Chickenpox, also known as varicella, is a highly infectious disease caused by the varicella-zoster virus and is most commonly seen in children.
Very few people avoid chickenpox in countries where the disease is common. This is because more than 8 out of 10 people susceptible to chickenpox will become infected after exposure to the virus. It is very rare for a person to get chickenpox more than once.
After recovery from chickenpox, the virus stays dormant (inactive) in the nerves near the spine. Years later the virus can become active again and cause herpes zoster, commonly known as shingles. Shingles usually affects adults 50 years of age or older and people of any age with a weakened immune system (see herpes zoster).
The virus can spread from person to person through droplets in the air from coughing, sneezing or laughing. It can also be transferred by direct contact with the fluid that is in the chickenpox or shingles rash blisters.
A person with chickenpox can pass the virus on for 1-2 days before they get the rash until after the rash blisters have dried up, which usually takes 5-7 days.
The early symptoms of chickenpox may include a mild fever, loss of appetite, headache and feeling tired, followed by the appearance of a red rash that becomes blistered and itchy, mostly on the trunk, head and face with some on the arms and legs. The blisters can occur in the eyes, mouth and throat, vagina and urinary tract. For up to 5-7 days, new blisters appear, filled with liquid containing the virus which then form crusts that fall off after 1-2 weeks.
Chickenpox is usually mild in children, with most healthy children recovering fully. However for some it can be more severe requiring hospitalisation, and in rare cases, death. Complications can include skin infections, inflammation of the brain, pneumonia and blood infections. Chickenpox tends to be more severe in adolescents and adults, pregnant women and their unborn babies and people of any age with poorly functioning immune systems.
Those who catch the disease from another household member often have more severe chickenpox than the person they caught it from.
For healthy children the main treatment measures include reducing pain, discomfort and itching associated with the blisters, preventing dehydration and skin infection, and as necessary providing early antibiotics if skin infection does occur.
For healthy adolescents and adults, the use of antiviral medicine, such as acyclovir, should be considered in addition to comfort measures. Antiviral medicine started within 24 hours of the rash appearing may reduce the severity of the disease. (See ‘After exposure’ below.
Tips for managing chickenpox symptoms:
Aspirin or any medicine with an ingredient name including the words ‘salicylate’ or ‘salicylic acid’ MUST NOT be given to children with chickenpox because of the risk of Reye’s Syndrome.
Changes in skin colour after the blister crusts fall off may last for months. Permanent scarring may also occur.
Around one in every 20 healthy children with chickenpox will develop a bacterial skin infection, usually from scratching, that needs to be treated with antibiotics. If untreated, bacterial skin infections can lead to bacterial infection in other parts of the body, including the blood (septicaemia). This can be serious and lead to death.
Although rare, chickenpox infection can cause inflammation in other parts of the body, such as the central nervous system, joints (arthritis), bones, lungs (pneumonia), liver (hepatitis), blood vessels supplying the brain with blood and brain.
Pneumonia is more likely to occur as a complication in adults, particularly women in the last trimester of pregnancy.
Maternal chickenpox during pregnancy can infect the fetus. The highest risk period is during the first 20 weeks of pregnancy. Up to two in 100 infants exposed to chickenpox before birth will be born with congenital varicella syndrome and may have skin scarring, eye, limb and brain abnormalities, developmental delay and a poor outcome. Maternal chickenpox, within five days before and two days after delivery, can infect the newborn infant. Up to 30 in 100 newborns with chickenpox develop severe disease that can result in death.
Prior to exposure
Chickenpox vaccine is delivered to children on the immunisation schedule at 15 months of age. Vaccination is recommended for non-immune adolescents and adults, and non-immune woman prior to pregnancy. People with a weakened immune system are at high risk, but may not be able to have the vaccination themselves, so close contacts of these people are recommended to be vaccinated. The vaccine is funded for certain high-risk individuals and/ or their close contacts.
*Pregnant women with no reliable history of chickenpox should have an urgent blood test to check for immunity after exposure to chickenpox. If the blood test suggests no immunity against chickenpox, they can receive ZIG within 96 hours of exposure, or wait for the onset of symptoms and begin antiviral medicine immediately.