Long Covid may be the body trying to fight off other viruses

Man wears face mask
Man wears face mask

Long Covid symptoms may be driven by the reactivation of dormant viruses such as herpes, scientists have suggested, after finding evidence of inflammation in the blood of sufferers.

At the last count by the Office for National Statistics (ONS) last year, some 1.9 million people reported symptoms of long Covid, which can include fatigue, brain fog and muscle aches.

Now Imperial College and the University of Leicester have found that in long Covid sufferers, the immune system is still active long after a Covid infection has cleared up, with tell-tale signs of inflammatory proteins detectable in the blood.

Experts said this inflammation might be caused by trace amounts of Covid-19 lingering in the body, auto-immunity, in which the immune system attacks the body’s own tissues, or even the reactivation of other viruses.

Dr Felicity Liew, from Imperial’s National Heart & Lung Institute, said: “Even though the acute phase of illness resolves, there may be virus persisting in the body that could continually trigger the immune system and cause the ongoing inflammation that we found.

“It can also cause reactivation of herpes viruses or people that previously had glandular fever caused by Epstein-Barr virus, and it can cause that to reactivate and cause ongoing symptoms.

“Or it can result in autoimmunity, and all of those scenarios result in the types of inflammation that we see, and could result in chronic and ongoing abnormal inflammation represented by these proteins highlighted here.”

Herpes viruses

There are eight herpes viruses that routinely infect humans, and which lie dormant in the body. Around 70 per cent of people in Britain carry the Herpes Simplex type 1 (HS1) virus, which causes cold sores, while 10 per cent have HS2, which can cause genital warts and is linked to cervical cancer.

Similarly, around nine in 10 people carry Epstein-Barr – also a type of herpes – which mostly causes no problems, but can sometimes lead to glandular fever, encephalitis, meningitis and trigger auto-immunity.

Usually dormant viruses are kept at bay by the immune system, but experts think Covid-19 requires so much attention that it may allow other viruses through the defensive cracks.

The new analysis looked at blood plasma from 426 people who had been hospitalised with Covid and had experienced long-term symptoms and compared them to blood from hospitalised people who had not had ongoing problems.

Those with long Covid showed cellular inflammation and activation of a family of immune system proteins called the “complement system”.

The complement system kicks in in response to infection or tissue damage and is known to be associated with many autoimmune and inflammatory conditions.

The research suggests that anti-inflammatory drugs, which help reset the body’s immune system could be helpful in treating long Covid.

Trial into Tocilizumab drug

The University of Leicester is leading a trial into the rheumatoid arthritis drug Tocilizumab, which lowers inflammatory proteins.

Researchers believe long Covid may be similar, or the same, as post-viral syndrome which leads to people experiencing fatigue and brain fog after influenza and other viruses, and may be to blame for conditions such as ME/CFS.

The team say the sheer number of people suffering ongoing symptoms after Covid gives the opportunity to get to the bottom of what is causing these after-viral effects, and could lead to help for other long-term conditions.

Chris Brightling, clinical professor in respiratory medicine at University of Leicester, who is leading trials into Tocilizumab, said: “I think we’re going to find commonalities and certain pathways across all post-viral syndromes although I would imagine that because each virus interacts with us differently the mechanism will be slightly different.

“I think it is very worthy of trying to understand mechanisms and Covid itself to try and understand new therapies. For many people who are still suffering.”

The team also found that certain long Covid symptoms were associated with specific immune signatures, with different proteins involved.

For example, people with gastrointestinal symptoms had increased levels of a marker called SCG3, which has previously been linked to impaired communication between the gut and the brain.

Professor Peter Openshaw, from Imperial’s National Heart & Lung Institute, lead investigator on the new study, said: “With one in 10 Sars-CoV-2 infections leading to long Covid and an estimated 65 million people around the world suffering from ongoing symptoms, we urgently need more research to understand this condition.

“At the moment, it’s very hard to diagnose and treat.

“This study, which includes detailed clinical data on symptoms and a raft of inflammatory blood plasma markers, is an important step forward and provides crucial insights into what causes long Covid.”

The study is published in the journal Nature Immunology.

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