Herpes Zoster: Cause and Treatment
Cause
Herpes zoster is caused by reactivation of varicella zoster virus (VZV) that remains dormant in the dorsal root ganglia or sensory ganglia of cranial nerves following primary varicella infection (chickenpox). 1
The reactivation occurs when cellular immune response fails to control latent VZV replication, typically in adults or elderly individuals. 1 The lifetime risk is 20-30% in the general population, with significantly increased risk in:
- Elderly patients - incidence rises sharply with age 1
- Immunocompromised hosts - including cancer patients, transplant recipients, HIV-infected individuals, and those on immunosuppressive therapies 1, 2
- Patients with specific comorbidities - diabetes mellitus, rheumatoid arthritis, cardiovascular disease, renal disease, systemic lupus erythematosus, and inflammatory bowel disease 1
Treatment
Antiviral Therapy: The Cornerstone
For immunocompetent adults with uncomplicated herpes zoster, oral antiviral therapy should be initiated within 72 hours of rash onset and continued until all lesions have scabbed. 2
First-Line Oral Options:
- Valacyclovir 1000 mg three times daily for 7-10 days 2
- Famciclovir 500 mg three times daily for 7 days 2, 3
- Acyclovir 800 mg five times daily for 7-10 days 2
Valacyclovir and famciclovir offer superior bioavailability and less frequent dosing compared to acyclovir, potentially improving adherence. 2 Treatment is most effective within 48 hours but should still be initiated up to 72 hours after rash onset. 2
Critical endpoint: Continue treatment until ALL lesions have completely scabbed, not just for an arbitrary 7-day period. 2 If lesions remain active beyond 7 days, extend antiviral therapy accordingly. 2
Intravenous Therapy for High-Risk Patients
Immunocompromised patients and those with severe disease require intravenous acyclovir 10 mg/kg every 8 hours. 4, 2
Indications for IV therapy include:
- Disseminated herpes zoster (multi-dermatomal or visceral involvement) 2
- Facial/ophthalmic zoster with suspected CNS involvement 2
- Severely immunocompromised hosts (active chemotherapy, transplant recipients, advanced HIV) 2
- Chronic ulcerations with persistent viral replication 4
Continue IV acyclovir for minimum 7-10 days and until clinical resolution is achieved. 2 Consider temporary reduction in immunosuppressive medications when feasible. 2
Monitor renal function closely during IV therapy with dose adjustments for renal impairment. 2 Assess for thrombotic thrombocytopenic purpura/hemolytic uremic syndrome in immunocompromised patients receiving high-dose therapy. 2
Special Populations and Situations
Facial/Ophthalmic Involvement:
Requires urgent treatment due to risk of vision-threatening complications and cranial nerve involvement. 2 Initiate oral valacyclovir 1 gram three times daily or famciclovir 500 mg three times daily within 72 hours. 2 Consider IV acyclovir for complicated facial zoster with suspected CNS involvement or severe ophthalmic disease. 2
Elevation of affected areas promotes drainage, and keeping skin well-hydrated with emollients prevents dryness and cracking. 2
HIV-Infected Patients:
For recurrent orolabial or genital herpes, use famciclovir 500 mg twice daily for 7 days or higher oral acyclovir doses (up to 800 mg 5-6 times daily). 2, 3 Consider long-term acyclovir prophylaxis (400 mg 2-3 times daily) for HIV-positive patients. 2
Transplant Recipients:
Uncomplicated herpes zoster: oral acyclovir or valacyclovir 2 Disseminated or invasive disease: IV acyclovir with temporary reduction in immunosuppression 2
Adjunctive Therapies
Topical antiviral therapy is substantially less effective than systemic therapy and is NOT recommended. 2
Corticosteroids (prednisone) may be used as adjunctive therapy in select cases of severe, widespread shingles, but carry significant risks in elderly patients. 2 Avoid corticosteroids in immunocompromised patients due to increased risk of disseminated infection. 2
Prevention Strategies
Post-Exposure Prophylaxis:
Varicella zoster immunoglobulin (or IVIG) within 96 hours of exposure is recommended for varicella-susceptible patients exposed to active VZV infection. 2 If immunoglobulin is unavailable or >96 hours have passed, give 7-day course of oral acyclovir beginning 7-10 days after exposure. 2
Vaccination:
The recombinant zoster vaccine (Shingrix) is recommended for all adults aged 50 years and older, regardless of prior herpes zoster episodes. 1, 2 This is a 2-dose series that should ideally be administered before initiating immunosuppressive therapies. 1, 2 The vaccine can also be considered after recovery from acute herpes zoster to prevent future episodes. 2
For adults aged 18 years and older who are or will be immunocompromised, RZV is recommended. 1 The live attenuated vaccine (Zostavax) is contraindicated in immunocompromised individuals. 1
Infection Control
Patients with active herpes zoster must avoid contact with susceptible individuals (those without prior chickenpox or vaccination) until all lesions have crusted, as lesions can transmit VZV and cause varicella in susceptible contacts. 2
Common Pitfalls to Avoid
- Do not rely on arbitrary 7-day treatment duration - continue until all lesions scab 2
- Do not use topical antivirals as monotherapy - they are ineffective 2
- Do not delay treatment beyond 72 hours when possible - efficacy decreases significantly 2
- Do not use live zoster vaccine in immunocompromised patients - use recombinant vaccine only 1
- Do not underdose acyclovir - 400 mg TDS is insufficient for herpes zoster (appropriate only for HSV suppression) 2
- Monitor for acyclovir resistance if lesions persist despite adequate treatment 2