The neurological mystery of COVID-19

(Washington) There were crowds at the American Association for the Advancement of Science (AAAS) annual meeting in early March for the conference where three luminaries discussed the enigma of the impact of COVID-19 on the brain. Their most worrying conclusion: certain infections would accelerate underlying neurodegenerative disorders.

Smell and confusion

Problems with smell were the first neurological symptom to worry people during the pandemic, according to Kiran Thakur, a Columbia University neurologist who has published several of the most important studies on the neurology of COVID-19. “Then we talked about concentration and memory problems. But eventually, these problems subside over the months. »

“It is very difficult to distinguish the effect of illness from the effect of hospitalization. But there appears to be a direct effect of COVID-19 on long-term quality of life in older adults. We must take advantage of the abundance of data on patients of the pandemic to get to the bottom of the question, ”underlines the researcher.

Parkinson’s

Stanley Perlman is a University of Iowa microbiologist who has dedicated his career to studying coronavirus-related smell issues. “It has long been suspected that some infections cause damage to the airways,” says Dr.^r Pearlman. But it was difficult to study the issue in humans, because they are mild symptoms and most smell problems are transient and due to nasal congestion. My work on mice led me to think that there could be neurological damage. With COVID-19, I was able to show that it’s not just in the airways, but also in the brain. In animal models of COVID-19, for example, we see damage to the dopamine system [une molécule du cerveau liée à plusieurs problèmes psychiatriques et neurologiques] and neurological disorders of locomotion. I recently unearthed reports of more frequent cases of Parkinson’s in victims of severe cases of Spanish flu in 1918.”

Avindra Nath of the National Institute of Neurological Disorders in Bethesda, a suburb of Washington, goes further. “The big question that needs to be investigated in terms of the neurological impacts of COVID-19 is the possibility that it is accelerating certain neurodegenerative diseases,” says Dr.^r Nath, who was one of the first to describe neurological symptoms of COVID-19, in 2020. “We also have to see how vaccination influences this risk of neuropathogenesis. »

Blood-brain barrier

One of the big puzzles of the neurological impacts of COVID-19 is that almost no fragments of SARS-CoV-2, the coronavirus that causes COVID-19, are found in the brain.

“It seems that in the early stages of COVID-19, when there’s a ‘cytokine storm’ [une réaction immunitaire très forte]the blood-brain barrier is disrupted, explains Dr.^r Perlman, but it doesn’t seem to lead to SARS-CoV-2 entering the brain. »

Long-term dysregulation of the immune system is one of two possible explanations for long-term neurological effects, according to Dr.^r Nat. “The other explanation would be a persistence of SARS-CoV-2 in the central nervous system or the respiratory tract, but there would have to be hidden reservoirs, because we don’t see much on the population level. , says the neurologist from Maryland. The few brain autopsies that have been done in patients who have died from COVID-19 have shown vascular damage that could be due to an autoimmune disorder, immune system antibodies that attack brain vessels or neurons. I wouldn’t be surprised if we see this same brain damage in long-term COVID cases, if we do a brain autopsy after a death. »

Antivirals

One avenue of treatment is to use antiviral drugs, not to directly target SARS-CoV-2, but to stabilize the immune system.

“It may be due to a faster return to normal functioning of the immune system, says Dr.^r Nat. We have the same track for other neurological conditions linked to viruses. After the presentation by the three experts, a good part of the twenty pointed questions posed by doctors and researchers in the audience related to these drugs. “For example, if we think that molecules of the immune system are attacking certain regions of the brain, we could try drugs that block these molecules,” says Dr.^r Nat.

AIDS

The COVID-19 pandemic is an opportunity to learn more about the neurological impacts of infections affecting organs other than the brain. “We have been talking for a long time about cases of dementia associated with AIDS, for example, says Dr.^D Thakur. But we never had enough cases to study the question. With SARS [qui a touché Hong Kong et le Canada en 2003] and MERV, two other diseases caused by coronaviruses, there was talk of brain damage, but there were too few cases to be sure. There was no brain autopsy. »

Multiple sclerosis

Another conference at the AAAS conference focused on a similar area: the possibility that multiple sclerosis is closely linked to a mild infection of a herpes-like virus, responsible in particular for mononucleosis.

“I believe we are seeing a discovery similar to that of the neurological impacts of COVID-19,” said Alberto Ascherio, a Harvard University neurologist who demonstrated last year in the journal Science that the Epstein-Barr virus (EBV) increases the risk of multiple sclerosis by 32 times, after having followed 10 million soldiers for 15 years, from the start of their military career. More than 90% of the population is infected with EBV during their lifetime, but only one in 1000 people will have multiple sclerosis. The conference of the D^r Ascherio and his Stanford colleague Larry Steinman, who discovered the first drugs for severe multiple sclerosis, were also one of the most popular in the congress.

“I am convinced that by now knowing the role of EBV in the development of multiple sclerosis, we will be able to find new drugs,” says Dr.^r Ascherio. And I can also say that people who have never had EBV probably have very little risk of having multiple sclerosis. »