Cause
The varicella-zoster virus, one of the herpes viruses, causes
chickenpox infection. The same virus that causes
chickenpox also causes
shingles. For more information on shingles (herpes
zoster), see the topic
Shingles.
How it is spread
The chickenpox virus can spread easily from one person to
another. It most often spreads through the respiratory tract, such as mucous
membranes of the mouth and nose. You also can get chickenpox through the air,
from an infected person's sneezing or coughing. Less often, chickenpox is
spread when fluid from a chickenpox blister gets on your skin. Chickenpox is
most contagious from 2 to 3 days before the rash develops until all the
blisters have crusted over.
On rare occasions, a person can get chickenpox from the fluid of
shingles blisters.