Overview
Also known as human herpesvirus 3, varicella-zoster virus (VZV) is a DNA virus that can cause chickenpox (varicella) and shingles (herpes zoster). Chickenpox is a primary infection by VZV, and shingles is its reactivation.
People with chickenpox should avoid close contact with at-risk groups, including pregnant people and immunocompromised states (discussed below).
Pathophysiology
VZV is highly contagious and spread by the respiratory route. In the skin, its replication can cause epithelial damage, resulting in vesicles containing damaged material and leukocytes. These may burst and spread VZV or resolve. After infection, VZV can remain latent in the dorsal root ganglia. Childhood exposure to chickenpox leads to lifelong immunoglobulin G (IgG) antibodies which persist for life, however, over time, the immune system is less effective at suppressing VZV, resulting in its reactivation and shingles.
Transmission
Chickenpox is:
- Highly infectious and around 90% of susceptible close contacts develop it
- Spread by respiratory droplets or direct contact with skin lesions
- Infectious from 24 hours before the rash appears until the vesicles are dry and have crusted over (usually 5 days)
It has an incubation period of 1-3 weeks and it is possible for chickenpox reinfection, but uncommon.
Epidemiology
- Chickenpox is predominantly a childhood illness
- More than 90% of people >15 years old are immune
Presentation
The typical features of chickenpox include:
- A febrile prodrome – may cause nausea, myalgia, anorexia, headaches, malaise
- Followed by an itchy rash:
- First, small, erythematous macules appear on the head and trunk before spreading
- They then become papules, vesicles, and itchy pustules
- Crusting usually occurs within 5 days of the rash onset and crusts fall off after 1-2 weeks
Investigations
Overview
Laboratory tests are rarely required in primary care unless exposure to chickenpox has occurred in at-risk groups.
Management
Chickenpox Exposure In High-Risk Groups
Overview
Although chickenpox is generally mild in children, people who are immunocompromised and/or pregnant are at a higher risk of complications, including disseminated disease and foetal complications. In some cases, post-exposure prophylaxis is offered.
Any person who is pregnant or immunocompromised should seek advice if they develop symptoms of chickenpox or have had exposure, regardless of whether they have had antiviral or immunoglobulin treatment, a history of chickenpox/shingles, or a VZV vaccine.
Management of exposure in pregnancy
Post-exposure prophylaxis depends on the immunity of the person to chickenpox. In a person with a definite chickenpox/shingles history or two doses of VZV vaccine who is not immunocompromised, no action is needed.
If there is any uncertainty or no history of shingles/chickenpox, check VZV IgG urgently:
- ≤20 weeks + not immune: give VZV immunoglobulin (VZIG) immediately
- This is effective up to 10 days-post exposure
- >20 weeks + not immune: give VZIG or antivirals (e.g. aciclovir) at days 7-14
Exposure in immunocompromised states
Seek same-day specialist advice in people who are immunocompromised and have no VZV IgG. They are often offered VZIG.
Management
Chickenpox in children
- 1st-line: supportive treatment – paracetamol, topical calamine lotion
- School exclusion – children should be kept away from school or nursery until all vesicles have crusted over (around 5 days after the onset of the rash)
- Safety-net: they should return if they deteriorate or if features of complications occur including bacterial superinfection or dehydration
- Avoid contact with pregnant and immunocompromised people
Chickenpox in pregnancy
Seek same-day specialist advice if chickenpox develops during pregnancy:
- ≥20 weeks + presents within 24 hours: give oral aciclovir
- <20 weeks: consider aciclovir
Complications
In children
Bacterial superinfection – a secondary bacterial infection superimposed on chickenpox:
- Most commonly caused by Group A Streptococcus (Streptococcus pyogenes) and Staphylococcus aureus
- Presents with sudden high-grade fever (often after initial improvement), erythema, and tenderness around the original chickenpox lesions
- May lead to impetigo, cellulitis, erysipelas, necrotising fasciitis, and scarring
- The use of NSAIDs may increase this risk
Rare complications include:
- Pneumonia
- Neurological complication – Reye’s syndrome (if aspirin is used, which is contraindicated in children), encephalitis, meningoencephalitis, cerebellar ataxia
- Disseminated haemorrhagic chickenpox
- Glomerulonephritis
- Henoch–Schönlein purpura
- Pancreatitis
- Keratitis
In adults
Increased severity – adults with chickenpox are more likely to be admitted to hospital and around 80% of mortality is due in adults. The risk is increased with advancing age.
Primary viral pneumonia – is the most common complication in adults. The risk and severity is higher in people who smoke.
Shingles – due to the reactivation of latent VZV.
In pregnancy
Maternal complications
Severe chickenpox – the risk and severity of complications including pneumonia, hepatitis, and encephalitis is higher. Around 1/10 with chickenpox develop pneumonia.
Foetal complications
Foetal varicella syndrome (FVS) – VZV infection in the first 28 weeks of pregnancy can lead to FVS, which can cause skin scarring, ophthalmic problems (e.g. microphthalmia), limb hypoplasia, and neurological abnormalities (e.g. microcephaly, learning difficulties, and bowel/bladder dysfunction).
In neonates
Disseminated/haemorrhagic varicella – can be fatal. Around 50% of neonates are infected if the mother is infected during the 4 weeks post-delivery.
Shingles of infancy/early childhood – a maternal infection >20 weeks can cause shingles in the newborn. This is thought to be due to the reactivation of VZV after a primary in utero infection.
In immunocompromised people
Disseminated/haemorrhagic varicella – the risk is higher in people who are immunocompromised (e.g. corticosteroid use, immunosuppressive drugs such as methotrexate, HIV etc.)
Increased risk of complications – including pneumonia, encephalitis, hepatitis, and disseminated intravascular coagulopathy.
Prognosis
- In most cases, chickenpox is self-limiting and relatively mild
- Recovery from a primary chickenpox infection usually leads to lifelong immunity, however, chickenpox recurrence in health people has been reported, but uncommon
- This is more likely to occur in people who are immunocompromised
