Metagenomic Analysis of Blood Virome in Ischemic Stroke Reveals an Increase in Herpesvirus Transcripts and Host Immune Activation

Viral infections may play a role in stroke, with potential contributions to thrombosis and vasculopathy. Associations between stroke risk, influenza, and herpesviruses have been identified in epidemiological studies. However, our understanding regarding the full effects of viral interactions with the immune system and host tissues is still emerging. Evaluating the virome in stroke and vascular disease will provide insights that may aid in the prevention and treatment of stroke. In this study we evaluate the human virome in ischemic stroke. Methods Viruses were measured by total RNA sequencing of blood from 37 patients with ischemic stroke and 32 controls of similar age and vascular risk factor status. RNA reads were examined for viral RNAs using a global alignment platform and a database of human virus genomes. The relationship between the quantity of viral RNA and stroke is examined. Host gene expression following stroke is examined in relation to the presence of viral RNAs. Results Viral RNAs were detected in the blood samples of both ischemic stroke and control groups. Viral reads with a prevalence > 3% and raw counts > 2 were from a total of 6 viral families. This included several common human herpesviruses (HHVs), adenoviruses, and papillomaviruses, as well as human pegivirus, respiratory syncytial virus, and human endogenous retrovirus K (HERV-K). Combined, counts from HHVs were higher in stroke compared to control by a fold change of 2.13. Coinfection with multiple HHVs was more common in stroke, with a 1.23 fold increase in the number of detected herpesviruses. Reads from 2 viral genes were increased in stroke, UL95 from cytomegalovirus (CMV), and EBNA2 from Epstein-Barr virus (EBV). Genes associated with stroke, including apolipoprotein E (APOE), C3, platelet-derived growth factor (PDGF), and CXCL2 were differentially expressed in stroke samples which contained high counts of one or both of UL95 and EBNA2. Conclusion Viral RNAs from multiple families can be detected within the human blood virome. HHV transcripts were the most abundant of viral RNAs detected. Among stroke patients, HHV transcripts were more prevalent, with higher counts, and indicated a higher rate of coinfection with multiple HHV species. Expression of the EBV gene EBNA2 and the CMV gene UL95 may relate to changes in immune gene expression following stroke. Further evaluation is needed to determine the effects that the human virome have on stroke risk, immune response to stroke, and long-term outcome.