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Varicella (chickenpox)

Varicella (chickenpox) is an acute, contagious disease caused by varicella zoster virus.  Individuals with chickenpox develop a rash of lesions that look like blisters over their body.  The lesions usually begin around the neck, scalp, face, trunk, and then to the extremities.  The highest concentration of lesions are found on the trunk (chest and back).  Lesions are usually 1-5 mm in size (size of a pencil eraser).  Once the rash appears, it progresses fairly rapidly over 1-2 days.  The number of lesions varies.  Some people get just a few lesions while others can be covered from head to toe.  The lesions develop vesicles which are delicate and contain clear fluid.  The vesicles may rupture or become cloudy before they dry up and crust over.  This process of “crusting over” usually takes about a week.  Children will in addition to developing a rash also have a general malaise (not feeling well), mild fever and itching.

Chickenpox is transmitted either indirectly by the respiratory tract (airborne) or by direct contact with the fluid from a lesion.  Children are most contagious 1-2 days prior to development of their rash.  Many times children spread the virus before they even realize they have it.  Children will continue to be contagious until the last of the lesions have crusted over.  This “crusting over” process usually takes from 7-10 days.  The incubation for chickenpox is from 10-21 days ( usually 14-16 days) from the time the child was exposed.

With the availability of the varicella vaccine since 1995, many children have been immunized against this virus.  This vaccine has resulted in a greatly decreased number of chickenpox cases seen in school.  While most children (99%) have immunity once they receive the vaccine, there is a 1% occurrence of what is referred to as “breakthrough infection”.  If a child does develop chickenpox after they had been immunized, their breakthrough infection is much milder than unvaccinated children.  It has been my experience that the lesions tend to be smaller in size and number.  These Children experiencing a “breakthrough infection” are also considered contagious until the last lesion has crusted over.  This process of crusting over takes about a week.