New Delhi, Aug 11 US researchers have identified a potential biomarker for long Covid that may help develop better diagnostics and potential treatments for the condition.
Currently, clinicians confer a diagnosis of long Covid based upon a collection of symptoms that patients develop after SARS-CoV-2 infection.
The study, reported in the journal Infection, details the detection of SARS-CoV-2 protein fragments within extracellular vesicles (EVs) -- tiny, naturally occurring packages that help cells share proteins, metabolites, and other materials.
"If a patient arrives in clinic and they relate the persistence of typical signs and symptoms of long Covid, 12 weeks or more after Covid-19 infection, I give them a presumptive diagnosis, but I don't have any blood tests or biomarkers to confirm this diagnosis," said William Stringer, from the Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Centre.
The new biomarker could be the first specific and quantifiable indicator for confirming long Covid.
The researchers collected and analysed blood samples from 14 patients over 12 weeks of aerobic exercise training (56 samples in all) in a clinical trial on long Covid.
The team found 65 distinct protein fragments from SARS-CoV-2 inside the EVs. These fragments come from the virus's Pp1ab protein -- an RNA Replicase enzyme which is key to how the virus copies itself and makes other viral particles.
This protein is found uniquely in SARS-CoV-2, and not in uninfected human cells, noted Asghar Abbasi, another researcher from Lundquist Institute.
Significantly, the researchers found that these viral peptides were demonstrated in each subject, but not in each blood draw, in the EVs of long Covid patients and were not detected in a separate control group of pre-pandemic EV samples.
Although the identified peptides originated from one of the virus's largest proteins, the researchers did not detect other comparably large proteins indicative of active viral replication.
The peptides contained in the EVs may be just molecular "trash" left over after the formation of new viral proteins, they said.
"We haven't run [our tests] on people without long Covid symptoms who are currently, or who were, infected with Covid," said Stringer.
"This raises the question: is this just continuing to take out the trash from the Covid-infected cell, or is this really ongoing replication someplace? I think that's the mechanistic issue that needs to be resolved in future studies."
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