Varicella-zoster virus

Background

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

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

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

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

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

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

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

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)

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

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

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

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