Chickenpox 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 takes 11-20 days to develop symptoms after being in contact with the virus (the 'incubation period').
It is spread by direct contact with broken chickenpox blisters or by inhaling infected airborne droplets.
The rash takes the form of blisters, which burst and then scab over. Traditionally it was thought that the risk of passing on the infection was still there until the last blister had burst and scabbed. However, it is 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.
If a woman is exposed to chickenpox or shingles when pregnant, there is no problem if she has already had chickenpox as a child as she is immune. 85% of women have antibodies to the chickenpox virus and therefore their baby is not at risk of chickenpox even if the mother develops shingles during pregnancy.
If the woman has not had chickenpox or is unsure if she has, she should see her doctor to arrange a test for antibodies as soon as possible. If this shows she has not had chickenpox and has no antibodies, then chickenpox antibodies can be given to stop the disease developing. This is best given within 4 days (but is probably of use within 10 days) of coming into contact with the virus.