More than three years after the start of the epidemic, Covid-19 retains its share of mystery. The causes of long Covid are part of this. Indeed, this disorder remains poorly understood and several explanations compete. Two recent studies provide possible explanations for this syndrome, one evoking the joint effect of after-effects in various organs, the other a mechanism at the neuronal level.
There is “concrete evidence that different organs undergo changes” after hospitalization linked to Covid, declared, during a press conference, Christopher Brightling, co-author of a study published Friday September 22 in the Lancet Respiratory Medicine. This work is based on MRIs carried out in 259 patients who were hospitalized for Covid in 2020-2021. They were compared with examinations carried out on around fifty people who had never been infected.
Nearly a third of Covid patients presented “abnormalities” in several organs, several months after leaving hospital. These organs include the brain, lungs or kidneys and, to a lesser extent, the heart and liver. “Follow-up studies of patients hospitalized with Covid-19 report a decline in kidney function in up to 30% of patients,” the researchers indicate.
For example, specialists have identified lesions of the white matter of the brain, a phenomenon which can be associated by scientific literature with a slight cognitive decline. “These results highlight the diminished neurological reserve and vulnerability of post-hospitalized patients with Covid-19,” explains the study.
The joint effect of aftereffects on various organs
For the authors of the study, as well as independent observers, these results open up a possible explanation for long Covid, that is to say the persistence of lasting after-effects several months after infection. This disorder, which however lacks a consensual definition, is still poorly understood on a physiological level, with several explanations competing without being necessarily exclusive.
Friday’s study suggests that long Covid “is not explained by serious insufficiencies concentrated in a single organ” but rather “an interaction between at least two anomalies of (different) organs”, still moving forward in the Lancet Respiratory Medicine pulmonologist Matthew Baldwin, who was not involved in the study. The latter adds that “these results highlight the need for multi-targeted therapies and integrated multidisciplinary monitoring services for patients recovering after admission to hospital with Covid-19”.
A mechanism concentrated in the brain
A second study, published a week earlier in the journal eBiomedicine, rather opened the trail of a mechanism concentrated in the brain. “There is no longer any doubt that SARS-CoV-2 invades the brain and has profound effects on it, even if not all parts of the brain are equally vulnerable to infection,” emphasizes- She.
Led by a team from Inserm, this study looked at around fifty patients, some of whom suffered a drop in their testosterone levels linked to an alteration by the virus of certain neurons regulating reproductive functions. The researchers then measured the cognitive functions of these patients, only to note poorer performance when this category of neurons was affected. These results “suggest that the infection can lead to the death of these neurons and be the cause of certain symptoms which persist over time,” says Inserm in a press release.
In May 2023, another study from the National Institute of Health and Medical Research (Inserm), published in the journal Nature Communications, estimated that long Covid mainly affected people whose immune systems were less efficient. These patients are unable to defend themselves against the virus which settles in the mucosa where it can persist. More recently, in a study published at the end of August in the journal Nature“researchers have shown the presence at the beginning of the disease of two molecules at high levels abnormally high in patients with long Covid,” infectious disease specialist Olivier Robineau recently explained to L’Express.
Long Covid manifests itself with one or more symptoms from a long list, usually within three months after infection and persisting for at least two months. Symptoms that cannot be explained by other diagnoses and have an impact on daily life. In France, “Long Covid” has affected 4% of adults, or 2.06 million people over 18, with a small proportion (1.2%) declaring that they are seriously hampered in their daily activities, according to a Health study. public France carried out last fall and the results of which were revealed in June.
The vast majority of patients (90%) suffering from long Covid, however, see their symptoms slowly improve after two years, with the others experiencing rapid improvement or, on the contrary, persistence of their disorders, specifies a study published in May by the Dr Viet-Thi Tran, epidemiologist (Université Paris Cité/AP-HP), with 2,197 patients from the “ComPare” cohort suffering from long Covid, followed regularly.