SMALLPDX or VARIOLA, an acute infectious disease characterized by fever and eruption, which, after passing through various stages of papule, vesicle and pustule, dries up, leaving more or less distinct scars.
By far the most common cause of conveyance of the disease is contact with the persons or the immediate surroundings of those already affected. The direct cause is unknown. The disease is probably communicable from its earliest manifestations, but it is generally held that the most infectious period extends from the appearance of the eruption till the drying up of the pustules. No age is exempt from susceptibility. One attack of smallpox as a rule confers immunity, but there are numerous exceptions to this rule. Overcrowding and all insanitary surroundings favour the spread of smallpox where it has broken out ; but the most influential condition is the amount of protection afforded to a community by previous attacks and by vaccination (q.v.). Such protection, although for a time most effectual, tends to become exhausted unless renewed. Hence in a large population there is always likely to be an increasing number of individuals who have become susceptible to smallpox. This probably explains its occasional and even apparently periodic epidemic outbreaks in large centres, and the well-known fact that the most severe cases occur at the beginning—those least protected being neces sarily more liable to be first and most seriously attacked.
eruption begins to appear. It is almost always first seen on the face, particularly about the forehead and roots of the hair, in the form of dusky red erythematous spots which in the course of a few hours develop into true papules more or less thickly set to gether. The eruption spreads over the face, trunk and extremities in the course of a few hours—continuing, however, to come out more abundantly for one or two days. It is always most marked on the exposed parts. On the second or third day after the ap pearance of the papules they change into vesicles filled with clear fluid and show a slight central depression, giving the char acteristic umbilicated appearance. The clear contents of these vesicles gradually become turbid, and by the eighth or ninth day they are changed into pustules. The fully developed pocks in crease in size and lose the central depression.
Accompanying this change there are often marked inflammation and swelling of the skin, which render the features unrecognizable. The eruption is also present but in a modified form on the mucous membranes, that of the mouth and throat being affected early, and the swelling produced here is a source of danger, from ob struction in the upper air-passages. The mucous membrane of the nostrils may be similarly affected. The eyes may also be in volved, to the danger of permanent impairment of sight. The fever which ushered in the disease quickly returns to normal on the first appearance of the eruption but when the vesicles become converted into pustules, there is a return of the fever (secondary or suppurative fever), sometimes accompanied by great restless ness, delirium or coma. On the eleventh or twelfth day the pustules begin to dry up and the febrile symptoms decline. Great itching of the skin attends this stage. The scabs produced by the dried pustules gradually fall off and reddish brown spots remain, which leave permanent white depressed scars—this "pitting" so charac teristic of smallpox being specially marked on the face. Con valescence in this form of the disease is as a rule uninterrupted. In the majority of the cases developing in the United States during recent years no secondary fever has been seen.