Varicella zoster virus
Encyclopedia
Varicella zoster virus is one of eight herpes viruses
known to infect humans (and other vertebrates). It commonly causes chicken-pox in children and Herpes zoster (shingles)
in adults and rarely in children.
(varicella), which may rarely result in complications including encephalitis
or pneumonia
. Even when clinical symptoms of chickenpox have resolved, VZV remains dormant in the nervous system
of the infected person (virus latency
), in the trigeminal
and dorsal root ganglia
. In about 10–20% of cases, VZV reactivates later in life producing a disease known as shingles. Serious complications of shingles include postherpetic neuralgia
, zoster multiplex, myelitis, herpes ophthalmicus, or zoster sine herpete.
, valaciclovir for the shingles, zoster-immune globulin
(ZIG), and vidarabine
. VZV immune globulin
is also a treatment.
is available and is marketed in the United States under the trade name Varivax. It was developed by Merck, Sharp & Dohme
in the 1980s from the Oka strain virus isolated and attenuated by Michiaki Takahashi and colleagues in the 1970s. It was submitted to the U.S. Food and Drug Administration
for approval in 1990 and was approved in 1995. Since then, it has been added to the recommended vaccination schedules for children in Australia
, the United States
, and many other countries. Varicella vaccination has raised concerns in some that the immunity induced by the vaccine may not be lifelong, possibly leaving adults vulnerable to more severe disease as the immunity from their childhood immunization wanes. Vaccine coverage in the United States in the population recommended for vaccination is approaching 90%, with concomitant reductions in the incidence of varicella cases and hospitalizations and deaths due to VZV. So far, clinical data has proved that the vaccine is effective for over 10 years in preventing varicella infection in healthy individuals and when breakthrough infections do occur, illness is typically mild. In 2007, the ACIP recommended a second dose of vaccine before school entry to ensure the maintenance of high levels of varicella immunity.
In 2006, the United States Food and Drug Administration approved Zostavax
for the prevention of shingles. Zostavax is a more concentrated formulation of the Varivax vaccine, designed to elicit an immune response in older adults whose immunity to VZV wanes with advancing age.
Herpesviridae
The Herpesviridae are a large family of DNA viruses that cause diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word herpein , referring to the latent, recurring infections typical of this group of viruses...
known to infect humans (and other vertebrates). It commonly causes chicken-pox in children and Herpes zoster (shingles)
Herpes zoster
Herpes zoster , commonly known as shingles and also known as zona, is a viral disease characterized by a painful skin rash with blisters in a limited area on one side of the body, often in a stripe...
in adults and rarely in children.
Nomenclature
Varicella-zoster virus is known by many names, including: chickenpox virus, varicella virus, zoster virus, and human herpes virus type 3 (HHV-3).Human disease
Primary VZV infection results in chickenpoxChickenpox
Chickenpox or chicken pox is a highly contagious illness caused by primary infection with varicella zoster virus . It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring...
(varicella), which may rarely result in complications including encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
or pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
. Even when clinical symptoms of chickenpox have resolved, VZV remains dormant in the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
of the infected person (virus latency
Virus latency
Virus latency is the ability of a pathogenic virus to lie dormant within a cell, denoted as the lysogenic part of the viral life cycle. A latent viral infection is a type of persistent viral infection which is distinguished from a chronic viral infection...
), in the trigeminal
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
and dorsal root ganglia
Dorsal root ganglion
In anatomy and neuroscience, a dorsal root ganglion is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.-Unique unipolar structure:...
. In about 10–20% of cases, VZV reactivates later in life producing a disease known as shingles. Serious complications of shingles include postherpetic neuralgia
Postherpetic neuralgia
Postherpetic neuralgia is a neuralgia caused by the varicella zoster virus. Typically, the neuralgia is confined to a dermatomic area of the skin and follows an outbreak of herpes zoster in that same dermatomic area...
, zoster multiplex, myelitis, herpes ophthalmicus, or zoster sine herpete.
Morphology
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 HSV gD. VZV also fails to produce the LAT (latency-associated transcripts) that play an important role in establishing HSV latency (herpes simplex virus). VZV virons are spherical and 150–200 nm in diameter. Their lipid envelope encloses the nucleocapsid of 162 capsomeres arranged in an icosahedral form.[2] Its DNA is a single, linear, double-stranded molecule, 125,000 nt long. The capsid is surrounded by a number of 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.Treatment
The virus is very susceptible to disinfectants, notably sodium hypochlorite. Within the human body it can be treated by a number of drugs and therapeutic agents including acyclovir for the chicken pox, famciclovirFamciclovir
Famciclovir is a guanine analogue antiviral drug used for the treatment of various herpesvirus infections, most commonly for herpes zoster . It is a prodrug form of penciclovir with improved oral bioavailability...
, valaciclovir for the shingles, zoster-immune globulin
Zoster-immune globulin
Zoster-immune globulin is a globulin fraction of pooled plasma extracted from human donors who have recovered from infection by herpes zoster. ZIG is used in the prevention of chickenpox and shingles, but is not known to be useful in treating clinical varicella or zoster.- References :...
(ZIG), and vidarabine
Vidarabine
Vidarabine or adenine arabinoside is an antiviral drug which is active against herpes simplex and varicella zoster viruses.- How the drug was discovered :...
. VZV immune globulin
VZV immune globulin
VZV globulin is an immune system medication that is used mostly for immunosuppressed patients. It shortens the course of cutaneous disease and may protect against its dissemination. Varicella zoster virus is a virus in humans that causes chickenpox and shingles....
is also a treatment.
Vaccination
A live attenuated VZV Oka/Merck strain vaccineVaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
is available and is marketed in the United States under the trade name Varivax. It was developed by Merck, Sharp & Dohme
Merck & Co.
Merck & Co., Inc. , also known as Merck Sharp & Dohme or MSD outside the United States and Canada, is one of the largest pharmaceutical companies in the world. The Merck headquarters is located in Whitehouse Station, New Jersey, an unincorporated area in Readington Township...
in the 1980s from the Oka strain virus isolated and attenuated by Michiaki Takahashi and colleagues in the 1970s. It was submitted to the U.S. Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
for approval in 1990 and was approved in 1995. Since then, it has been added to the recommended vaccination schedules for children in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and many other countries. Varicella vaccination has raised concerns in some that the immunity induced by the vaccine may not be lifelong, possibly leaving adults vulnerable to more severe disease as the immunity from their childhood immunization wanes. Vaccine coverage in the United States in the population recommended for vaccination is approaching 90%, with concomitant reductions in the incidence of varicella cases and hospitalizations and deaths due to VZV. So far, clinical data has proved that the vaccine is effective for over 10 years in preventing varicella infection in healthy individuals and when breakthrough infections do occur, illness is typically mild. In 2007, the ACIP recommended a second dose of vaccine before school entry to ensure the maintenance of high levels of varicella immunity.
In 2006, the United States Food and Drug Administration approved Zostavax
Zostavax
Zostavax is a live vaccine developed by Merck & Co. which has been shown to reduce the incidence of herpes zoster by 51.3% in a study of 38,000 adults aged 60 and older who received the vaccine. The vaccine also reduced by 66.5% the number of cases of postherpetic neuralgia and reduced the...
for the prevention of shingles. Zostavax is a more concentrated formulation of the Varivax vaccine, designed to elicit an immune response in older adults whose immunity to VZV wanes with advancing age.