In this study, we aimed to explore if EBV reactivation associates with post-stroke fatigue. To our knowledge, this is the first study to examine EBV, and its relationship with fatigue, during stroke recovery. Here, we report a lack of evidence for EBV reactivation in people with post-stroke fatigue during chronic stroke recovery. However, we did see alterations in the antibody response to EBV in patients with high fatigue. There were no differences in total IgM or IgG antibody concentrations between high and low fatigue groups, suggesting this is specifically associated with the antibody response to EBV.
Estimates of EBV reactivation in the general population vary but have been reported between 30 and 50% (29–31), and reactivation is known to increase with age (32). In this study, we detected EBV in 25% of participants, indicating that people with a history of stroke may not have elevated EBV reactivation, although a direct comparison with healthy participants would be necessary to confirm. Increased IgG titres against EBV lytic antigen were shown to be a common feature in patients who experienced long-COVID, associated with high fatigue (5) and a smaller study confirmed reactivation of EBV in 50% of patients with long-COVID versus 20% with healthy recovery (33). However, in EBV reactivation was detected in 82% of patients admitted to the intensive care unit with ongoing severe COVID-19, suggesting peak viral reactivation occurs during acute illness (34). Further studies have confirmed that viral reactivation occurs during acute COVID-19 infection and is a predictor of long-COVID (35). Together, these studies suggest that sampling time is an important consideration when investigating EBV reactivation, but the immunological effects of this may persist beyond the reactivation event itself.
We examined EBV reactivation by measuring circulating virus and anti-EBV antibody titres and by both measures there was no evidence of EBV reactivation. Surprisingly, there were indications of an aberrant anti-EBV immune response in participants with high fatigue. The IgM titre against lytic EBV antigen, VCA, was decreased in participants with higher post-stroke fatigue and also negatively correlated with post-stroke fatigue. Additionally, a lower proportion of high fatigue participants were seropositive for the IgG titre against latency antigen EBNA1, however we did not observe a correlation with fatigue. The mechanism and clinical relevance of this finding is not clear from current data. Stroke induces a systemic suppression of immune response, the extent of which is associated with the initial stroke severity (36). We have previously shown that B cell numbers, and antibody responses, are reduced after moderate- severe stroke (18, 37). However, we saw no association between titres of anti-VCA IgM and infarct volume or stroke severity. Furthermore, there were no differences in total IgM or in CRP concentrations between low and high fatigue groups. This suggests that the altered antibody titres to EBV antigens is not simply a result of more extensive systemic immune alterations in the high fatigue patient group. We chose to examine patients at least five months (and up to eight years) post-stroke as fatigue is a chronic condition to examine if active EBV infection may drive fatigue. However, immune alterations that occur acutely after stroke are associated with increased infection risk. Therefore, it is possible that EBV reactivation could occur more acutely after stroke. The reduced antibody titres to EBV antigen in chronic recovery in high fatigue patients may be an indication of an aberrant immune response to earlier viral reactivation.
There are further limitations to consider in this study including the relatively small sample size. Additionally, fatigue is a subjective measure, reliant on patient reporting. In this study fatigue was examined by the FACIT-F tool, however various tools exist to measure fatigue and there can be discrepancies in the extent of fatigue recorded depending on which test is used (38). Here we examined only EBV, though there is evidence that other viruses reactivate following stroke, such as herpes zoster virus (20). Reactivation of multiple viruses, including cytomegalovirus and human herpesvirus (HHV) 6, HHV-7, HHV-8 have been associated with chronic fatigue and could play a role in fatigue after stroke (39).
Although we have not found an association with EBV reactivation during chronic stroke recovery and incidence of fatigue, the alterations to circulating EBV antibody titres suggest we should not fully dismiss a potential role for reactivation of EBV and/or other latent viruses in the pathophysiology of post-stroke fatigue. Further, larger studies using acute recovery timepoints and alternative latent viruses will be required to fully examine the role of viral reactivation in post-stroke fatigue.