Chickenpox is an infection with a blistering rash, which is caused by the Varicella virus. This virus also causes shingles.
The incubation period - the length of time from exposure to the virus to developing the condition - is 2 to 3 weeks. If someone in the house has chickenpox, the likelihood of someone else in the house catching it, who has not already had it, is as much as 90%.
The spots appear over a few days and progress from being red spots to forming blisters which eventually burst, dry and crust, ultimately to heal. The spots are very itchy and if the child scratches and infects them they will leave scars.
By the time the spots have stopped forming and are dried over and the temperature has fallen back to normal, the child is no longer infectious. This usually takes a week and until then they should remain off playgroup or school.
Chickenpox does not normally make children very ill, and for most, the main problem is the itchiness. Your doctor will not normally need to see the child, but you should let him know that the child has had it. Chickenpox may be severe in adults and people with a severe case of chickenpox may be given an antiviral drug.
You are infectious for 2 days before the rash appears and for 5 days after. Once you have had chickenpox you are immune and rarely catch it again, however the virus can re-activate to cause shingles. People with chickenpox should stay away from others who have not had chickenpox until their rashes have dried up.
Many people find that calamine lotion helps soothe the itch and paracetamol helps ease aches and pains and also keeps down the temperature.
Pregnant women should contact their GP immediately if they are in contact with a person with the disease.