Varicella Zoster Virus (VZV)
|Genome: DNA Virus, dsDNA Virus||Structure: Enveloped Virus, Icosahedral Virus|
- VZV is highly contagious and transmission is likely through respiratory secretions.
- The basic pathogenic stages of VZV are similar to those of HSV (See HSV page). Primary infection with VZV likely occurs following inoculation of the respiratory epithelium where the virus locally proliferates and then undergoes systemic dissemination through viremia. Symptomology of the primary infection, termed "Chickenpox", is a result of viremia and proliferation of the virus in the skin. Following the development of effective cell-mediated immunity, the virus remains latently infected in dorsal root ganglia]. Reactivation occurs when cell-mediated immunity wanes, often in the elderly, resulting in the syndrome of "Shingles".
- VZV can cause two basic syndromes known as "Chickenpox" and "Shingles". Chickenpox is typically observed in children and is the result of primary infection with the virus. Shingles is typically observed in the elderly due to waning cell-mediated immunity and represents localized reactivation of the virus.
- Chickenpox is characterized by constitutional symptoms along with a skin rash that typically begins on the trunk, spreads over the entire body, and may include mucous membranes such as the vagina, oral mucosa, and pharynx. Lesions are maculopapular or vesicular, may be clustered, and sit on an erythematous base.
- Shingles is characterized by development of highly painful chickenpox-like skin lesions unilateraly within a single dermatome representing the innervation pattern of a single dorsal root ganglion. Post-herpetc neuralgia can last for months after the reactivation clears, causing pain within the previously affected dermatome. When reactivation occurs from the trigeminal ganglion it follows the pattern of innervation of the trigeminal nerve, which can cause infection of the cornea, and consequently keratitis that can lead to blindness.
- VZV infection can result in potentially serious complications especially in immunocompromised patients with reduced cell-mediated immunity. These include varicella pneumonia, varicella encephalitis, and disseminated disease. For unknown reasons, varicella pneumonia occurs more frequently in immunocompetent adults, thus infection with VZV as a child is preferred.
- A live, attenuated VZV vaccine is now available and has significantly reduced the incidence of VZV infections.
- Treatment for VZV infection is largely supportive; however if infection is identified early, treatment with acyclovir or its newer analogs famciclovir or valacyclovir may be helpful.