Now researchers believe those with long Covid could benefit from a co-ordinated treatment strategy.
Lead author and University of Otago biochemistry researcher Emeritus Prof Warren Tate said the research was the first comparative molecular study of the immune cell proteins of both conditions, and it "strongly affirms" the link between the two.
"This means information from study of the pathophysiology of ME/CFS and therapeutic opportunities that have slowly accumulated over the last 30 years can be transferred to understanding and treating the now estimated 100 million cases of long Covid worldwide.
"But equally important, the immense resources put into long Covid research currently in the rich nations, while yet to produce major breakthroughs, can also benefit the many millions of ‘hidden’ ME/CFS patients, whose numbers have increased steadily over time in the absence of their recovery from the illness."
Data gathered from six long Covid patients was found to be similar to data gathered from nine diagnosed ME/CFS patients, who had had the condition for 16 years on average.
In susceptible people, the normal transitory immune/inflammatory response of the peripheral nervous system to infection or stress did not resolve quickly as in most people, he said.
Instead, it became chronic and led to a cascade effect involving the brain, immune system and central nervous system, which in turn resulted in multiple neurological symptoms and poor brain regulation of body physiology.
"It highlights within our community there are significant numbers of people debilitated now with disrupted immune systems, dysfunctional energy production and disturbed brain regulation of their overall physiology that severely disrupts their family lives, ability to work and participate in their communities long term, and that these people need support from all levels of society."
Therapeutic targeting of the immune response/inflammatory pathways could be effective, he said.
While potential compounds were available that targeted different points of the cellular energy production pathway, no systematic studies had been carried out to determine whether they showed real benefit.
Investment in combined clinical trials to treat both conditions was desperately needed, he said.
"Immunotherapy for treating specific features of a disturbed immune system for many diseases is in a revolutionary phase of development and should have potential for application to ME/CFS and long Covid patients, now the specific changes in their dysfunctional immune systems are being carefully documented."
He called for national guidelines with best-practice disease management plans for clinicians, so both patient groups would have a good chance of a more fulfilling life, no matter the stage of their illness.
Although he pointed out this must be accompanied by specialist clinics with a range of practitioners to support the patient’s needs.
