SINC/Eva Rodríguez
01/20/2024 – 08:00h.
Why do some Covid-19 patients develop long-term symptoms and others do not? This is a question that still does not have a concrete answer. Approximately 20% of diagnosed patients and around 5% of all people infected with SARS-CoV-2 develop prolonged symptoms, so-called persistent covid.
Symptoms can include fatigue, discomfort after exertion, and cognitive impairment, and affect multiple organs. Although previous studies have shown that people with so-called long covid show signs of immune dysfunction, persistent activation of immune cells and production of autoimmune antibodies, the cause of this is not well known and diagnostic biomarkers are not correctly defined.
Because there is currently a lack of effective treatment, a scientific team conducted a study of the blood serum of 113 patients. Of them, some were completely recovered and others had persistent covid, in addition to taking a healthy control group as a reference.
Using high-throughput proteomics technologies, they measured serum levels of 6,596 human proteins in the participants. Likewise, they followed up those patients with confirmed acute Covid-19 for up to a year, and a blood serum sample was taken again at 6 and 12 months. The findings are published in the journal Science.
“Of all the patients we followed up to a year after their initial SARS-CoV-2 infection, 40 had persistent Covid at the 6-month follow-up. These and 39 additional healthy controls were analyzed in depth, with more than 7,000 proteins measured in blood, at multiple time points,” Carlo Cervia-Hasler, from the Department of Immunology at the University Hospital of Zurich (Switzerland), who leads the study, explains to SINC.
The analysis of these proteins showed that a part of the immune system, called the complement system and whose main mission is to eliminate pathogens, was activated in persistent covid patients. In healthy people, the complement system fights infections and eliminates damaged cells from the body. However, if after an infection it does not return to its basal state but remains activated, it can also damage healthy cells in the body.
“After having observed an excessively active complement system in patients with persistent covid, we looked for possible damage caused by said system. Indeed, we found blood markers of tissue damage, including red blood cells, platelets and blood vessels,” explains the researcher.
Biomarkers for diagnosis and treatment
Patients who experienced persistent Covid showed changes in blood serum proteins, suggesting to researchers that they suffer from ongoing thromboinflammatory responses.
“This study identifies possible biomarkers for the diagnosis of long covid and could provide information on treatment. It is important to confirm these findings in other cohorts of patients with more individuals and different patients,” adds the researcher.
Wolfram Ruf, a scientist at Johannes Gutenberg University in Germany, states in a related article: “While therapeutic interventions with coagulation and complement system inhibitors in acute Covid produced mixed results, their specific pathological characteristics suggest possible interventions.” for clinical trials.
For his part, Cervia-Hasler emphasizes: “This novel mechanism has different implications. On the one hand, it adds scientific understanding of this condition and supports additional research on the biological mechanisms underlying this clinical syndrome. In addition, we have been able to diagnose the syndrome of “Persistent Covid in patients with active disease six months after initial SARS-CoV-2 infection. As these patients often face psychiatric stigma, objective blood testing is urgently needed to ensure optimal care.”
Finally, the work offers a basis to continue investigating treatments aimed at the pathways that have been observed to be excessively active in people affected by this type of long-term covid. “New effective treatments are urgently needed,” concludes the expert.
Now, the research group is asking another series of questions to be resolved in future studies, such as whether these treatments are useful against long covid and whether they are safe or which patients benefit the most and at what point in the course of the disease.