immune response that causes inflammation in the brain. The immune system releases inflammatory molecules called cytokines to fight the virus, but the cytokines can damage the blood-brain barrier, allowing harmful substances to enter the brain.

This immune response may cause neurological symptoms even if the virus itself is not present in the brain. In some cases, patients make antibodies to the virus, that mistakenly attack their own nervous system. That can lead to complications such as demyelinating disorders, where the protective coating of nerves is damaged like the Guillain-Barré Syndrome mentioned above.

Another way the virus can damage the Brin is by triggering blood-clotting problems, leading to strokes and other complications.

Oxygen deprivation due to severe respiratory illness can also harm brain cells. However, some of the patients had neurological symptoms without any respiratory issues, suggesting that the virus might attack the nervous system independently of the lungs.

Findings from the new study
A recent study investigated the neurological effects of COVID-19 by analyzing brain fluid/CSF from 27 patients who had both COVID-19 and symptoms of nervous system involvement.

Researchers tested a sample of their brain fluid (cerebrospinal fluid/CSF) for the presence of the virus and white blood cells - and evaluated their clinical neurological symptoms, examined their brain scans and immune system responses in blood tests.

This study identified a wide range of neurological conditions, including strokes, encephalitis, Guillain-Barré Syndrome, and cognitive impairments. They found that in about one-third of the cases, the virus was detected in the CSF, providing evidence of direct infection of the nervous system. The presence of SARS-CoV-2 in the CSF was linked to more severe neurological symptoms.

Some patients with negative virus tests in the CSF still exhibited significant nervous system damage. This suggests that multiple mechanisms, including direct viral invasion of the brain and immune-mediated damage, contribute to the neurological effects of COVID-19.

Long-term neurological effects of COVID-19
Some people experience neurological symptoms long after recovering from the initial infection, a condition often referred to as "Long COVID."

These symptoms include brain fog, fatigue, difficulty concentrating, memory problems, and persistent headaches. In some cases, individuals develop movement disorders, sleep disturbances, or psychiatric conditions such as anxiety and depression.

The underlying causes of Long COVID remain unclear, but researchers believe that lingering inflammation, immune system dysfunction, and possible long-term viral persistence may be involved.

And they continue to investigate whether the virus remains hidden in the body or if the immune system continues to cause damage long after the initial infection has cleared.

About the scientific paper:

First author: Carla de Oliveira Cardoso, Brasil
Published: PLoS One, March 2025
Link to paper: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0312621