COVID-19 and RSV: A simple nasal swab to spot stealthy viruses

Politicians and Public Health Agencies refer to certain, limited sources to detect early warning signs of an emerging disease. By monitoring animals capable of transmitting the infection to humans. But it remains complex to determine which of the hundreds or thousands of new viral variants represents a real danger. Many respiratory epidemics thus remain unexplained or detected late. And by the time the epidemic occurs, it is too late to contain its spread.

“Identifying a dangerous new virus is like looking for a needle in a haystack,”

writes lead author Ellen Foxman, associate professor of medicine and immunobiology: “We just found a way to drastically reduce the size of the haystack.”

The study starts from an observation made by the same team in 2017: nasal swabs taken from patients suspected of respiratory infections are tested to detect the specific signatures of 10 to 15 known viruses. Most of the tests come back negative. However, in a few cases, swabs from those who tested negative for the usual suspect viruses still show signs of activating antiviral defenses.

which suggests the presence of an as yet unidentified stealth virus.

The telltale sign or marker consists of a high level of a single antiviral protein made by the cells that line the nasal passages. Based on this discovery, the researchers applied comprehensive genetic sequencing methods to ancient samples containing the protein and, in one sample, found an unexpected influenza virus, called influenza C. Analysis of other sets of swab samples tested for this immune system biomarker thus identify 4 other undiagnosed cases of COVID-19 at the time.

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Thus, testing for an antiviral protein made by the body, even if tests for known respiratory viruses are negative, can identify nasal swabs with unexpected viruses.

Detection of this biomarker using swabs collected during routine patient care, could therefore also help to restrict the search for stealthy pathogens. Samples that carry the biomarker can be analyzed using more complex genetic testing methods to identify unexpected or emerging circulating pathogens, which can enable a more coordinated response from health systems.

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