Chickenpox

What is chickenpox?

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

The name may be derived from the French term for chickpea, chiche pois. Another theory is that the word 'chicken' was derived from a slang term for 'child'.

Skin rash of chickenpox

Chickenpox on back 

Chickenpox 

Chickenpox 

Who is at risk of chickenpox?

Chickenpox occurs worldwide, affecting persons of all races, sex and age. Most cases occur in children before they are ten 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 herpesvirus type 3.

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 to someone in the early stages of the disease.

What are the clinical features 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.

Cutaneous features of chickenpox

Chickenpox on face 

Chickenpox 

Chickenpox 

Oral mucosal lesions of chickenpox

Chickenpox 

Chickenpox 

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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. See also chickenpox pathology.

Laboratory tests are often undertaken to confirm the diagnosis.

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

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 by scratching
  • Infection may lead to abscess, cellulitis, necrotising fasciitis and gangrene
• Dehydration from vomiting and diarrhoea
• Exacerbation of asthma
• Viral pneumonia
• Chickenpox lesions may heal with scarring.

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

• Non-immune pregnant women should take care to avoid contact with people who have chickenpox and to wash hands frequently when handling food, animals, and children. Exposure to varicella virus in pregnancy may cause viral pneumonia, premature labour and delivery and rarely maternal death.
• Approximately 25% of fetuses of mothers with chickenpox become infected. It is harmless to most of them. Offspring may remain asymptomatic, or develop herpes zoster at a young age without a previous history of primary chickenpox infection. They may also develop congenital varicella syndrome, one of the TORCH infections.
• Congenital varicella syndrome occurs in up to 2% of fetuses exposed to varicella in the first 20 weeks of gestation. It can result in spontaneous abortion, fetal chorioretinitis, cataracts, limb atrophy, cerebral cortical atrophy and microcephaly, cutaneous scars, and neurological disability.
• Mortality in newborns infected with varicella is up to 30%.

Perinatal varicella

• If a mother develops chickenpox just before delivery or during the 28 days after delivery, her baby is at risk of severe 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, which usually affect 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.

Complications of chickenpox

Scars from chickenpox 

Herpes zoster 

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
  • Avoid NSAID use outside of hospital settings due to the increased risk of severe cutaneous complications such as invasive group A streptococcal superinfections.
  • Do not use aspirin in children as this is associated with Reye syndrome.
• Calamine lotion and oral antihistamines may relieve itching.
• Consider oral aciclovir (antiviral agent) in people older than 12 years, which reduces the number of days with a 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. This is used where there is no previous history of chickenpox (or the patient has no antibodies to the varicella-zoster virus on blood testing) in pregnancy, in the first 28 days after delivery, and in immune deficient or immune-suppressed patients.

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 5–10 days. Children should stay away from school or childcare facilities throughout this contagious period. Adults with chickenpox who work among children should also remain home.

It can take 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 infants aged 15 months in New Zealand as well as non-immune individuals who are immunosuppressed or are in other special groups. If in New Zealand, refer to the Immunisation Advisory Centre for up-to-date information.