Myalgic encephalomyelitis (ME), also often known as chronic fatigue syndrome (CFS), already affects tens of millions of people worldwide. But according to new research, we could be facing twice as many cases in the near future.

A study from a team in Germany, published in Internal Medicine, says that the long-lasting effects of COVID-19 on many individuals will mean they could meet the diagnostic criteria for ME/CFS. While it's not yet clear if long COVID and ME/CFS are the same, they share enough similarities that mean ME/CFS case numbers could rise significantly in the coming years.

Clinically ME/CFS is defined as fatigue lasting at least six months, as well as intolerance to exercise. Yet until now there's been no reliable way of testing for the condition and its different presentations.

That's where a related study from experts at the Medical University of Vienna in Austria comes in. This second study has identified biomarkers in the blood that could be linked to ME/CFS – specific biological flags that tests can look out for.

"In our study, we see that the immunological evaluation of ME/CFS patients is of crucial importance," says immunologist Eva Untersmayr-Elsenhuber, from the Medical University of Vienna.

The biomarkers distinguished two different groups of people with ME/CFS in a sample of 39 adults: those with weakened immune systems, and those with issues with the lining of their intestines.

Both health complications have been previously linked to ME/CFS and long COVID without any clear conclusions on the nature of the relationship. In this case, immunodeficient patients showed reduced levels of a protein called C4a, while those without immunodeficiencies had gut problems and higher levels of the lipopolysaccharide binding protein (LBP).

For as long as ME/CFS has been investigated as a health condition, there have been questions on its potential links with viral infections. Though many with the condition can't readily recall a period of prior illness, a sizeable number develop their symptoms after succumbing to a virus, hinting at a potential cause.

"Patients suffering from immunodeficiencies are characterized by an altered innate immune function," says Untersmayr-Elsenhuber. "In ME/CFS patients with an intact immune system, the intestinal barrier function was reduced."

By testing for these proteins in the future, health professionals might be able to better understand some of the issues behind the ME/CFS diagnosis, and tailor treatments more specifically to individuals. It also enables researchers to take a closer look at the different variations of ME/CFS – those that might have been triggered by inflammatory responses and those that might have been triggered by problems with a leaky gut.

We're still a long way from properly understanding how ME/CFS starts or how to cure it, but it's progress. As long COVID continues to have a debilitating impact on tens of millions of people across the globe, sicknesses like ME/CFS that seem to be triggered by viruses may get worse before they get better.

"The use of standardized detection methods is needed to rapidly translate research into clinics," write the researchers in their published paper.

"This ensures the definition of bench-to-bedside orientated approaches to make evidence-based ME/CFS diagnosis and treatment generally available for patients."

The research has been published in the Journal of Clinical Medicine.