Viral infections can trigger other dormant, or latent viruses. For example, the herpesviruses HSV and CMV can be reactivated in patients with HIV, because their immune systems become compromised. Now research has shown that SARS-CoV-2, the virus that causes COVID-19, can reactivate latent viruses in cells that have previously been infected. This was aespecially an issue for people with chronic fatigue syndrome (ME/CFS). The findings have been reported in Frontiers in Immunology.
Myalgic encephalomyelitis/chronic fatigue syndrome, ME/CFS causes pain, sleep disturbances, post-exertional malaise, and severe, chronic fatigue. ME/CFS is now considered a symptom of long COVID. For many years, clinicians debated about whether the disorder was real, particularly because the causes are unknown and there are no diagnostic indicators. But research has shown that ME/CFS is a real disease; it often follows a bacterial or viral infection, and the health of the affected individual does not return after the infection is eliminated.
"This patient group has been neglected," noted study leader Anders Rosén, a professor emeritus at Linköping University. This work has now revealed differences between how ME patients and healthy controls react to viruses, said Rosén.
The pandemic gave researchers a chance to study how ME/CFS patients reacted to a viral infection compared to healthy individuals. The investigators enrolled 95 ME/CFS patients and 110 healthy people in the study, and obtained samples of blood and saliva four times during one year. The researchers looked for antibodies against latent viruses and SARS-CoV-2.
This work revealed an antibody fingerprint against common herpes viruses in saliva. One was Epstein-Barr virus (EBV), which almost everyone has been infected with at some point. While most people are infected during childhood and recover, it can cause mononucleosis in some people, who may carry it as a latent condition. When the immune system becomes weakened, EBV can reactivate to cause fatigue, and can also increase the risk of lymphoma.
About half of the study volunteers were infected with SARS-CoV-2 early on in the pandemic. Of those, 58 percent of ME/CFS patients and 41 percent of unaffected individuals got mild COVID-19 symptoms. Infections were asymptomatic in about one-third of cases, and may people had not been aware of their SARS-CoV-2 infection
Once SARS-CoV-2 infections resolved, antibodies were identified in saliva that showed there was a strong reactivation of latent viruses in both healthy people and ME/CFS patients, thought the viral reactivation was much stronger in ME/CFS patients.
This process may also cause an overactive immune response, noted the researchers, which could lead to other problems. Overactive immunity can destroy tissue or impair mitochondria, which may cause fatigue.
"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," Rosén added.
Rosén acknowledged that ME/CFS and long COVID are very similar. Brain fog and post-exertional malaise and seen in both, while disruptions of the senses of smell and taste, and lung impairments are also seen in long COVID.