Author: Vanessa Ngan, Staff Writer, 2002. Updated by Dr Jannet Gomez, October 2016.

What is chickenpox?

Chickenpox is a highly contagious viral infection that causes an acute fever and blistered rash, mainly in children.

The name may be derived from the French term for chick pea, chiche pois. Another theory is that the word 'chicken' was derived from a slang term for 'child'. Chickenpox is also known as varicella.

Who is at risk of chickenpox? 

Chickenpox occurs worldwide, affecting persons of all races, gender and age. However, most cases occurring in children before they are 10 years of age.

Once a person has had the chickenpox infection, it is unlikely he or she will get it again, as it confers lifelong immunity.

Immunocompromised individuals are susceptible to the virus at all times and should take measures to prevent or modify the course of the disease if there has been exposure to the virus. 

What is the cause of chickenpox?

Chickenpox is caused by primary infection with the varicella-zoster virus, of the herpesviridae family. This virus is sometimes called herpes virus type 3.

How do you get chickenpox?

Chickenpox is highly contagious and is easily spread from person to person by breathing in airborne respiratory droplets from an infected person's coughing or sneezing or through direct contact with the fluid from the open sores.

A person who is not immune to the virus has a 70–80% chance of being infected with the virus if exposed in the early stages of the disease.

What are the signs and symptoms of chickenpox?

In children, chickenpox usually begins as itchy red papules progressing to vesicles on the stomach, back and face, and then spreading to other parts of the body. Blisters can also arise inside the mouth

The spread pattern can vary from child to child. There may be only a scattering of vesicles, or the entire body may be covered with up to 500 vesicles. The vesicles tend to be very itchy and uncomfortable.

Some children may also experience additional symptoms such as high fever, headache, cold-like symptoms, vomiting and diarrhoea. 

Chickenpox is usually more severe in adults and can be life-threatening in complicated cases. Most adults who get chickenpox experience prodromal symptoms for up to 48 hours before breaking out in the rash. These include fever, malaise, headache, loss of appetite and abdominal pain. Chickenpox is usually more severe in adults and can be life-threatening in complicated cases.

The blisters clear up within one to three weeks but may leave a few scars . These are most often depressed (anetoderma) but they may be thickened (hypertrophic scars). Scarring is prominent when the lesions get infected with bacteria.


See more images of varicella ...

How is chickenpox diagnosed?

Diagnosis of chickenpox is usually made on the presence of its characteristic rash and the presence of different stages of lesions simultaneously. A clue to the diagnosis is in knowing that the patient has been exposed to an infected contact within the 10–21 day incubation period. Patients may also have prodromal signs and symptoms.

Laboratory tests are often undertaken to confirm the diagnosis.

  • PCR detects varicella virus in skin lesions and is the most accurate method for diagnosis.
  • Culture of blister fluid is time consuming and is less frequently performed.
  • Serology (IgM and IgG) is most useful in pregnant women, or prior to prescribing immune suppression medication to determine need for pre-treatment immunisation.

What is the treatment for chickenpox?

For most healthy patients with chickenpox symptomatic therapy is usually all that is required.

  • Trim children's fingernails to minimise scratching.
  • Take a warm bath and apply moisturising cream.
  • Paracetamol can reduce fever and pain (do not use aspirin in children as this is associated with Reye syndrome).
  • Calamine lotion and/or oral antihistamines may relieve itching.
  • Consider oral aciclovir (antiviral agent) in people older than 12 years, which reduces the number of days with fever.

Immunocompromised patients with chickenpox need intravenous treatment with the antiviral aciclovir. In cases of inadvertent exposure to the virus, varicella-zoster immune globulin if given within 96 hours of initial contact can reduce the severity of the disease though not prevent it.

What are the complications from chickenpox?

In healthy children, chickenpox infection is usually an uncomplicated, self-limiting disease. Complications may include:

  • Secondary bacterial infection of skin lesions caused from scratching
    • Infection may lead to abscess, cellulitis, necrotising fasciitis and gangrene
  • Dehydration from vomiting and diarrhoea
  • Exacerbation of asthma
  • Viral pneumonia

Some complications are more commonly seen in immunocompromised and adult patients with chickenpox.

  • Disseminated primary varicella infection; this carries high morbidity
  • Central nervous system complications such as Reye syndrome, Guillain-Barré syndrome and encephalitis
  • Thrombocytopenia and purpura 

Varicella in pregnancy

  • Exposure to varicella virus in pregnancy may cause viral pneumonia, premature labour and delivery and rarely maternal death.
  • Approximately 25% of fetuses become infected. Offspring may remain asymptomatic, or develop herpes zoster at a young age without previous history of primary chickenpox infection.

Shingles (herpes zoster) 

  • The varicella zoster virus remains dormant in sensory ganglia after infection.
  • It may reactivate after many years as shingles. Shingles presents with grouped vesicular lesions usually affecting a single dermatome.
  • Other infections occurring as a result of reactivation of virus include  post-herpetic neuralgia, vasculopathy, myelopathy, retinal necrosis, cerebellitis and zoster sine herpete.

How to prevent the spread of chickenpox

A person with chickenpox is contagious 1–2 days before the rash appears and until all the blisters have formed scabs. This may take between 5-10 days. Children should stay away from school or childcare facilities throughout this contagious period. Adults with chickenpox who work amongst children, should also remain home.

It can take from 10–21 days after contact with an infected person for someone to develop chickenpox. This is how long it takes for the virus to replicate and come out in the characteristic rash in the new host.

As chickenpox may cause complications in immunocompromised individuals and pregnant women, these people should avoid visiting friends or family when there is a known case of chickenpox. In cases of inadvertent contact, see your doctor who may prescribe special preventive treatment.

Vaccination against chickenpox

Vaccination is available for chickenpox, and is highly recommended.

Chickenpox is highly preventable by vaccination with live attenuated varicella vaccine. The vaccine is subsidised ("scheduled") for non-immune individuals that are immunosuppressed or are in other special groups. It will be added to the scheduled and funded immunisation programme for infants aged 15 months in New Zealand in July 2017.  Refer to the Immunisation Advisory Centre for further up-to-date information.


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