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Variola virus causes smallpox, the disease which is now extinct.
The incubation period varied from 10 to 14 days. The prodro-mal phase, which correlated with the phase of viremia, was the first to appear. Onset of disease was sudden. The condition manifested as sudden onset of fever, severe headache, nausea, pharyngitis, body malaise, and backache. An exanthematous rash would appear on the palate, tongue, and pharynx during the later part of the prodromal stage.
The smallpox rash was characterized by skin lesions that are in the same stage of evolution, unlike those lesions seen in chickenpox. The lesions in chickenpox appear in successive waves and in various stages, such as vesicles, pustules, and scabs.
The skin lesions first appear on the face and extremities and then spread centrifugally to the trunk. These lesions begin as macules and then develop into papules, vesicles, pustules, and finally crusts during a period of approximately 17 days. The lesions heal with formation of characteristic scarring.
Overwhelming toxemia was the usual cause of death in patients with smallpox. There were two variants of small-pox: variola major and variola minor. The variola major was associated with a fatality rate of 25–30%, while variola minor was associated with a low fatality rate of less than 1%. In addition, flat smallpox and hemorrhagic variola were the unusual mani-festations of smallpox in some patients, and were usually fatal.
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