Chickenpox

Chickenpox, also known as varicella, is a highly contagious viral illness caused by the varicella-zoster virus (VZV). It mainly affects children but can occur at any age. While usually mild in healthy individuals, it can lead to serious complications, particularly in adults, pregnant women, neonates, and immunocompromised individuals. Chickenpox is commonly recognised by its itchy, blister-like rash and is preventable through vaccination.

Causes

Chickenpox is caused by the varicella-zoster virus, a member of the herpesvirus family. The infection is primarily spread through respiratory droplets (coughing or sneezing) or direct contact with fluid from the blisters of an infected person. The virus is extremely contagious, with an incubation period of 10 to 21 days after exposure.

Pathophysiology

Following initial exposure, the virus enters the respiratory tract, replicates locally, and spreads via the bloodstream to the skin and other organs. The characteristic rash develops as a result of viral replication in the skin, forming vesicles filled with fluid. After resolution of the primary infection, the virus becomes dormant in the dorsal root ganglia. Reactivation of the virus later in life can lead to herpes zoster (shingles).

Signs and Symptoms

The classic presentation includes:

• Fever, malaise, and loss of appetite 1–2 days before rash
• Itchy rash that progresses from macules to papules, then vesicles, and finally crusts
• Rash typically begins on the face, chest, and back, then spreads
• Lesions are in various stages of healing simultaneously
• In adults, symptoms may be more severe, with higher fever and greater risk of complications

Risk Factors

• Being unvaccinated against varicella
• Close contact with an infected person
• Weakened immune system (e.g., HIV, cancer, immunosuppressive therapy)
• Pregnancy, particularly during the first and second trimesters
• Neonates born to mothers who develop chickenpox around the time of delivery
• Healthcare and childcare workers exposed to infected individuals

Investigation

Chickenpox is usually diagnosed clinically based on history and rash appearance. Laboratory tests may be required in uncertain cases or for high-risk individuals:

• PCR testing of lesion fluid for VZV DNA (most sensitive and specific)
• Direct fluorescent antibody test for VZV antigen
• Serological tests (VZV IgM and IgG) in suspected cases or immune status assessment
• Routine blood tests are generally unnecessary unless complications are suspected
• Imaging (e.g., chest X-ray) may be needed if pneumonia is suspected

Management

1. Non-Pharmacological Management

• Advise patients to rest and stay hydrated
• Cool baths and calamine lotion to relieve itching
• Keep fingernails short and clean to prevent scratching and secondary infection
• Isolate from school/work until all lesions are crusted over (usually 5–7 days)
• Educate parents and caregivers on hygiene and prevention of transmission

2. Pharmacological Management

• Antiviral therapy (e.g., aciclovir) is recommended in:
  1. Adults presenting within 24 hours of rash onset
  2. Immunocompromised individuals
  3. Pregnant women with chickenpox
  4. Neonates with perinatal exposure
• Antihistamines (e.g., chlorphenamine) to relieve itching
• Antipyretics such as paracetamol to manage fever (avoid aspirin due to risk of Reye’s syndrome)
• Varicella-zoster immune globulin (VZIG) may be given to high-risk contacts (e.g., immunocompromised, pregnant women) within 10 days of exposure

3. Surgical Management

Surgery is not a standard treatment for chickenpox. However, rare complications like abscess formation, necrotising fasciitis, or secondary bacterial infections may require surgical intervention and drainage.

Complications

While often mild in children, chickenpox can lead to:

• Secondary bacterial infections of the skin
• Pneumonia (especially in adults)
• Encephalitis or cerebellitis
• Reye’s syndrome (associated with aspirin use in children)
• Hepatitis
• Thrombocytopenia
• Congenital varicella syndrome if maternal infection occurs in early pregnancy
• Neonatal varicella with severe outcomes if acquired around birth
• Later reactivation as shingles (herpes zoster)

References

• NICE Clinical Knowledge Summary: Chickenpox (2023)
• Public Health England Green Book: Chapter 34 – Varicella
• Royal College of Paediatrics and Child Health: Chickenpox in children guidance
• Royal College of Obstetricians and Gynaecologists (RCOG): Chickenpox in Pregnancy
• NHS UK: Chickenpox overview and care
• British National Formulary (BNF): Aciclovir and VZIG guidance