Lung damage can shed light on “long-term COVID”.

Scientists who led the research said they also found some unique properties of SARS-CoV-2, the virus that causes COVID-19, which may explain why it can cause such harm.

“The results show that COVID-19 is not simply a disease caused by the death of virus-infected cells, but is likely the result of these abnormal cells that persist in the lungs for long periods of time,” said Mauro Giacca, professor at King’s College in London.

The researchers analyzed tissue samples from the lungs, heart, liver and kidneys from 41 patients who died of COVID-19 between February and April at the University of Trieste, Italy.

Giacca said while his team found no obvious signs of viral infection or persistent inflammation in any other organs, they discovered “a really big break in the architecture of the lungs” with healthy tissue “almost entirely replaced” by scar tissue.

“It could very well be considered that one of the reasons there are long-term COVID cases is because the lungs (tissues) are severely destroyed,” he said.

“Even if someone recovers from COVID, the damage caused can be massive.”

Growing evidence suggests that a small proportion of people who have had COVID-19 and have recovered can experience a range of persistent symptoms, including fatigue, brain fog, and shortness of breath.

The condition is known as long COVID.

According to Giacca, nearly 90 percent of the 41 patients had several characteristics unique to COVID-19 when compared to other forms of pneumonia.

One of these was extensive blood clotting of the pulmonary arteries and veins.

Another reason was that some lung cells were unusually large and had many nuclei – a result of the fusion of different cells into single large cells in a process known as syncytia.

The study, published in the journal Lancet eBioMedicine, also found that the virus was still present in many cell types.