How do varicella (chickenpox) and herpes zoster (shingles) differ in presentation, diagnosis, treatment, and prevention?

Varicella vs Zoster: Key Differences

Varicella (chickenpox) and herpes zoster (shingles) are two distinct clinical manifestations of the same virus—varicella-zoster virus (VZV)—with varicella representing primary infection and zoster representing reactivation of latent virus from dorsal root ganglia. 1, 2, 3

Pathophysiology and Relationship

• Varicella occurs as the primary infection when VZV first enters a susceptible host through the upper respiratory tract or conjunctivae, typically during childhood 1, 3
• After primary varicella infection, VZV establishes lifelong latency in neuronal ganglia (dorsal root and cranial nerve ganglia), where it remains dormant for years to decades 1, 2, 3
• Herpes zoster results from reactivation of this latent virus, typically triggered by declining cell-mediated immunity associated with aging or immunosuppression 1, 2, 3
• Approximately 20-30% of people develop herpes zoster over their lifetime, with incidence increasing markedly after age 50 1, 4

Clinical Presentation

Varicella (Chickenpox)

• Presents with generalized vesicular rash in multiple stages of development (macules, papules, vesicles, pustules, and scabs occurring simultaneously) after a 14-16 day incubation period (range 10-21 days) 1
• Rash is more concentrated on the trunk and head than extremities, with most children developing 250-500 skin lesions 1, 4
• Accompanied by fever lasting approximately 5 days, with lesions frequently developing in the mouth, conjunctivae, or other mucosal sites 1
• Bilateral and diffuse distribution across multiple body regions 1, 5
• Patient is contagious from 1-2 days before rash onset until all lesions are crusted 1, 6

Herpes Zoster (Shingles)

• Presents as unilateral vesicular eruption following a dermatomal distribution along a single dermatome or adjacent dermatomes 1, 7, 4
• Prodromal pain typically precedes the rash by 24-72 hours in the affected dermatome 7
• Rash progresses through stages but remains localized to the affected dermatome(s) 1, 7
• May present with distinctive pseudodendritic (non-excavated) epithelial keratitis when involving the ophthalmic division of the trigeminal nerve 1
• Patient is contagious from 1-2 days before rash onset until all lesions have dried and crusted (typically 4-7 days after rash onset) 6

Diagnosis

Varicella

• Clinical diagnosis is typically sufficient in immunocompetent patients with the characteristic generalized vesicular rash in multiple stages 1, 5
• Laboratory confirmation is needed for immunocompromised patients or atypical presentations 7
• Serology (VZV IgG) is useful for determining susceptibility in uncertain cases, though history of chickenpox is 97-99% predictive of seropositivity in adults 1

Herpes Zoster

• Clinical diagnosis is based on unilateral dermatomal vesicular rash with characteristic pain 1, 7
• Serology is not useful for diagnosis of active shingles 1
• VZV DNA detection via nucleic acid amplification (PCR) from lesion material is highly specific and sensitive (approaching 100% for both) and can detect virus even in crusted lesions 1
• Tzanck smear or electron microscopy can detect multinucleate giant cells but cannot differentiate VZV from HSV 1

Treatment

Varicella

• Oral acyclovir is recommended for otherwise healthy adolescents and high-risk populations (immunocompromised children) when initiated early in the clinical course 8
• Intravenous acyclovir is indicated for severe or complicated varicella, particularly in immunocompromised patients 7, 8
• Treatment is most effective when initiated within 24 hours of rash onset 8
• Immunomodulator therapy should not be commenced during active chickenpox 1

Herpes Zoster

• Oral valacyclovir 1 gram three times daily or famciclovir 500 mg three times daily for 7-10 days is first-line treatment for uncomplicated herpes zoster in immunocompetent patients 7
• Acyclovir 800 mg orally five times daily for 7-10 days is an alternative but requires more frequent dosing 7
• Treatment should be initiated within 72 hours of rash onset for optimal efficacy in reducing acute pain, accelerating healing, and preventing postherpetic neuralgia 7
• Continue treatment until all lesions have completely scabbed, not just for an arbitrary 7-day period 7
• Intravenous acyclovir 10 mg/kg every 8 hours is required for disseminated or invasive herpes zoster, immunocompromised patients, or those with CNS/ophthalmic complications 7
• Topical antiviral therapy is substantially less effective than systemic therapy and is not recommended 7

Prevention

Varicella Prevention

• Two doses of live-attenuated varicella vaccine (Varivax) provide protection from severe chickenpox, given at 12-18 months and 4-6 years in countries with routine childhood vaccination 1
• Seronegative immunocompetent patients should receive two doses of varicella vaccine at least one month apart, completing the course at least 3 weeks before starting immunomodulators 1
• Varicella-zoster immune globulin (VZIG) should be administered within 96 hours (ideally within 10 days) after significant exposure for high-risk seronegative patients (immunosuppressed, pregnant women, premature infants) 1, 7
• If VZIG is unavailable or >96 hours have passed, a 7-day course of oral acyclovir beginning 7-10 days after exposure is recommended 7

Herpes Zoster Prevention

• The recombinant zoster vaccine (Shingrix) is recommended for all adults aged 50 years and older, regardless of prior herpes zoster episodes, providing >90% efficacy 7, 4
• Vaccination should ideally occur before initiating immunosuppressive therapies but can be given after recovery from acute episodes 7
• The live-attenuated vaccine (Zostavax) is contraindicated in immunocompromised patients due to risk of uncontrolled viral replication 7, 9

Complications and Special Populations

Varicella Complications

• Immunocompromised patients are at risk for severe or life-threatening disease, including pneumonia, hepatitis, encephalitis, or hemorrhagic disorders 1, 5
• Five of 20 reported cases of varicella in IBD patients proved fatal in one review 1
• Secondary bacterial infections, cerebellar ataxia, and Reye syndrome are recognized complications 5

Herpes Zoster Complications

• Postherpetic neuralgia is the major complication, with risk increasing with age 7, 9
• Immunocompromised patients have increased risk of dissemination (10-20% without prompt antiviral therapy), visceral involvement, and CNS disease 1, 7
• Ophthalmic zoster can cause keratitis, uveitis, retinitis, and vision-threatening complications 1, 7
• Ramsay Hunt syndrome (facial nerve involvement) can cause facial paralysis and hearing loss 7

Transmission and Infection Control

Varicella

• VZV is highly contagious with 80-90% of susceptible household contacts developing clinical infection 1
• Transmission occurs via direct contact, airborne droplets, or infected respiratory secretions 1, 6
• Airborne and contact precautions are required in healthcare settings until all lesions are crusted 6

Herpes Zoster

• Herpes zoster is approximately 20% as contagious as varicella and primarily spreads through direct contact with vesicular fluid 6
• Airborne transmission is possible but primarily documented in healthcare settings 6
• Standard and contact precautions with complete lesion coverage are sufficient for immunocompetent patients with localized disease 6
• Airborne and contact precautions are mandatory for disseminated zoster or immunocompromised patients until all lesions are dry and crusted 6
• A person with shingles cannot give another person shingles directly—they can only transmit VZV, causing chickenpox in susceptible individuals 6