CHICKEN POX

also called Varicella, contagious viral disease characterized by an eruption of vesicles (blisters) in the skin. The disease usually occurs in epidemics, and the patients are generally between two and six years old, although they can be of any age. The incubation period is at least two weeks; there are practically no premonitory symptoms, though slight fever for about 24 hours may precede the eruption. A number of raised, itching red papules appear on the back or chest; in from 12 to 24 hours these develop into tense vesicles filled with a clear fluid, which in another 36 hours or so becomes opalescent. During the fourth day these vesicles shrivel up and the scabs fall off, leaving, as a rule, no scar. Fresh spots appear during the first three days, so that at the end of that time they can be seen in all stages of growth and decay. The eruption is most marked on areas covered by clothing, but it also occurs on the face and limbs and on the mucous membrane of the mouth and palate. The temperature rarely rises above 39 C (102 F). The disease runs a favourable course in most cases and usually produces permanent immunity. Negative aftereffects are rare. During initial treatment, the patient should be isolated and confined to bed. The diet should be light, and the patient should be prevented from scratching, which could lead to ulceration of the vesicles and scarring. Chicken pox is caused by the varicella-zoster virus, the same virus that causes herpes zoster (shingles). Chicken pox is the clinical reaction to a first exposure to the virus. After clinical recovery of the patient, the virus may settle in a nerve cell and be reactivated many years later. The cause of reactivation is not known. Upon reactivation, the virus travels along a nerve to the skin and causes shingles. A person with herpes zoster is able to infect another person with chicken pox, but the reverse seems not to occur, because herpes zoster generally appears after a period of latency. Occasionally, however, herpes zoster occurs in children as the primary response to the virus. Injections of zoster immune globulin (ZIG), a preparation made from the blood of adults who have recently had shingles, are sometimes given to prevent the development of chicken pox in exposed children. ZIG contains antibodies to the varicella-zoster virus and provides temporary protection against the virus. ZIG administration is usually reserved for children with leukemia or immune-system disorders, for whom varicella poses significant risks. A chicken-pox vaccine was developed in Japan in the early 1970s and has been used widely there. In 1995 a vaccine prepared from a live, weakened strain of the virus was approved for use in the United States. See also herpes zoster.