Herpes, according to a 2009 article in the journal "Antiviral Therapy," is a family of viruses that includes herpes simplex-1, herpes simplex-2, varicella zoster (shingles), herpes B, Epstein-Barr and other viruses. The viruses share several common characteristics.
Structure
According to "Harrison's Principles of Internal Medicine," herpes viruses are all members of the family "herpesviridae." Viruses can be double-stranded or single-stranded, composed of DNA or RNA. All herpesviridae are double-stranded DNA viruses. They are enclosed in a protein shell called a "capsid" that is further enveloped by a lipid bilayer that resembles the cell membrane of human mucous membranes, thus explaining the viruses' affinity for these tissues. In terms of shape and size, herpesviridae are 20-sided, symmetrical polygons (icosahedron) with a total diameter of about 180 to 200 nanometers (0.00000018-0.0000002 meters.)
Life Cycle
In most cells, herpesviridae are "lytic," which means that after the virus has replicated inside the cell, it destroys it. The exception to this, according to "Harrison's Principles of Internal Medicine," is neuronal cells or neurons, the cells that make up nerves. Herpesviridae can remain dormant in neurons for a person's entire lifetime, accounting for the episodic presentation that is characteristic of all herpes viruses. Periodically, by mechanisms that are not well understood, the virus is reactivated in some neurons, resulting in symptoms. Meanwhile, it remains dormant in others and "lives to fight another day."
Spectrum of Disease
Not surprisingly, the clinical manifestations of herpesviridae are also similar. First, all herpesviridae are associated with skin lesions. Second, reactivation of each virus results in a prodrome, or initial period of less severe, often flu-like symptoms preceding the full-blown disease. This is related to the interval between when the virus "reawakens" in the neurons to the time when it has spread sufficiently to other tissues to produce the full-blown disease. Third, because they live in the cells of the nervous system, herpesviridae are among the most common causes of central nervous system infections in humans, according to a February 2008 article in "Neuroimaging Clinics in North America." As the authors note, all herpes viruses can produce central nervous system disease, such as encephalomyelitis, meningitis or myelitis, which is often severe.
References
- "Antiviral Therapy"; Herpesviridae and Novel Inhibitors; G. Siakallis, D.A. Spandidos, G. Sourvinos; August 2009
- "Harrison's Principles of Internal Medicine, 17th edition"; A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longer, J.L. Jameson and J. Loscalzo; 2008
- "Neuroimaging Clinics of North America"; Central Nervous System Infections of Herpesvirus Family; N. Bulakbasi and M. Kocaoglu; February 2008
