Chickenpox is caused by infection with the varicella zoster virus, a member of the herpes family of viruses.
The virus is spread in droplets of saliva through the air or by direct contact with the fluid from the blisters of the infected person. Coughing and sneezing are the most common modes of transmission, particularly in children.
One bout of chickenpox gives lifelong immunity from contracting the disease again. However, the virus remains in the body for life and can be reactivated years later as shingles (herpes zoster). Shingles can occur at any age but is most common in adults over 60 years of age.
Signs and symptoms
Twelve to 48 hours later the rash develops into small red spots. These then turn into yellow fluid-filled blisters, which burst and dry up 3-4 days after they appear. There may be several crops of spots occurring over 4-5 days. The spots cause itching, which may be severe. They may occur all over the body, including the mouth and genital area. Some people may have only a few spots whereas others will have hundreds.
Symptoms start appearing 10-21 days after exposure to the virus. Full recovery from chickenpox usually takes 7-10 days after the symptoms first appear.
Consult a doctor immediately if the person seems very sick, confused or difficult to waken, or if they have trouble walking or have a stiff neck. Also consult a doctor if the blisters become infected or if there are spots in the eyes, ears or mouth.
Chickenpox in otherwise healthy children does not normally require medical treatment - the infection is usually allowed to run its course.
High-risk individuals, including people with weakened immune systems and pregnant women who are not already immune to the varicella virus, may be given antiviral drugs such as acyclovir or varicella-zoster immunoglobulin (ZIG), which is a human blood product, to reduce the severity of chickenpox and risk of complications. However, to be beneficial, antiviral drugs and ZIG must be given very soon after exposure to the varicella virus.
People with chickenpox should remain at home until they are no longer infectious. Supportive treatment includes:
- Pain relief such as paracetamol to relieve fever. Aspirin should not be given, as this has been associated with Reye’s disease (a rare disorder affecting the liver and brain) in children with chickenpox
- Itching can be treated with lotions such as calamine available from a pharmacy.
- Tepid baths with sodium bicarbonate, uncooked oatmeal or colloidal oatmeal, or solutions such as Pinetarsol added can also be helpful in relieving itching
- Because the mouth and throat can be affected, offer soft food and cool drinks. Avoid salty foods and citrus fruits
- To prevent infection of the sores, trim children’s fingernails short or put gloves on their hands, and wash hands frequently with antibacterial soap. Discourage scratching as much as possible
- Dress children in light, loose fitting clothing or pyjamas. Overheating and friction from clothing can worsen itching
- Antihistamines such as diphenhydramine to help relieve itching.
Bacterial infection of the skin, which may need to be treated with an antibiotic, is the most common complication of chickenpox. Serious complications include pneumonia, septicaemia (blood infection), and rarely encephalitis (swelling of the brain) and death.
Chickenpox can cause foetal abnormalities and low infant birth weight if a non-immune woman contracts the disease between weeks 8 and 20 of pregnancy. Additionally, there is a risk of serious disease in the new-born baby if the mother contracts chickenpox between the fifth day before delivery and the second day after the baby is born.
Children with chickenpox should therefore be kept away from pregnant women and new-born babies until they are no longer infectious. Pregnant women who have not had chickenpox should see their doctor for control measures if they are exposed to the disease.
People with weakened or compromised immune systems – for example those who are HIV positive, organ-transplant recipients, and children with leukaemia – are also susceptible to serious illness as a result of varicella virus infection.
The chickenpox (varicella) vaccine is the best way to prevent chickenpox.
One dose of the vaccine provides approximately 99% protection against severe chickenpox and 80% protection against chickenpox of any severity. Vaccination may prevent or reduce the severity of chickenpox if it is given within 3–5 days of exposure to someone with the disease.
The varicella vaccine is available from GPs. It is fully funded for infants at 15 months of age or children at 11 years of age not previously infected with or vaccinated against chickenpox, as part of the New Zealand Ministry of Health’s national immunisation schedule. The varicella vaccine is also recommended and funded for certain high-risk groups and is available at a cost to other patients.
Further information and support
Immunisation Advisory Centre (IMAC)
Freephone: 0800 IMMUNE (0800 466 863)
Freephone: 0800 933 922
Freephone: 0800 611 116
Mayo Clinic (2019). Chickenpox (Web Page). Rochester, NY: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/diseases-conditions/chickenpox/symptoms-causes/syc-20351282 [Accessed: 25/03/19]
Ministry of Health (2017). Varicella (chickenpox). Immunisation Handbook 2017 (2nd edition, March 2018). Wellington: New Zealand Ministry of Health. https://www.health.govt.nz/publication/immunisation-handbook-2017 [Accessed: 25/03/19]
DermNet NZ (2016). Chickenpox (varicella) [Web Page]. Hamilton: DermNet New Zealand Trust. https://www.dermnetnz.org/topics/chickenpox/ [Accessed: 25/03/19]