The varicella-zoster virus causes chickenpox. In rare cases, a person infected with the virus may develop a slightly different form of chickenpox. These variations include the following.

Varicella bullosa

Varicella bullosa is a type of chickenpox mainly seen in children younger than 2. The rash is made up of large blisters instead of small blisters. However, the course of the illness is the same as chickenpox.

Congenital varicella syndrome

When a woman has chickenpox during pregnancy, she passes the virus to her fetus. The fetus then gets chickenpox. This is called congenital varicella syndrome.

Complications from chickenpox in a fetus are very rare. However, if a fetus has chickenpox in the first 3 months of development, he or she may be born with certain birth defects such as one limb (usually a leg) smaller than the other, scars on the limbs, or eye problems such as cloudy lenses. The baby can also weigh less than expected at birth, develop seizures, or have mental retardation.

Fetuses who get chickenpox from their mothers will not have chickenpox again. However, they can still have shingles. They may even have shingles as babies or young children.