Varicella zoster virus
Varicella zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or Human alphaherpesvirus 3 (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting children and young adults, and shingles (herpes zoster) in adults but rarely in children. As a late complication of VZV infection, Ramsay Hunt syndrome type 2 may develop in rare cases. VZV infections are species-specific to humans. The virus can survive in external environments for a few hours.[3]
VZV multiplies in the tonsils, and causes a wide variety of symptoms. Similar to the herpes simplex viruses, after primary infection with VZV (chickenpox), the virus lies dormant in neurons, including the cranial nerve ganglia, dorsal root ganglia, and autonomic ganglia. Many years after the person has recovered from initial chickenpox infection, VZV can reactivate to cause shingles.[4]
Morphology[edit]
VZV is closely related to the herpes simplex viruses (HSV), sharing much genome homology. The known envelope glycoproteins (gB, gC, gE, gH, gI, gK, gL) correspond with those in HSV; however, there is no equivalent of the HSV gD protein. VZV also fails to produce the LAT (latency-associated transcripts) that play an important role in establishing HSV latency (herpes simplex virus).[12] VZV virions are spherical and 180–200 nm in diameter. Their lipid envelope encloses the 100 nm nucleocapsid of 162 hexameric and pentameric capsomeres arranged in an icosahedral form. Its DNA is a single, linear, double-stranded molecule, 125,000 nt long. The capsid is surrounded by loosely associated proteins known collectively as the tegument; many of these proteins play critical roles in initiating the process of virus reproduction in the infected cell. The tegument is in turn covered by a lipid envelope studded with glycoproteins that are displayed on the exterior of the virion, each approximately 8 nm long.[13]
Treatment[edit]
Within the human body it can be treated by a number of drugs and therapeutic agents including acyclovir for chickenpox, famciclovir, valaciclovir for the shingles, zoster-immune globulin (ZIG), and vidarabine.[21] Acyclovir is frequently used as the drug of choice in primary VZV infections, and beginning its administration early can significantly shorten the duration of any symptoms. However, reaching an effective serum concentration of acyclovir typically requires intravenous administration, making its use more difficult outside of a hospital.[22]
History[edit]
Chickenpox-like rashes were recognized and described by ancient civilizations; the relationship between zoster and chickenpox was not realized until 1888.[29] In 1943, the similarity between virus particles isolated from the lesions of zoster and those from chickenpox was noted.[30] In 1974 the first chickenpox vaccine was introduced.[31]
The varicella zoster virus was first isolated by Evelyn Nicol while she was working at Cleveland City Hospital.[32] Thomas Huckle Weller also isolated the virus and found evidence that the same virus was responsible for both chickenpox and herpes zoster.[33]
The etymology of the name of the virus comes from the two diseases it causes, varicella and herpes zoster. The word varicella is possibly derived from variola, a term for smallpox coined by Rudolph Augustin Vogel in 1764.[34]