Varicella-zoster virus

Background

Microbiology

• dsDNA virus in the Alphaherpesvirus family, related to HSV
• Key glycoproteins
  • gB II target of neutralizing antibodies like VZIg
  • gC gp IV not essential
  • gE gp I binds Fc IgG
  • gH gp III fusion function
  • gL glycosylation

Epidemiology

• Varicella is more late winter or spring in temperate climates, often corresponds to school year
• Acquired by 5-10 years old in temperate climates
  • In tropical climates, more susceptibility in adults
• Incubation period is 21 days
• Infectiousness lasts from 24h before rash (around time of fever) to the final crusting
• Transmitted airborne, respiratory secretions; not transmitted on fomites

Pathophysiology

• Transmitted by respiratory route
• Primary viremia infects liver and RES (~14 days)
• Secondary viremia causes dissemination to skin

Clinical Presentation

Primary infection (varicella)

• Primary infection usually benign in childhood
• Primary infection can be severe in adolescents, adults, and immunocompromised hosts
• New vesicle formation stops within 4 days
• Presentation modified by prior vaccination
  • Less severe, fewer vesicles, less classic rash
• Vaccine-associated: can also get infected by the vaccine strain itself

Differential Diagnosis

• Enterovirus
• Staphylococcus aureus
• Drug reactions
• Contact dermatitits
• Eczema herpeticum
• Insect bites

Breakthrough

• 20% of vaccinated children still acquire varicella
• Milder, fewer sequelae

Sequelae

• SSTI: invasive GAS including nec fasc
• Hepatitis, especially in immunocompromised, transplant, and AIDS (can be severe)
• Diarrhea, pharyngitis, otitis, nephritis, transient arthritis, myocarditis, ...
• Neurologic
  • Acute cerebellar ataxia
  • Diffuse encephalitis
  • Aseptic meningitis, transverse myelitis, strokes
• Reye syndrome: vomiting, excitability, delirium, and coma
  • Secondary to varicella and concomitant aspirin
• Respiratory: pneumonitis can be severe
  • Typically develops days after rash
  • Consider acyclovir ± prednisone

High-risk populations

• Pregnancy
  • Spontaneous abortions, IUFD, prematurity
  • Congenital varicella syndrome
    • Highest risk <20 weeks
    • Cutaneous defects, cicatral scarring and limb atrophy
    • Microcephaly, autonomic dysfunction
  • If primary varicella 5 days before to 2 days after delivery, high risk of mortality
• Immune-compromised hosts
  • Can have progressive disease with prolonged lesions and multiorgan infection

Herpes zoster (shingles)

• Varicella reactivation from dorsal root ganglia
• Dermatomal
• Herpes ophthalmaticus (CN V1)
• Ramsay-Hunt syndrome
• Post-herpetic neuralgia

Risk factors

• Rising age predict zoster as well as postherpetic neuralgia
  • 50% by age 85 years
• Post-surgery
• HIV (even with normal CD4)
• Transplant (HSCT > SOT)

Immunocompromized

• May become disseminated
• Can become chronic with episodic viremia
• Prophylaxis
  • HSCT: prophylax with valacyclovir for 1+ year following transplant (longer if GVHD)
  • SOT: 3-6 mo after transplant and for duration of lymphodepletion

Diagnosis

• PCR most common, sensitive and specific, can be tissue, serum, CSF, saliva, etc
• Multinucleated giant cells on histology
• Cell culture
• Serology

Management

• Valacyclovir preferred to acyclovir
  • Main side effect of valacylovir is headache

Normal host

• Primary varicella
  • Simple VZV infection, start ASAP (<72 hours) after onset of rash if going to treat; or, don't treat
  • If higher risk or severe sequelae, more likely to treat
  • 5 days in normal host
• Zoster
  • Start treatment within 72 hours to reduce new lesions (doesn't affect PHN)

Immunocompromised host

• Primary varicella: start with IV acyclovir, then step down to oral valacyclovir
• Zoster: start with IV acyclovir, then PO with close followup, until no new lesions for 2 days (minimum 7 days)
• Pregnancy: treat zoster if more than 50 lesions
• Ophthalmic zoster should be treated (involve Ophtho)
• Acute retinal necrosis: IV acyclovir for 10 to 14 days, with steroids (involve Ophtho)
• Ramsay Hunt syndrome: PO antiviral with prednisone

Prevention

Post-exposure management

• Identify contacts: very long list, includes anyone with 5 minutes of face-to-face time, adjacent rooms or beds, ...
  • Infectious 1-2 days before onset of rash
• Isolation of contacts
  • Exposed patients without evidence of immunity should be discharge as soon as possible
  • If not discharged, isolate them starting 8 days from exposure (in airborne)
  • Duration of isolation 21 days; if VZIg (or IVIg), extend duration of isolation to 28 days
  • i.e. day 8 to 21 if no VZIg, day 8 to 28 if VZIg
• Post-exposure vaccination
  • Recommended for everyone, assuming that there is no documented immunity and there is no contraindication
  • Within 3-5 days post-exposure
• VZIg (or IVIg, if VZIg not available)
  • Indications
    • Immune-compromised without evidence of immunity
    • Pregnant woman without evidence of immunity
    • Child of mother she had primary chicken pox 5 days before to 2 days after delivery
    • Preterm >28 days without evidence of immunity
    • Preterm <28 weeks gestation
    • HSCT who have not had their vaccine post-transplant
  • Start within 10 days after exposure

Vaccination

Varicella

• Live attenuated varicella vaccine at 12 months then again at 4 to 6 years
• Can use for PEP if within 3 days of exposure to reduce severity and duration
• Live vaccine, so must be at least 12 months
• Two doses 90% effective, though can wane over time
• Adverse effects
  • Injection site reaction 20%
  • Rash with 2-5 lesions (1-3%) or generalized within 1 month (3-5%); it is infectious
  • Febrile seizures: MMR + VZV at 12 months has higher risk of febrile seizures
  • Disseminated, including meningitis
• See the Canadian Immunization Guide

Zoster

• Shingrix (non-live recombinant; 2 doses, 6 months apart; more effective) and Zostavax (live attenuated, 1 dose)
  • If Zostavax, give Shingrix after 7 years as a booster
  • If recent zoster, wait three years after an episode
  • Zostavax-induced immunity wanes fairly quickly while Shingrix-induced immunity appears to be much more durable
• Indicated in all people ≥50 years old to reduce risk of zoster and PHN
  • History of VZV or vaccination doesn't matter, everyone can get it
• See the Canadian Immunization Guide