Overview
Definition:
Varicella, commonly known as chickenpox, is a highly contagious viral infection caused by the varicella-zoster virus (VZV), a herpesvirus
It typically presents with a characteristic pruritic rash that progresses through vesicular, pustular, and crusted stages.
Epidemiology:
Varicella is endemic worldwide, with peak incidence in late winter and spring
It is most common in children aged 1-10 years, with nearly all individuals experiencing infection by adolescence
In unvaccinated populations, outbreaks are common in schools and daycares
The disease is less common but more severe in immunocompromised individuals and adults.
Clinical Significance:
While generally a mild illness in healthy children, varicella can lead to significant morbidity and mortality in immunocompromised individuals, pregnant women, and neonates
Complications include secondary bacterial infections, pneumonia, encephalitis, Reye's syndrome, and in rare cases, life-threatening disseminated varicella
Understanding acyclovir indications and post-exposure prophylaxis is crucial for preventing severe disease and its complications, particularly in vulnerable populations and for exam preparedness.
Clinical Presentation
Symptoms:
Prodromal symptoms in children are usually mild and include fever, malaise, anorexia, and headache
The characteristic rash typically begins on the trunk or face and spreads centrifugally to the limbs and mucous membranes
Lesions appear in crops and are described as "dewdrops on a rose petal." The rash is intensely pruritic
In adults, prodromal symptoms are more pronounced, and the disease can be more severe.
Signs:
The hallmark is the polymorphic rash in various stages of development simultaneously: erythematous macules, papules, vesicles, pustules, and crusts
Mucous membrane lesions (oral, conjunctival, genital) may be present
Lymphadenopathy can occur
Fever typically lasts 2-3 days, coinciding with the appearance of the rash.
Diagnostic Criteria:
Diagnosis is primarily clinical, based on the characteristic rash and epidemiological history
Laboratory confirmation is usually not required in immunocompetent individuals but may include viral detection via PCR from vesicular fluid or polymerase chain reaction (PCR) or serology (IgM/IgG antibodies) in complicated cases or for epidemiological surveillance
Definitive diagnosis involves isolation of VZV or detection of viral DNA.
Diagnostic Approach
History Taking:
Key questions include onset and progression of rash, presence of fever, pruritus, associated symptoms (cough, sore throat, neurological changes), vaccination status for varicella, history of contact with a varicella or herpes zoster case, and any underlying medical conditions (immunodeficiency, pregnancy, medications like steroids).
Physical Examination:
A thorough skin examination to assess the distribution, morphology, and stage of the rash (macules, papules, vesicles, pustules, crusts) is essential
Examine mucous membranes for lesions
Assess vital signs, hydration status, and look for signs of secondary bacterial infection or systemic complications.
Investigations:
Generally not needed for uncomplicated varicella in immunocompetent children
For severe, disseminated, or atypical cases, or in immunocompromised patients: PCR from vesicular fluid, throat swab, or blood for VZV DNA
Serology (IgM and IgG antibodies) can confirm recent infection but may be negative early in the illness
Tzanck smear can show multinucleated giant cells but is not VZV-specific.
Differential Diagnosis:
Other vesicular eruptions, including herpes simplex virus (HSV) infections, coxsackievirus infections (hand-foot-and-mouth disease, herpangina), molluscum contagiosum, impetigo, insect bites, and drug eruptions
Varicella-zoster virus (VZV) reactivation (herpes zoster) presents with a dermatomal rash.
Management
Initial Management:
For uncomplicated varicella in otherwise healthy children, management is primarily supportive
Focus on symptomatic relief, especially pruritus
Isolate the patient to prevent transmission until all lesions have crusted over (typically 5-7 days after rash onset).
Medical Management:
Antiviral therapy with oral acyclovir (5-20 mg/kg per dose, maximum 800 mg per dose, four times daily for 5-7 days) is recommended for individuals at high risk of moderate to severe disease or complications
This includes: immunocompromised patients, individuals with chronic skin or pulmonary conditions, those receiving chronic salicylate therapy (due to Reye's syndrome risk), and adults and adolescents with varicella
Therapy should be initiated within 24 hours of rash onset for maximal benefit
Intravenous acyclovir is indicated for severe disease, central nervous system involvement, or disseminated varicella.
Supportive Care:
Pruritus relief is crucial and can be managed with oral antihistamines (e.g., hydroxyzine, diphenhydramine), cool baths with colloidal oatmeal, and calamine lotion
Keep fingernails trimmed to minimize scratching and secondary bacterial infections
Encourage fluid intake and adequate rest
Acetaminophen can be used for fever
aspirin should be avoided due to the risk of Reye's syndrome.
Post Exposure Prophylaxis:
Post-exposure prophylaxis (PEP) with varicella-zoster immune globulin (VZIG) or varicella vaccine may be considered for susceptible individuals exposed to VZV
VZIG is indicated for immunocompromised individuals, pregnant women, and neonates born to mothers with varicella onset within 5 days before or 2 days after delivery
VZV vaccine can be given within 72 hours of exposure to immunocompetent individuals aged 12 months or older who have not had varicella or are unvaccinated
Vaccination may prevent or attenuate the disease.
Complications
Early Complications:
Secondary bacterial infections (e.g., impetigo, cellulitis, erysipelas, scarlet fever) are the most common complications, often caused by Streptococcus pyogenes or Staphylococcus aureus
Other serious complications include pneumonia (especially in adults), encephalitis, cerebellar ataxia, hepatitis, and acute arthritis.
Late Complications:
Postherpetic neuralgia (rare after primary varicella but a known complication of zoster)
Reye's syndrome is a rare but severe neurological disorder associated with aspirin use during VZV infection
Guillain-Barré syndrome can also occur.
Prevention Strategies:
The most effective prevention is varicella vaccination, which is highly effective in preventing infection or significantly reducing its severity
Strict adherence to isolation precautions until lesions crust
Judicious use of antivirals in high-risk individuals
Careful monitoring for signs of complications and prompt management
Avoidance of aspirin in children and adolescents with suspected varicella.
Prognosis
Factors Affecting Prognosis:
Prognosis is generally excellent in healthy children
Factors that worsen prognosis include advanced age (adults), pregnancy, immunocompromised status, and development of complications like pneumonia or encephalitis.
Outcomes:
Most healthy children recover fully within 1-2 weeks
Complications can lead to prolonged illness, hospitalization, and in rare instances, death
Immunocompromised individuals may experience severe, prolonged, or disseminated disease.
Follow Up:
Routine follow-up is not required for uncomplicated varicella in healthy children
Follow-up is indicated if complications arise or if the patient is immunocompromised to monitor recovery and assess for late sequelae
Patients receiving antiviral therapy should complete the full course as prescribed.
Key Points
Exam Focus:
Acyclovir indications: immunocompromised, adults, adolescents, chronic skin/lung disease, chronic salicylate use
Initiate within 24h of rash
VZIG/vaccine for post-exposure prophylaxis in specific high-risk groups
Avoid aspirin in children/adolescents
Secondary bacterial infections are common complications.
Clinical Pearls:
Remember the "dewdrops on a rose petal" description for the rash morphology
Pruritus management is key for patient comfort and preventing secondary infections
VZV can remain latent and reactivate as herpes zoster later in life
Vaccination is the cornerstone of primary prevention.
Common Mistakes:
Prescribing acyclovir for all varicella cases without considering risk factors
Delaying antiviral initiation beyond 24 hours
Using aspirin for fever management
Misdiagnosing vesicular rashes
Not considering isolation precautions, leading to nosocomial spread.