Post-viral fatigue is a fairly common occurrence following any type of viral infection. After a bout of flu or battling off an Epstein-Barr virus, many people find themselves experiencing persistent fatigue for a few weeks, or even months, after supposed recovery. Unpleasant as this prolonged experience is, most people can expect to make an eventual return to full health.
But for some patients the fog never lifts. Viral illnesses are thought to be one of the primary causes of myalgic encephalomyelitis (ME), aka chronic fatigue syndrome (CFS). This long-term condition is characterised primarily by extreme tiredness, along with brain fog, sore joints and flu-like symptoms.
Following the worldwide spread of Covid-19, around one in ten recovered patients are experiencing post-viral symptoms like these at least three months later, according to the UK Office for National Statistics. Many media reports and online support groups feature personal accounts of illness which carries on for much longer.
Christened ‘long Covid’, the condition appears to mirror post-viral ME in a number of ways and is distinct from the Covid-19 patients needing rehabilitative treatment for respiratory and cardiac damage caused by the virus.
“Any viral infection can cause a short-lived period of fatigue,” says ME Association medical adviser Dr Charles Shepherd. “That’s extremely common. What’s less common, but still reasonably so, is people who get a viral infection followed by post-viral fatigue syndrome, where you’ve got other symptoms like brain fog, feeling fluey, glands up, that sort of thing. That follows a lot of viral infections and goes on for a few weeks, and then people get over it and get better again.
“Then there’s the third group, where post-viral fatigue doesn’t resolve for three months or more and has a significant effect on what you can do – you can’t get back to work or normal life. At that point, most people would get a diagnosis of ME. That’s paralleling what’s happening for quite a few people with long Covid. There clearly is a lot of overlap between the two.”
ME has been historically neglected by clinicians and researchers
The sheer number of people now presenting with long Covid has forced clinicians and researchers to sit up and take notice of post-viral illness on a mass scale for the first time – something many ME patients have found frustrating after years of having their symptoms dismissed by doctors.
Shepherd says: “There’s still an awful lot of doctors out there who either don’t believe in ME or believe it’s all in the mind and are pretty dismissive and in some cases quite nasty to patients.”
Mindset coach Rachel was diagnosed with ME in 2008, but her doctors believe she has had the condition since 1998 when she was nine years old. She also has Ehlers Danlos syndrome and fibromyalgia.
Rachel says: “For years, I’d been told there was nothing wrong with me and it was all in my head. You do feel mental because there is no evidence to diagnose the condition, you can’t have a blood test, it’s a process of elimination.
“My GP turned around after diagnosis and said you can only have CFS for three years and then it becomes psychosomatic, and I went ‘oh great, that means I’m already psychosomatic then.’”
From 2006-2015 global research spending on ME averaged just $6.5m a year. This received a boost in 2017 when the US National Institutes of Health committed to doubling its spending in this area, allowing the figure to jump to $15m in 2017. When the US Centers for Disease Control (CDC) estimate that as many as 17 to 24 million people worldwide have ME the money being spent on the condition starts to look like small change.
Funding for long Covid research is surging
The $15m figure starts to look even slimmer when compared to the research funding now available for long Covid. In the UK alone, the National Institute for Health Research and UK Research and Innovation have funded four studies to address the long term physical and mental effects of Covid-19, for a total of £18.5m.
It’s not yet possible to say whether long Covid is clinically distinct from ME or simply the same condition arising en-masse from one clearly identifiable cause, warranting its own signifier. What is clear is that the significant overlap of symptoms mean a lot of long Covid research will have implications for the wider treatment of post-viral fatigue.
Marketing assistant Becky was diagnosed with ME 16 years ago, and also has EDS, postural tachycardia syndrome, asthma and interstitial cystitis.
“For me personally there’s a deep sadness, a sort of grief, about what could happen in terms of research or treatment options,” she says. “I’m happy that maybe this is the turning point for the condition, options will be available and hopefully one day soon people won’t have to be forgotten, but at the same time, I find it strangely upsetting that I never had that opportunity.
“I think a lot of people in the chronic illness community feel this way; it’s almost guilt for feeling that way as well, but it’s hard not to feel some level of resentment.”
An overactive immune system could be the cause of post-viral illness
There’s currently no universally accepted explanation for why viral illnesses, Covid-19 included, can trigger these long-term symptoms.
Shepherd says: “Because ME is a multi-system disease and there are these various different pathological tracks going on within it, there are different therapeutic interventions going on in relation to the different components of it.”
Some clinicians think CFS could be the result of an overactive immune system failing to switch itself off again once it has fought off an infection, leading to increased levels of chemicals called cytokines. There continue to produce symptoms of illness even though no pathogen is present.
“There’s quite a lot of emerging evidence of a range of dysfunction across the whole immune system orchestra, but in particular the role of cytokines. This may link in with some of the neuroimaging findings on what we call neuroinflammation,” says Shepherd. “This has led to various small studies as to whether drugs which can dampen down this type of immune system activation could be of help in people with ME and long Covid.”
Dr Raymond Perrin takes an osteopathic approach to CFS, attributing the symptoms of CFS to a build-up of lymph in the recently-described glymphatic system, a pseudolymphatic system in the brain and that plays an important role in the removal of interstitial metabolic waste products.
“It’s literally manually pushing the lymph out using certain techniques,” he says. “It’s cytokines, large protein molecules, that need to drain away. If they’re not draining properly the whole control mechanism drains backwards instead of forwards and you end up with a build-up of inflammatory toxins in the brain.”
Perrin, who has detailed these methods in his book The Perrin Technique, has been treating patients with ME and fibromyalgia in this way for 30 years and has been treating long Covid patients in the same way since last year.
Histamine and mitochondrial dysfunction could also be to blame
Long Covid and ME could also be down to something known as mass cell activation syndrome, where infections can destabilise the mass cells where histamine is produced. This could explain the allergy-type symptoms like rashes and hives experienced by some long Covid patients.
There is also evidence of mitochondrial dysfunction in people with CFS.
“Mitochondria are sort of the Duracell batteries within muscle cells that are where energy is produced,” says Shepherd.
“We’ve now got quite a lot of evidence showing that there’s a defect in metabolic energy production at a cellular level in people with ME, so there is a biochemical explanation for the fatigue that is going on.
“Whether there’s mitochondrial dysfunction going on in long Covid I don’t know, because no one’s really had the time of the opportunity to study it, but it’s certainly another possibility for therapeutic intervention.”
Could the attention given to long Covid improve things for ME too?
Fortunately, research into the causes and corresponding treatments for long Covid is moving very fast, as is recognition and acceptance of the condition.
Shepherd says: “Although there’s all this great overlap between ME/CFS and long Covid there’s been a great reluctance in the long Covid patient community especially, especially among doctors involved in its treatment, to actually accept this overlap. They don’t want long Covid people to just get landed with all the problems people with ME have had with recognition.
“There’s this sort of tension between the two communities, a lot of quite understandable anger if you look on social media. People are constantly saying ‘look, we’ve been living with an illness like long Covid for 30 years and no one’s taken us seriously’, and now there’s all this money ploughed into research and all these clinics set up overnight.”
Nonetheless, a step in the right direction is a step in the right direction, even when some patients may feel it’s too little too late.
Shepherd says: “As time goes on there’s going to be much more acceptance about this overlap between the two conditions. It may well be that some of these long Covid clinics, once they’ve got a component that deals with Covid-type symptoms, are more help by becoming an ME/CFS service than they are a service primarily dealing with people who have long term respiratory and cardiac problems.”