1911 Encyclopædia Britannica/Chicken-pox

CHICKEN-POX (Syn. varicella, a Low Latin diminutive of variola), a specific contagious disease characterized by an eruption of vesicles in the skin. The disease usually occurs in epidemics, and is one of childhood, the patients being generally between two and six years old. The incubation period is from ten to fifteen days; there are practically no prodromal symptoms, the only indication being a slight amount of fever for some twenty-four hours, after which the eruption makes its appearance. A number of raised red papules appear on the trunk, either on the back or chest; in from twelve to twenty-four hours these develop into tense vesicles filled with a clear fluid, which in another thirty-six hours or so becomes opalescent. During the fourth day these vesicles dry and 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 the chest, but it also occurs on the face and limbs, and on the mucous membrane of the mouth and palate. The temperature begins to fall after the appearance of the rash, but a certain slight amount may persist after the disappearance of all symptoms. It rarely rises above 102° F. The disease runs a very favourable course in the majority of cases, and after effects are rare. One attack does not confer immunity, and in numerous cases one individual has had three attacks. The diet should be light, and the patient should be prevented from scratching the spots, which would lead to ulceration and scarring. After the first few days there is no necessity to confine the patient to bed. In the large majority of cases, it is easy to distinguish the disease from smallpox, but in certain patients it is very difficult. The chief points in the differential diagnosis are as follows. (1) In chicken-pox the rash is distributed chiefly on the trunk, and less on the limbs. (2) Some of the vesicles are oval, whereas in smallpox they are always hemispherical. They are also more superficial, and have not at the outset the hard shotty feeling of the more virulent disease. (3) The vesicles attain their full growth within twelve to twenty-four hours. (4) The pustules are usually monocular. (5) There is no prodromal period.