Daijiworld Media Network - New Delhi
New Delhi, Oct 13: Researchers have found that changes in the lung and mouth microbiomes are associated with severe long Covid symptoms, including breathing difficulties, cognitive problems and digestive issues, raising hopes of identifying new approaches to treating the condition.
The study suggests that differences in the microbes present in the respiratory system may help explain why some people develop more severe forms of long Covid. However, researchers cautioned that further studies are needed to establish whether these changes precede Covid-19 infection or occur as a consequence of it.
Dr Daniela Alferes de Lima Headley from the University of Dundee in the UK, the study's lead author, said millions of people worldwide continued to experience long Covid, while its underlying causes remained unclear.
"We know that millions of people worldwide are still affected by long Covid and its cause is still unknown. Long Covid affects multiple organs. The microbiome is important to maintain health throughout the body, so it is a strong candidate for something that may contribute to long Covid. Prior studies have shown some changes in the gut microbiome with long Covid, but Covid is a lung disease and so it makes sense to look to see if the lung microbiome is changed in long Covid," she said.
The research forms part of PHOSP-COVID, a major UK research programme jointly funded by the National Institute for Health and Care Research (NIHR) and UK Research and Innovation.
The study involved 771 people who had received treatment for Covid-19 at one of 38 UK hospitals between February 2020 and March 2021.
Researchers divided the participants into four groups based on the severity of their symptoms five months after hospital discharge. The categories were 'very severe', involving serious physical, mental and cognitive impairments; 'severe', involving serious mental and physical problems but no cognitive impairment; 'moderate', characterised primarily by cognitive difficulties; and 'mild', involving few symptoms and a good recovery.
Six months after discharge, researchers collected saliva samples to examine microbes in the mouth and sputum samples to analyse those in the lungs. DNA sequencing was used to identify the microbes present, assess their diversity and abundance, and compare the findings with participants' symptoms.
The results showed that people with very severe long Covid had marked differences in their oral and lung microbiomes compared with those who did not experience severe symptoms.
The researchers also identified associations between microbiome changes and specific health problems, including reduced lung function, neurocognitive symptoms and gastrointestinal issues.
Reduced lung function can affect the amount of air the lungs can hold or how easily air moves in and out. Neurocognitive symptoms include brain fog, memory problems, and difficulties with attention and concentration, while gastrointestinal symptoms include abdominal pain, nausea, diarrhoea and loss of appetite.
Among the changes associated with long Covid symptoms was an increased abundance of bacteria that produce lactic acid. These changes were also linked to signs of inflammation detected in patients' blood samples.
The study was led by Professor James Chalmers, Chair of Respiratory Research at the University of Dundee. He said patients who experienced the most severe symptoms five to six months after Covid-19 infection showed substantial changes in the microbes present in their mouths and lungs.
"People who had the worst symptoms five to six months after Covid infection had big changes in the microbiome in their mouth and lungs. We also found that changes in the airway microbiome were linked not just to lung problems, but also to symptoms like brain fog and gut symptoms, suggesting the lung microbiome could have effects on health more broadly," Chalmers said.
He added that researchers did not yet know whether the microbiome changes existed before infection or developed afterwards. It also remained unclear how the microbiome would change in subsequent years and whether the differences would gradually resolve.
"We urgently need to know what causes long Covid because it remains a major healthcare problem. Understanding what causes it could lead to better treatments; the microbiome can be changed using antibiotics, probiotics or other measures. We hope our findings will stimulate more research into long Covid and in the future, we would love to see treatment trials to help people with this devastating condition," he said.
PHOSP-COVID researchers are continuing to investigate the long-term effects of Covid-19 and approaches to managing the condition. Other areas of research include the role of inflammation in long Covid and potential treatments that could reverse it.
Professor Raquel Duarte, head of the European Respiratory Society's assembly on infectious diseases at the University of Porto in Portugal, who was not involved in the study, said millions of people worldwide continued to live with the disabling consequences of long Covid.
She noted that persistent respiratory, cognitive and other symptoms could affect people's ability to work, study and manage everyday activities, with wider consequences for families, healthcare services and society.
"Six years after the start of the pandemic, we still do not fully understand why some people develop long Covid or how best to support their recovery. This large, multicentre study identifies distinct patterns in the oral and airway microbiota of people with the most severe symptoms following hospitalisation for Covid-19," Duarte said.
She added that the findings were significant because the microbiome patterns were associated not only with respiratory impairment but also with cognitive and gastrointestinal symptoms.
"These findings provide an important basis for further longitudinal and mechanistic research. If these associations are confirmed, they may ultimately help us identify new ways to predict, prevent or treat the most disabling forms of long Covid," she said.