Things to know about the root cause of chickenpox and shingles
Varicella zoster virus (also known as VZV or HHV-3) is a member of a large family of DNA viruses that cause infections and certain diseases in mammals, including humans. Taken together, they are known as herpesviruses, or Herpesviridae. More than 130 herpesviruses have been identified.
VZV is an exclusively human virus that is found worldwide and is highly infectious. The basic facts are that the primary VZV infection causes chickenpox, and then the virus goes dormant in the body. Years or even decades later it reactivates as shingles (herpes zoster, or HZ). But the virus’s backstory is an interesting one.
Here are 10 facts to know about VZV:
1. Herpesviridaederives from herpein, the Greek word meaning "to creep". This refers to the spreading cutaneous lesions associated with several herpes viruses, including herpes zoster.
2. There are 3 mammalian subfamilies known as Alpha-, Beta- and Gamma-herpesviridae. It is estimated that they arose approximately 180 to 220 million years ago. VZV belongs to the Alpha subfamily (Î±-herpesviruses) along with herpes simplex 1 and herpes simplex 2.1
3. The reproductive cycle of members of the alpha herpesvirus subfamily is very short, measured in hours. The viruses promptly destroy the host cell, are able to replicate in a wide variety of host tissues, and characteristically establish a latent infection in sensory nerve ganglia.
4. Herpesviruses do not survive long outside a host, so transmission usually requires close contact. For example, highly contagious chickenpox is usually transmitted from 1 person to another through direct contact with the blisters, saliva or mucus of the infected person. The virus can also be transmitted through the air by coughing and sneezing.
5. All herpesviruses can establish a latent infection within specific tissues that are unique for each virus. VZV establishes lifelong latency in cranial nerve and dorsal root ganglia.
6. Herpesviruses are genetically and structurally similar, but they cause an array of clinical syndromes that generally do not overlap. In the case of VZV, those syndromes are chickenpox and shingles.
7. VZV is among the 4 species of herpesviruses that are extremely widespread among humans and very adept at establishing lifelong infections. Ninety percent of adults are infected with at least 1. A latent form of the virus can live in their bodies for long periods of time without causing symptoms.
8. Chickenpox was not dependably distinguished from smallpox until the late 19th century. VZV was finally isolated from vesicular fluid of chickenpox and zoster lesions in 1954, leading ultimately to the varicella vaccine (Varivax) that was licensed for use in the United States in 1995. Two shingles vaccines are available to reduce the risk of herpes zoster.
9. Although the immunologic mechanism controlling the latency of VZV is not completely understood, factors associated with its reactivation are well documented. They include aging, immunosuppression, intrauterine exposure to VZV, and having had varicella at a young age (under 18 months).
10. A variety of adverse effects and co-conditions related to herpesviruses are currently being researched. Herpes zoster has been linked to Crohn disease and irritable bowel disease. It has also been identified as a risk factor for heart attack and stroke. Additionally, diabetes has been recognized as an independent risk factor for shingles and one of its most serious complications, postherpetic neuralgia.
1. McGeoch DJ, Cook S, Dolan A, et al. Molecular phylogeny and evolutionary timescale for the family of mammalian herpesviruses. Journal of Molecular Biology. 1995. https://doi.org/10.1006/jmbi.1995.0152