According to researchers from Linköping University COVID-19 can reactivate viruses that had become latent in cells, particularly in people with myalgic encephalomyelitis.
Severe, long-term fatigue, post-exertional malaise, pain, and sleep problems are all signs of myalgic encephalomyelitis, also known as chronic fatigue syndrome. The cause of the condition is still not fully understood, although it is known that in most cases the onset follows a viral or bacterial infection.
The health of myalgic encephalomyelitis is not restored even after the original infection is resolved. As the cause of the disease is not known no diagnostic tests have not been developed.
The researchers hope their findings will contribute new knowledge of the causes of the disease and improve the prospects of reaching a diagnosis.
The results have been published in the journal Frontiers in Immunology.
Dangerous viruses can lay dormant in the body
“This patient group has been neglected. Our study now shows that objective measurements are available that show physiological differences in the body’s reaction to viruses between myalgic encephalomyelitis patients and healthy controls,” said Anders Rosén, professor at the Department of Biomedical and Clinical Sciences at Linköping University, and leader of the study.
Based on previous studies, some researchers believe new infections can activate viruses that lie latent in the body’s cells after a previous infection. It has already been established that several herpes viruses can remain in a latent state in the body. Latent viruses can be reactivated many years after the initial infection and can cause a new bout of the disease.
However, scientists have found it difficult to determine whether these reactivated viruses are involved in myalgic encephalomyelitis. The COVID-19 pandemic gave the researchers an opportunity to study how myalgic encephalomyelitis affects people during mild virus infections.
The researchers studied 95 patients who had been diagnosed with myalgic encephalomyelitis and 110 healthy participants.
Each participant provided blood and saliva samples on four occasions during the study. These were tested for antibodies against COVID-19 and latent viruses. The researchers found antibodies against common herpes viruses in saliva, including Epstein-Barr virus (EBV), which infected nearly every participant.
How myalgic encephalomyelitis is reactivated
EBV is usually a mild infection, but sometimes the teenage years can develop glandular due to the virus. EBV remains in a latent condition in the body and can proliferate in situations in which the immune system is impaired, causing fatigue, and increased risk of lymphoma.
Around 50% of the participants were infected with COVID-19 during the first wave of the pandemic. In more than one-third of cases, the infection had been asymptomatic. After the infection had passed, however, the researchers were able to detect specific antibodies in the saliva that suggested that three latent viruses had been reactivated, one of these was EBV. The reactivation was seen both in patients with and without myalgic encephalomyelitis but was significantly stronger in those with the condition.
The researchers describe this as a domino effect as infection with a new virus activates other latent viruses in the body. They suggest that this process can cause a chain reaction with an elevated immune response. When this happens the immune system attacks certain tissues, such as nerve tissue, in the body.
Previous studies have found that the mitochondria that produce energy in the cells are affected, suppressing the metabolism of people with myalgic encephalomyelitis.
“Another important result from the study is that we see differences in antibodies against the reactivated viruses only in the saliva, not in the blood. This means that we should use saliva samples when investigating antibodies against latent viruses in the future,” explained Rosén.
The researchers believe their findings can contribute to developing immunological tests to diagnose myalgic encephalomyelitis and possibly also long COVID.
“We now want to continue and carry out more detailed investigations into the immune response in myalgic encephalomyelitis, and in this way understand the differences between the antibody responses against latent viruses,” said Eirini Apostolou, principal research engineer, and lead author of the study.