The first symptoms of smallpox after infection with the virus usually occur after 12 to 14 days (the usual duration of incubation period). During the incubation period (which can range from seven to 17 days) the person appears and feels healthy and cannot infect others.
After the incubation period, the person suddenly develops flu-like signs and symptoms which include:
Smallpox rash develops a few days later. The rash characteristically appears as flat, red spots (lesions)of which many become small blisters filled with clear fluid (vesicles) and later, with pus (pustules) in a day or two. The rashes appear initially on the face, hands and forearms, and then spread to the trunk. It is initially most noticeable on the palms of the hands and the soles of the feet. Lesions can involve the mucous membranes of your nose and mouth as well.
After the pustules develop, the pain can be excruciating. After eight to nine days, scab begins to form, which falls off and leaves deep pitted scars. Unlike chickenpox in which rashes occur in crops, in smallpox all the lesions present in a specific area progress at the same rate through the different stages.
If a person does not recover, death usually occurs during the second week of illness.
Smallpox vs. Chickenpox: In the past, smallpox was often confused with chickenpox which is another viral illness with rashes. However, there are many important differences between chickenpox and smallpox:
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