Chicken pox and shingles are caused by the Herpes Zoster virus. It is also called the varicella-zoster virus(varicella is the medical name for chickenpox).

Chickenpox is a mild disease affecting most children. It is most common in the winter and spring and nearly all cases occur in epidemics, once every three years or so. It is most common between the ages of two and eight. The person is infectious from about two days before the rash appears until approximately five days after.

It is spread by inhaling infected droplets of saliva and nasal secretions coughed out by an infected person. The virus is present in these droplets before any rash appears, which is why it can spread rapidly. The rash takes the form of blisters, which burst and then scab over. The fluid in the blister is full of viruses, so traditionally it was thought that the risk of passing on the infection was still there until the last blister had burst and scabbed. However, the Public Health Laboratory Service now recommend that children need only be excluded from school for just 5 days, as transmission has not been reported beyond day five of the rash.

After a chickenpox infection, the viruses remain dormant in the nervous system and are kept in check by the immune system. At any time later in life, but usually in adulthood, the viruses can be reactivated, causing shingles.

Paracetamol may be taken to reduce fever. In severe cases an antiviral drug (acyclovir) may be prescribed, early in the course of the condition. Calamine lotion may be used to soothe the itchiness of the rash.

Symptoms

Chickenpox starts with a slight fever and a feeling of being unwell, sometimes with flu-like symptoms, approximately two to three weeks after infection. A rash appears in crops, typically behind the ears, under the arms, on the trunk, arms and legs.
It takes the form of small, itchy, red spots that become fluid-filled blisters within a few hours. They then dry out to form scabs in a day or two. Crops continue to appear for up to six days.

Chickenpox is almost always a very mild illness in children. It is rare but much more severe in adults, with a higher risk of complications.

Chickenpox can be caught from a person with shingles. A person with chickenpox cannot give someone shingles.