several hypotheses to explain this phenomenon which affects millions of people

published on Sunday, October 02, 2022 at 07:00

The long Covid is manifested by symptoms such as chronic fatigue, shortness of breath, or even brain fog, several months after a Covid-19 infection, many teams are working around the world to understand the causes.

The “Covid long” remains a mystery for research, even if several hypotheses are on the table to explain it. This phenomenon affected, in 2020 and 2021, 145 million people worldwide, according to the Institute for Health Metrics and Evaluation, based in the United States.

Europeans are “at least 17 million” to be affected, according to a recent estimate by the World Health Organization (WHO). This would represent between 10 and 20% of people who have been infected with the virus.

Fatigue, cough, shortness of breath, intermittent fever, loss of taste or smell, difficulty concentrating, depression… the long Covid is manifested by one or more symptoms from a long list, generally within three months after infection and persisting for at least two months. The syndrome affects twice as many women as men. “There are no symptoms really specific to long Covid, but they still have certain characteristics: they are fluctuating with fatigue that remains in the background, they seem to be exacerbated after intellectual or physical effort and become rarer over time”, summarizes Olivier Robineau, infectious disease specialist at the Tourcoing hospital center and coordinator on long Covid at the Agency. national-emerging infectious diseases.

Many teams are working around the world to understand the causes of these symptoms. In France, for example, the Hôtel-Dieu hospital (AP-HP), the University of Paris and Inserm launched a study at the end of 2020 on long Covid within the “ComPaRe” cohort: “2,500 patients are monitored very regularly, which should allow us to understand the variations in the manifestations of the disease over time”, explains Dr. Viet-Thi Tran, co-investigator of the cohort. But the variability of the symptoms and their non-specific nature makes research difficult. So far, several hypotheses are studied by scientists.

Several hypotheses

One of them is the persistence of the virus in the body in some individuals. Thus, at the beginning of September, a study published in “Clinical infectious diseases” concluded that the Spike protein (the key allowing SARS-Cov 2 to enter cells, editor’s note) was present in patients with long Covid. This suggests viral replication or the persistence of viral remnants long after the initial infection. A live virus or remnants of virus could maintain an inflammatory activity, perhaps at the origin of the symptoms. These results, however, are not not found by other teams.

Other avenues exist. The virus would have disappeared after the infection but the initial inflammation, once started, would have caused a dysregulation of the immune system. The so-called “tissue damage” hypothesis evokes the role of the initial infectious episode in the appearance of lasting lesions in certain organs. Studies have further demonstrated damage to blood vessels as a result of the infection.

A course of care at the Hôtel-Dieu

For each of these hypotheses, the data is not yet very solid”, says Olivier Robineau, betting that “we are not going to find a single cause to explain the long Covid”. “The causes may not be exclusive, they could be associated, even succeed each other in the same individual and be different in different individuals,” he says. It is therefore difficult to find a solution for these long Covid patients.

At the Hôtel-Dieu in Paris, a protocol called “CASPER” has been offering for a year a course of care to patients for half a day: “They meet an infectious disease specialist or an internist, a psychiatrist then a doctor specializing in sports rehabilitation”, explains Professor Brigitte Ranque, specialist in internal medicine, at the origin of this circuit. “In the team’s experience, a majority of the symptoms can be attributed to ‘functional somatic disorders’ (the symptoms result from an imbalance in the functioning of the central nervous system, editor’s note). behavior is often associated with supervised physical activity”. “The patients are called back three months later: the majority of them are better, more than half say they are cured”, details Professor Ranque. “But about 15% are not improved at all,” she admits.

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