The coronavirus that causes Covid-19 can spread within a few days from the respiratory tract to the heart, brain and almost every organ system in the body. It was found that sometimes the virus can persist in the body, even after a person's initial symptoms have subsided. A study found that the virus that has spread can last for months. Researchers at the United States National Institutes of Health conducted a comprehensive analysis of the distribution and persistence of the SARS-CoV-2 virus in the body and brain. It was revealed that the pathogen was able to replicate in human cells much longer. The research has been released online in a manuscript under review for publication in the journal Nature. The results show delays in clearing the virus as a potential contributor to persistent symptoms of COVID-19 sufferers. Understanding the virus' survival mechanisms, along with the body's response to any viral reservoir, helps improve care for sufferers.
“For a long time, we have been asking about the impact of Covid-19 on many organ systems. This paper explains why infection persists even in people who have mild or no acute symptoms,” said Director of the Center for Clinical Epidemiology in the St. Health Care System. Louis Ziyad Al-Aly.
However, the findings and techniques used in this study have not been reviewed by independent scientists and are mostly related to data collected from fatal Covid-19 cases, not patients with long-standing infection or so-called post-acute SARS-CoV-2 sequelae.
Controversial findings
The tendency of the corona virus to infect cells in the respiratory tract and lungs is still debated. Many studies provide evidence for and against the possibility that the coronavirus persists in the brain and liver. The study, conducted at the NIH in Bethesda, Maryland, was based on extensive tissue sampling and analysis taken during autopsies on 44 patients who died after contracting the coronavirus during the first year of the pandemic in the US. It was explained that the burden of infection outside the respiratory tract and the time required to clear the virus from infected tissue were not well characterized, particularly in the brain. Persistent SARS-CoV-2 RNA was detected in several parts of the body, including areas throughout the brain, for 230 days after the onset of symptoms. This likely indicates infection with defective viral particles, which has been described in persistent infection with the measles virus, the researchers explained.
"We don't fully understand the old Covid-19, but these changes could explain ongoing symptoms," said Raina MacIntyre, professor of global biosecurity at the University of New South Wales at Sydney, who was not involved in the study.
Researchers have not been able to predict the burden of chronic disease that will arise in the future. In contrast to other Covid-19 autopsy studies, the NIH team's post-mortem tissue collection is more comprehensive and usually occurs within about a day of the patient's death. The researchers also used various tissue preservation techniques to detect and measure virus levels, as well as grow virus collected from several tissues, including the lungs, heart, small intestine, and adrenal glands of Covid-19 patients who died during the first week of illness.
"Our results collectively suggest that while the highest burden of SARS-CoV-2 is in the respiratory tract and lungs, the virus can spread early during infection and infect cells throughout the body, including extensively throughout the brain," the authors said.
Viremic phase
The NIH researchers think that infection of the pulmonary system can result in an early viremic phase, in which the virus is present in the bloodstream and spreads throughout the body, even in patients who have mild or asymptomatic disorders. One of the patients in the autopsy study was a teenager who probably died of an unrelated seizure complication. This suggests infected children without severe Covid-19 may also develop systemic infections. Inefficient clearance of the virus in tissues outside the pulmonary system is likely related to a weak immune response outside the respiratory tract. Meanwhile, SARS-CoV-2 RNA was detected in the brains of six autopsy patients who died more than a month after developing symptoms, including one patient who died within 230 days of the onset of symptoms. Focusing on multiple brain areas is helpful in understanding neurocognitive impairment or brain fog and other neuropsychiatric manifestations of long-term Covid-19.
"We need to start thinking about SARS-CoV-2 as a systemic virus that may go away in some people, but in others it can persist for weeks or months and produce a long-lasting, multifaceted systemic disorder," he added.
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