Chickenpox is a common, highly infectious, usually self-limiting viral illness caused by the varicella zoster virus. Varicella is a type of herpes virus – and like other herpes viruses – after the virus has been contracted it may remain dormant in the host for many years – and can sometimes reactivate. In the case of varicella – reactivation of the virus causes the illness shingles.
Although chickenpox is usually mild, it can cause pneumonia (more properly a pneumonitis) and in those who are immunocompromised and in neonates it can cause a serious disseminated (widespread to many organs) illness.
It is possible to be infected (including developing immunity) and never develop the clinical syndrome of chickenpox.
The virus is typically airborne and enters the body through the respiratory tract. Viraemia (virus in the blood) can be detected 4-6 days later, but the first symptoms don’t usually occur until 10-14 days after exposure and it can be as long as 21 days. There may be a short prodromal period of a few days before the rash develops. The rash is quite characteristic and can usually be diagnosed clinically.
Usually, no specific treatment is required and most cases resolved within about a week of the onset of the rash. A patient is considered no longer infectious once all of the lesions of the rash have crusted over.
Neonates and those who are immunocompromised, as well we pregnant women who are not immune may receive specific treatment such as IV immunoglobulin or the antiviral medication aciclovir.
In recent years, vaccines against varicella have been developed. In Australia it is now routine to vaccinate children against chickenpox – this comes in combination with the MMR vaccine – the MMRV vaccine – and is given with he third dose of the MMR at age 18 months. A single dose of varicella vaccine is required. Shingles is a significant cause of morbidity in older populations and vaccination is hoped will reduce the incidence of shingles in future, as well as the incidence of chickenpox and the risks of chickenpox in pregnancy.
Epidemiology and Aetiology
Varicella can be passed on by either an active case of chickenpox or an active case of shingles – however chickenpox is much more infectious than singles. Varicella is endemic in most countries and tends to occur in outbreaks. The peak time of year is in spring.
- Over 90% of the population have contracted the illness by the age of 15 in endemic areas (this stat is from the UK)
- Less common in tropical and subtropical regions
- Infection tends to occur before the age of 10 in most developed countries. An older age is more common in warmer climates
- Patients are infectious from a few days before the lesions show, until all the lesions have crusted over. Some sources suggest this is from day 8-21 after exposure
- Is it not possible to “catch shingles. Shingles is a reactivation of the varicella virus in a host who has previously had chickenpox. However it is possible to catch chickenpox from someone who has shingles – however this is rare. Covering up the lesions of shingles reduces the risk.
The rash of chickenpox has a specific pattern and the diagnosis can usually be made clinically on the basis of this rash.
- The rash occurs in “crops”
- Each crop consists of a handful of spots
- The first crop is typically on the head, neck or torso
- Further crops follow several hours (up to 12 hours) later
- Over the course of 24-72 hours the rash becomes widespread on most of the body – the limbs are usually less severely affected
- The lesions at first are discreet red raised lesions
- These becomes fluid fills blisters, before crusting over and drying out
- There are usually patches in different places not he body going through a different part of this process
- The patient is considered to no longer be infectious once all the lesions have crusted and dried
- Marks are often visible for several weeks, but only rarely does it cause long term scarring
- The rash may be itchy bit isn’t always
- Females may have painful vulval lesions
- secondary bacterial infection of the lesions can occur – this is also more common in eczema
Other symptoms include:
- Fever – may be for up to 4 days
- Headache, myalgias – these can start several days before the rash begins
- In those two have been previously immunised a very mild form of the disease may develop
- Pneumonia is a rare but serious complication
- Diagnosis is almost always clinical
- Swabs of the fluid from blister can be sent for laboratory confirmation but this is not usually necessary
Most cases in previously well individuals do not require specific management. Children aged >1 week and <12 years do generally not require any specific treatment. The illness can be more severe in teenagers and adults. Advice should be given about:
- Avoiding scratching
- Antihistamines and emollients (moisturises) are effective to reduce the itch
- Calamine lotion is NOT recommended as the effect ceases as soon as it dried (which is usually very quickly)
- Avoid pregnant women, neonates and those who may be immunocompromised until all the lesions have dried and crusted over
- Patients should isolate from school / work until no longer infectious
- Encourage adequate fluid intake
- Paracetamol may be given for fever and headache
- 15mg/Kg QID in children
- 1g QID in adults
- Avoid the use of ibuprofen and other NSAIDS
- These can increase the risk of group A strep (GAS) infection when given with varicella virus
- Aspirin should be avoided in children due to increase risk of Reye syndrome
- Aciclovir should be considered in those who are immunocompromised, pregnant or have serious illness. You may also consider prescribing it in those who present in the first 24 hours as it may reduce disease severity
- Not recommended in children unless systemically unwell or immunocompromised. Specialist advise should be sought
- Patients whom are considered at higher risk include:
Contacts who are at high risk of disease (See risk factors above) should be considered for prophylactic management
- VZIG can be given cup to 10 days after exposure as long as no rash has developed. More effective the earlier it is given
- Those who are known to not be immune can be vaccinated after exposure but before symptoms develop
- Early treatment with aciclovir may also be considered
- Secondary skin infection
- Occurs in up to 20% of cases
- More likely in patients who scratch a lot!
- Secondary bacterial infections – particularly groups A streptococcus (GAS)
- This is a serious illness that can cause necrotising fasciitis and toxic shock syndrome
- Viral pneumonia
- Can be fatal (very rare)
- More common in older children and adults
- Symptoms usually start within 4 days of onset of the rash
Varicella in pregnancy
Contracting varicella for the first time in pregnancy can cause serious and life-changing consequences. Varicella if contracted in the first 20 weeks of pregnancy can cause fetal varicella syndrome (FVS) – which can result in birth defects – of the skin, eyes, brain and gastrointestinal tract.
- This occurs in <1% of cases
Later in pregnancy there is a higher risk of stillbirth. Mothers than contact varicella in the last 4 weeks before birth can also pass on the virus to the child which can lead to the potentially life-threatening neonatal varicella. Varicella in pregnancy may also cause a serious illness in the mother – and can cause complications such as pneumonia.
- Primary varicella infection affects 3 in 1000 pregnancies in the UK
- Women from tropical and subtropical areas are at greater risk due to the reduced immunity in these areas
In Australia – all. mothers are screened for varicella immunity at the start of pregnancy. In the UK this is not routine but may be offered if there is no known previous history of infection or vaccination. If it is found that the mother is not immune:
- She should be advised about the risks of varicella in pregnancy and to avoid contact with anyone known to have chickenpox or shingles
- She should be advised to inform a healthcare worker immediately if she is known to be exposed to varicella
- She should be offered vaccination in the post-natal period (after the birth). Vaccination is not usually recommended during pregnancy. It is safe to breast-feed after vaccination
RCOG guidelines suggest the following for managing exposure and infection during pregnancy:
- Women with a known high risk exposure should be offered intravenous immunoglobulin (IV VZIG). This is effective for up to 10 days after exposure.
- Note that if you receive VZIG then you are potentially infectious for longer than if you don’t (form 8-28 days after exposure as opposed to 8-21 days in people who don’t receive it
- A second dose may be required if there is another exposure and more than 3 weeks has passed since the first dose was given
- Women who develop a rash need to be isolated form other pregnant women – this can have implications for their antenatal care
- Oral aciclovir can be given to women who develop a chickenpox rash
- Before 20 weeks this is associated with teratogenic effects (but risk is probably lower than chickenpox risks)
- After 20 weeks generally considered safe and should be offered to all women after this gestation
- Course is usually 1 week long
- IV aciclovir should be given to all women with serious symptoms
- VZIG is of no benefit once the rash has developed and should not be given
- Chickenpox (varicella) – RCH
- Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
- Chickenpox in pregnancy – RCOG
- NSW Health – Immunisation schedule – accessed on 25/06/2023
- NHS vaccines and when to have them
- Chickenpox vaccine – NHS