Epigenetic misprogramming of cell differentiation links transient viral infection to chronic diseases across tissues

Virus-induced epigenetic changes in stem-cell differentiation pathways emerge here as a shared mechanism linking fundamentally different chronic diseases, offering candidate biomarkers and new intervention targets. Chronic diseases increasingly trace back to transient viral exposure, yet unrelated pathologies also arise in tissues showing no signs of infection. Using Epstein-Barr virus (EBV), I show that different chronic EBV-associated diseases share epigenetic misprogramming within stem-cell differentiation hierarchies. These alterations propagate across diverse cell lineages, creating latent vulnerabilities unmasked by secondary insults. Breast cancer, long debated for possible EBV involvement, carries EBV-like methylation signatures in both precursor and invasive lesions, independent of lymphocytic infiltration. In multiple sclerosis, three independent cohorts (non-pathologic brain tissue, normal-appearing white matter, and blood) showed methylation abnormalities in the same stem-cell differentiation pathways disrupted in proven EBV-driven tumors and breast cancer. These findings identify virus-induced lineage misprogramming as an occult cross-disease mechanism supported by direct primary evidence.