What are differences between herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2)?

Updated: Jul 17, 2018
  • Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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As noted (see Pathophysiology), HSE is caused by HSV, an enveloped, double-stranded DNA virus. HSV-1 and HSV-2 are both members of the larger human herpesvirus (HHV) family, which also includes varicella-zoster virus (VZV, or HHV-3) and cytomegalovirus (CMV, or HHV-5). HSV-1, or HHV-1, is the more common cause of adult encephalitis; it is responsible for virtually all cases in persons older than 3 months. HSV-2, or HHV-2, is responsible for a small number of cases, particularly in immunocompromised hosts.

HSV-1 causes oral lesions (so-called fever blisters); these are common and may respond to antiviral medications, though they spontaneously remit in most cases. HSV-2 causes genital lesions. It was previously thought to appear within 1-2 weeks of primary infection, then to recur with lessening severity. That lesions may appear clinically at any interval after primary infection is now known. HSV-2 may be treated with antiviral medications.

In adults, the host immune response, combined with viral factors, determines invasiveness and virulence. Mitchell et al showed that the invasiveness of HSV-1 glycoprotein variants is controlled by the host response. [17] Geiger et al used interferon-gamma–knockout mice to show how interferon-gamma protected against HSV-1–mediated neuronal death. [18] These data suggested that the presentation and severity of encephalitis vary. Recent research suggests that an inborn error of interferon-mediated immunity may predispose the HSV-1 infected individual to developing HSE. [19] Further support comes from additional research suggesting that specific interferon-beta production signaling pathways are important for the control of HSV replication in the brain. [20]

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