Typically, symptoms of Smallpox will appear 1-2 weeks after the initial exposure. During the first stage of the disease, called the incubation period, the individual will look and feel normal and is not contagious. The incubation period is when the disease is multiplying inside the body. Initial symptoms of Smallpox are often difficult to diagnose due to their similarity to flu symptoms. The first symptoms of Smallpox may include a high fever, chills, severe muscle aches, vomiting, and head and backaches.
After the incubation period, the individual will then move into what is called the prodome phase, where the individual becomes more contagious, and the flu-like symptoms will increase in their severity and make it difficult to carry out day-to-day tasks. During this phase, the individual will start to develop the beginnings of the Smallpox rash. The rash starts out as red spots that are not raised. After a few days, the spots will turn into raised lesions filled with a clear fluid which are called vesicles. A few days later, the spots that were filled with clear fluid will then fill with pus, and turn into pustules. The spots will have a very distinct shape, which is much like a normal pustule but will have a small depression in the middle.
When the rash develops, the individual will continue to have a very high fever. One of the most hallmark symptoms of Smallpox is the way in which the rash is distributed throughout the body. The rash will almost always first appear on the face and inside the mouth, and then move down the trunk of the body, spreading to the arms and the legs. After the rash moves over the entire body, the lesions will be most noticeable on the palms of the hand and soles of the feet. The most painful stage of Smallpox is when the pustules burst. The pustules will not break the skin, like normal pustules do, but the layer of skin will actually separate from the base layer, which can be excruciatingly painful. After this stage, scabs will eventually form over the burst pustules. Those who don't recover from Smallpox will usually die during the second week after the onset of the disease.