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The coronavirus can damage lungs so severely that a transplant is a patient’s “only hope”, scientists have said.
Early research suggests the infection is mild in four out of five cases, however, it can trigger an inflammatory disease called COVID-19.
Scientists from the Northwestern Memorial Hospital in Chicago analysed discarded lung tissue from severely-ill patients who had a lung transplant, as well as those who died with the disease.
Results suggest the coronavirus can destroy the “fundamental framework” of the lungs, leaving the organs unable to recover.
In these extreme cases, a lung transplant is “the only hope for survival”, according to the scientists.
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Eight COVID-19 patients have undergone a double-lung transplant at Northwestern Medicine, which the Memorial Hospital is part of, to date – said to be the most performed by any health system in the world.
After receiving new lungs, patients tend to recover rapidly, added the team.
“We provide explicit evidence COVID-19 can cause permanent damage to the lung in some patients for whom lung transplantation is the only hope for survival,” said lead author Dr Ankit Bharat.
However, Dr Len Horovitz, from Lenox Hill Hospital in New York City, stressed the extreme procedure is “reserved for very few patients”.
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Lung transplants are generally considered safe, however, they can come with side effects.
“Complications of transplants include infection (possibly even with COVID-19 again), bacterial infection and possible rejection of the transplanted lungs,” said Dr Horovitz.
In some cases ‘the only option is replacement’
After analysing the critically-ill and deceased COVID patients, the scientists found so-called KRT17 cells in the lung tissue of those with irreversible damage.
The same cells have also been found in patients with end-stage pulmonary fibrosis, the medical term for lung scarring.
“As in pulmonary fibrosis, we found COVID-19 led to the recruitment of circulating immune cells called monocytes, which are likely recruited to the lung to kill the virus,” said co-author Dr Scott Budinger.
“In the fibrotic lung, these cells also promote the formation of fibrotic scar tissue.
“These cells can be easily and safely sampled, and might also help mark patients who are failing to recover from COVID-19.”
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The same cells may also be responsible for the breakdown of the lungs’ framework.
“The progenitor cells [basic cells that can become more specialised] in the lungs necessary for healing can repopulate wounds of the lung by moving along the basic underlying framework of the lung matrix,” said Dr Bharat.
“When the framework is destroyed, the progenitor cells have no place to go and lungs develop large holes that serve to harbour infections, an observation we also made during the tough transplant surgeries in these patients.
“Think of it this way; after an earthquake, if the basic structure of a building survives, it can still be refurbished. However, if it is levelled, the only option is replacement.”
In better news, the coronavirus has not returned in the Northwestern patients who have had a lung transplant to date.
This is despite immune-suppressing drugs being administered to reduce the risk the donor organs will be rejected.
The scientists also found patients can be placed on extracorporeal membrane oxygenation (ECMO), life support that acts like the heart and lungs, while they await a transplant.
Northwestern’s most recent transplant took place on Thanksgiving in a patient who had spent 130 days on ECMO, the longest known time in the world before receiving a transplant.
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‘You can’t even distinguish it used to be a lung’
This is not the first time experts have flagged how the coronavirus can impact lung structure.
Most of the victims were found to have “extensive lung damage” caused by a “profound disruption of the normal lung structure”.
Almost nine in 10 also had abnormally large cells caused by the fusion of several smaller ones, which could have led to dangerous inflammation and blood clots.
In June, doctors told the BBC tens of thousands of survivors will need to be recalled to check for pulmonary fibrosis.
“In the six-week scans we're seeing so far, I would say between 20% and 30% of patients who have been in hospital appear to show some early signs of lung scarring,” said Dr Sam Hare, from the British Society of Thoracic Imaging.
Professor Mauro Giacca, from the University Hospital of Trieste, previously told parliament the lungs of some coronavirus victims were completely unrecognisable.
The deceased, who were in hospital for more than a month, had “complete disruption of the lung architecture”, he added.
“In some lights you can’t even distinguish it used to be a lung.”
The coronavirus is one of seven strains of a virus class that are known to infect humans.
Others include severe acute respiratory syndrome (Sars) and Middle East respiratory syndrome (Mers), which killed 774 and 858 people in 2002/3 and 2012, respectively.
Between 20% and 60% of Sars and Mers survivors are said to have experienced a health problem similar to pulmonary fibrosis.
A 15-year follow-up study by scientists from Peking University People’s Hospital in Beijing found this generally eased over time.
“My concern with COVID-19 is so much [more] of the population has been infected [than with Sars or Mers]”, said Dr Hare.
Since the outbreak was identified, more than 63 million coronavirus cases have been confirmed worldwide.
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