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A British study, published on July 8, has provided a better understanding of the diversity of brain damage that Covid-19 can cause.
She had just left the hospital after being treated for symptoms of Covid-19, such as persistent fever, cough, and breathing problems. But a day later, the 55-year-old Briton started hallucinating, seeing monkeys and lions in her house. In addition to this, the 50-year-old felt like she was being persecuted and felt compelled to take off and put on her coat several times in a row.
The woman is one of 43 patients with severe neurological complications from Covid-19 who have been studied by British researchers. Their conclusions, published Wednesday July 8 in the scientific magazine Brain, reinforces the conviction of the scientific world that the Sars-CoV-2 virus does not attack only the respiratory tract. And that this virus can cause severe damage, especially to the brain.
A slightly neurotropic virus on the edges
“We had to wait for the virus to migrate from China and come to Europe before scientists in Italy began to alert us to its neurological effects”, recalls Pierre-Marie Lledo, director of the neurosciences department of the Institut Pasteur, who directs the “task force” to study the consequences on the brain of the coronavirus, contacted by France 24. The simultaneous loss of taste and smell was among the first clues to this little-known aspect of the pandemic.
“This study makes it possible to see more clearly on the categories of neurological damage that Sars-CoV-2 can cause”, specifies Pierre-Marie Lledo. And they are many. British scientists have found different types of encephalitis, ADEM (an acute inflammatory disease of the central nervous system that usually affects children), cases of Guillain Barré syndromes (a condition that attacks the nervous system and causes paralysis) or more strokes (strokes). These complications, which seem to affect only a small minority of infected people, can occur up to 6 days before and 14 days after the onset of the more classic symptoms of Covid-19.
These findings suggest that Sars-CoV-2 has “a tendency to neurotropism, that is to say that it has an appetite for neurons”, notes the researcher from the Pasteur Institute. The most famous of the neurotropic viruses is that of rabies, which attacks almost exclusively the neuronal system. However, the current coronavirus remains above all a respiratory virus. But one does not prevent the other. “We know that the receptor which allows Sars-CoV-2 to enter cells is present in the respiratory tract, but it is also present on cells of other organs, such as the brain or the liver”, explains Nicolas Locker, professor of virology at the University of Surrey, contacted by France 24. This researcher would not be surprised to learn that the coronavirus also leaves consequences in the liver.
Less severe lung symptoms than brain
The long history of viruses also proves that these pathogens are not exclusive in their target. The Spanish flu of 1918 left behind patients who later developed complications in the brain. The Zika virus, which passes through the blood, has been shown to cause brain damage such as microcephaly. Even during previous coronavirus epidemics – those of SARS in 2002 and of Mers in 2012 – “there were signs indicating effects on the brain, but not enough elements to establish a clinical neurological picture”, underlines Pierre-Marie Lledo. “It is quite common for a virus to be able to migrate, and it is therefore not surprising that Sars-CoV-2 causes secondary damage to the brain,” summarizes Nicolas Locker.
What seemed more surprising to the British researchers is that, for some of the hospitalized patients, “the pulmonary symptoms were relatively weak, while the neurological symptoms, them, were severe”, remarks Pierre-Marie Lledo. This is particularly the case for a sixties woman, already suffering for two years from a decline in cerebral capacities, who was admitted to the hospital after episodes of hallucinations, vision and speech disturbances. In his case, the damage of the virus to the brain was greater than that of the respiratory tract.
However, this study does not lead to the conclusion that people who are asymptomatic or have only mild symptoms are at risk of developing serious neurological complications. “The researchers looked specifically at what was happening in patients who were already very sick,” said Nicolas Locker. Above all, there are too few cases taken into account in this study to allow generalizations.
Chronic neurological consequences ?
On the other hand, the fact that some of these patients developed neurological complications up to two weeks after the onset of symptoms of Covid-19 “suggests that it will be necessary to adapt the monitoring of patients after their discharge from hospital for better take this risk into account, “said the virologist at the University of Surrey.
The study also calls for further exploration of the effects of the Sars-CoV-2 virus on the brain, according to the two specialists interviewed. For Nicolas Locker, it would be necessary in particular to determine “if the symptoms of Covid-19 are going to be more important for people who are likely to develop neurodegenerative diseases”. In other words, should these individuals be included in the population at risk alongside diabetics or people who already suffer from respiratory diseases?
The other fear raised by this study is that “Sars-CoV-2 could have chronic neurological consequences”, underlines Pierre-Marie Lledo. The researcher at the Institut Pasteur recalls that “for a reason that still eludes us, people seem to have recurrent versions of certain symptoms of Covid-19”. One of the main risks, currently studied at European level, is that the coronavirus can trigger chronic fatigue syndromes.