Varicella Zoster Causes, Varicella Zoster Effects, Varicella Zoster Symptoms, Varicella Zoster Diagnosis, Varicella Zoster Prognosis & Treatments

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Varicella Zoster

Definition

Q. What is Varicella Zoster?
Ans. Varicella zoster virus (VZV) is one of eight herpes viruses known to infect humans (and other vertebrates). It commonly causes chicken-pox in children and both shingles and postherpetic neuralgia in adults. 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 chickenpox (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 herpes zoster or shingles. Serious complications of shingles include postherpetic neuralgia, zoster multiplex, myelitis, herpes ophthalmicus, or zoster sine herpete.

Morphology

Morphology of Varicella Zoster
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 a icosahedral form. 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.

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 aciclovir, zoster-immune globulin (ZIG), and vidarabine.

Vaccine

Vaccine of Varicella Zoster
A live attenuated VZV Oka/Merck strain vaccine 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 FDA 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.

Treatment

Medical Care of Varicella Zoster

Treatment options are based on the patient's age, immune state, duration of symptoms, and presentation.
Several studies indicate that antiviral medications decrease the duration of symptoms and the likelihood of postherpetic neuralgia, especially when initiated within 2 days of the onset of rash. In typical cases that involve individuals who are otherwise healthy, oral acyclovir may be prescribed. An important study by Kubeyinje (1997) suggested that the use of acyclovir in healthy young adults with zoster is not clearly justified, especially in situations of limited economic resources.
Acyclovir has 2 limitations-bioavailability and the existence of some resistant strains of varicella-zoster virus (VZV).
Other medications, including valacyclovir, penciclovir, and famciclovir, are also available. They may have an increasing role in the treatment of typical zoster. Studies suggest that, when compared with oral acyclovir, the new medications may decrease the duration of the patient's pain.

Surgical Care of Varicella Zoster
Surgical care may be required for complications of zoster, such as necrotizing fasciitis.

Consultations

Consultation with a neurologist is indicated in cases of myelitis or encephalitis.
Consultation with an infectious disease specialist may be helpful if bacterial superinfection or viral resistance to acyclovir is evident.
Consultation with an ophthalmologist is indicated upon optic involvement.
Consultation with a dermatologist may be helpful when the rash is atypical.

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