The coronavirus that causes Covid-19, SARS-CoV-2, can spread within days from the airways to the heart, brain, and almost every organ system in the body, where it may persist for months, a study found.
In what they describe as the most comprehensive analysis to date of the virus’s distribution and persistence in the body and brain, scientists at the U.S. National Institutes of Health said they found the pathogen is capable of replicating in human cells well beyond the respiratory tract.
The results, released online Saturday, December 25, 2021, in a manuscript under review for publication in the journal Nature, point to delayed viral clearance as a potential contributor to the persistent symptoms wracking so-called long Covid sufferers. Understanding the mechanisms by which the virus persists, along with the body’s response to any viral reservoir, promises to help improve care for those afflicted, the authors said.
“This is remarkably important work,” said Ziyad Al-Aly, director of the clinical epidemiology center at the Veterans Affairs St. Louis Health Care System in Missouri, who has led separate studies into the long-term effects of Covid-19. “For a long time now, we have been scratching our heads and asking why long Covid seems to affect so many organ systems. This paper sheds some light, and may help explain why long Covid can occur even in people who had mild or asymptomatic acute disease.”
The findings haven’t yet been reviewed by independent scientists, and are mostly based on data gathered from fatal Covid cases, not patients with long Covid or “post-acute sequelae of SARS-CoV-2,” as it’s also called.
The coronavirus’s propensity to infect cells outside the airways and lungs is contested, with numerous studies providing evidence for and against the possibility.
The research undertaken at the NIH in Bethesda, Maryland, is based on extensive sampling and analysis of tissues taken during autopsies on 44 patients who died after contracting the coronavirus during the first year of the pandemic in the U.S.
The burden of infection outside the respiratory tract and time to viral clearance isn’t well characterized, particularly in the brain, wrote Daniel Chertow, who runs the NIH’s emerging pathogens section, and his colleagues.
The group detected persistent SARS-CoV-2 RNA in multiple parts of the body, including regions throughout the brain, for as long as 230 days following symptom onset. This may represent infection with a defective virus, which has been described in persistent infection with the measles virus, they said.
In contrast to other Covid autopsy research, the NIH team’s post-mortem tissue collection was more comprehensive and typically occurred within about a day of the patient’s death.
The NIH researchers also used a variety of tissue preservation techniques to detect and quantify viral levels, as well as grow the virus collected from multiple tissues, including lung, heart, small intestine, and adrenal gland from deceased Covid patients during their first week of illness.
“Our results collectively show that while the highest-burden of SARS-CoV-2 is in the airways and lung, the virus can disseminate early during infection and infect cells throughout the entire body, including widely throughout the brain,” the authors said.