Chicken Pox (Varicella)Organism
Chickenpox is caused by a virus varicella zoster and is a common childhood infection in the West. Although generally a mild illness, it can be severe and even fatal on occasion, particularly in adults and the immuno-suppressed. After initial infection with varicella zoster virus, the virus is not completely cleared from the body but persists lifelong in a latent state, and can reactivate intermittently causing shingles. Chickenpox can be very severe in pregnant women, and can cause foetal abnormalities in the early stages.
Mode of Transmission
Chickenpox is one of the most contagious infectious diseases, being transmitted by direct contact with the patient or articles soiled with fluid leaking from skin blisters, as well as being air borne and transmitted by inhalation of infected droplets coughed by another individual.
Regions AffectedVaricella zoster virus is common throughout the western world, and is found world-wide. It is less common in Asia and the Far East, where a smaller percentage of individuals become infected in childhood. This poses a significant risk to individuals from these areas if they travel to live in Europe since they are likely to contract severe chickenpox in adulthood.
PreventionThe risk of developing chickenpox can be reduced by isolating patients with chickenpox and taking care with articles soiled by their secretions (although there is a strong argument for exposing healthy young children to patients with chickenpox to prevent more severe infection in later life). If an individual is exposed, the risk of developing this disease can be reduced by taking preventative anti-viral drugs, or by the administration of antibodies to the varicella zoster virus; this latter approach is used frequently in non-immune pregnant women exposed to chickenpox. There is a vaccine available, as discussed below.
ImmunisationA live attenuated vaccine for chickenpox has recently been licensed in the UK, but has been used for much longer periods in the United States. This is effective in inducing immunity in most individuals and is generally well tolerated, causing a mild rash in a small proportion of healthy children. If the vaccine is used to protect children with impaired immunity against subsequent chickenpox, there is a higher chance of vaccine associated rash.
The vaccine should not be given to individuals with severe immune deficiency because it is a live vaccine. In the United Kingdom, the vaccine is used mainly for healthcare workers who have never previously been infected with varicella zoster virus, but its use is likely to be extended in the future.
Chickenpox antibodies are available for particular patients who have been exposed to chickenpox but not yet developed illness. Non-immune pregnant women should be given this to reduce the risk of chickenpox in pregnancy, with the possibility of congenital abnormalities in the infant. It may also be used in patients with impaired immunity due to illness or immuno-suppressive drugs.
Symptoms and Signs
After an incubation period of around 2 weeks (10 to 21 days), patients develop fever, headache and muscle aches, and after a couple of days a blistering rash that typically starts on the head and upper chest and spreads down the body, with relative sparing of the limbs.
Blisters are oval shaped and filled with clear fluid or pus. Painful blisters or ulcers may also appear in the mouth or genital area, and in fact can occur throughout the gut, causing abdominal pain.
Patients remain unwell for several days; gradually the blisters dry up, crust and heal without scarring (unless scratched).
Last Editorial Review: 25/1/2010