Human herpesviruses (HHVs) are large, double-stranded DNA viruses belonging to the Herpesviridae family. They share a conserved genomic architecture and lifecycle, characterized by two key phases: lytic replication, where the virus actively replicates and produces new virions, and latency, a dormant state within host cells that can later reactivate. Their ~125–240 kb genomes encode dozens to hundreds of proteins, including viral enzymes (e.g., DNA polymerase), tegument proteins, and immune evasion factors. HHVs infect a wide range of cell types and establish life-long infections, with reactivation often triggered by stress or immune suppression.
Out of more than 130 known herpesviruses, nine are known to primarily infect humans, including:
- Herpes simplex 1 and 2 (HSV-1 and HSV-2) - HSV-1 typically causes cold sores, while HSV-2 is primarily responsible for genital herpes.
- Varicella-zoster virus (VZV or HHV-3) - causes chickenpox and can later reactivate to cause shingles.
- Epstein-Barr virus (EBV or HHV-4) - Best known for causing infectious mononucleosis ("mono" or "glandular fever").
- Human cytomegalovirus (CMV or HHV-5) - Can cause serious complications in immunocompromised individuals and newborns.
- Human herpesvirus 6A and 6B (HHV-6A and HHV-6B) - Associated with roseola in infants and possibly linked to neurological conditions.
- Human herpesvirus 7 (HHV-7) - Similar to HHV-6, often acquired in early childhood.
- Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8) - Linked to Kaposi's sarcoma, especially in individuals with weakened immune systems.
