Varicella-Zoster Virus
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Introduction
Varicella-Zoster Virus (VZV), or chicken pox, is a highly infectious and symptomatic herpes virus.
The Case of...
A brief case (1-2 sentences) with 2-3 questions (no answers) to prompt thinking by students.
Epidemiology
Almost all children are infected by age 15 (ref).
96% of adults are immune (ref).
Classification and Characteristics
VSV is a herpes II virus.
Viral double stranded DNA gets incorporated into the host genome.
Transmission and Infection
Varciella is transmitted through airborne pathways, but also direct contact or droplets.
It is very infectious - 90% of non-immune household contacts will become infected.
Patients are infectious from 24-48 hours before rash until all lesions are crusted over (5-7 days).
The incubation period is 10-21 days.
The virus replicates in throat, and subsequently spreads to skin, reticuloendothelial tissue and rarely lungs and brain.
The virus can remain latent in dorsal root and cranial nerve ganglia, reactivating later in life as shingles and affecting 10-20% of adults.
Maternal infection in 1st or 2nd trimester presents low risk of vertical transmission to the fetus, but can cause congenital varicella syndrome (low birth weight, CNS abnormalities, limb abnormalities, cutaneous scarring, eye lesions).
Infection 5 days before - 2 days following delivery can lead to severe neonatal disease.
Clinical Manifesations
Chicken Pox
Chicken pox generally characterized by fever and generalized vesicular eruption in a characteristic pattern. First a macule, papule, vesicle, pustule, ulcer, crust. The vesicle is described as a 'dew drop on a rose petal'.
The rash starts on trunk, then face, scalp, limbs, and mucosa, with an average of 500 lesions.
The rash is extremely itchy, and can also be accompanied by fever, malaise, and anorexia.
Adults can develop more severe disease, with pneumonia occurring in ~15% of adults.
Infections in immunocompromised patients or neonates can result in encephalitis, pneumonia, or disseminated infection.
Bacterial super-infection can occur due to S. aureus and Strep. pyogenes.
Congenital varicella syndrome can affect fetus if mother is non-immune.
Shingles
Shingles represents a reactivation of VSV, with migration from the dorsal root ganglion to the skin.
It is more common in middle ages to elderly patients or immunosuppressed people.
Shingles begins with a prodrome of itching or burning for 1-2 days. The rash is characterized by inflammation of sensory nerve and their ganglia, with a unilateral localized vesicular rash along one or more dermatomes.
Shingles lesions heal spontaneously in 2-3 weeks, but an intense post-herpetic neuralgia can remain.
complications of shingles can include:
Compications: 2-HAP-E
2e bacterial infection
Hepatitis
cerebellar Ataxia
Pneumonia
Encephalitis
- secondary bacterial infection (most common), with S. aureus or group A Streptococcus. This can result in impetigo, abscesses, cellulitis, necrotizing fasciitis, or sepsis.
- eye involvement (tip of the nose sign)
- cerebellar ataxia, pneumonia, hepatitis, encephalitis
- dissemination (immunosuppressed pt)
- post-herpetic neuralgia - usually over age 60, with pain and scarring: caused by damage to ganglionic neurons
Diagnosis
Chicken pox and shingles are both normally diagnosed clinically.
Serology can be used to determine immune status.
Methods of identifying the virus include:
- polymerase chain reaction (PCR)
- virus isolation allows for culture, though it is slow growing and cultures are often -ve
- electron microscopy
Treatment
Chicken Pox
Treatment is supportive, with acetaminophen, antipruritics.
**AVOID ASA due to threat of Reye's syndrome.
Discourage scratching and isolate patients until lesions are dry and crusted.
Acyclovir may be used in immunocompromised host and in pts with varicella pneumonia or CNS involvement
VZIG is post-exposure prophylaxis in immunocompromised or infected newborns.
Complications should be treated supportively.
Shingles
Antivirals may be used if diagnosis is made in the first 72 hrs, or if complcations are present.
Treat symptoms with compresses or analgesics. Often signficiant medical is required to control symptoms.
Resources and References
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