Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
After infection, symptoms may take from seven to 17 days to appear for major types of smallpox. The virus begins growing in the bloodstream 72-96 hours after infection, but no obvious symptoms appear immediately (see multimedia files below for clinical presentations of smallpox infections).
People who have contracted smallpox initially develop such symptoms as fever, body aches, headache, chills, and, particularly, backache. Over half of people with smallpox experience chills and vomiting. About 15% become confused.
A rash appears 48-72 hours after the initial symptoms and turns into virus-filled sores, which later scab over. The process can take up to
Just after the rash appears, the virus is highly contagious as it moves into the mucous membranes. The body sheds the cells, and virus particles are released, coughed, or sneezed into the environment. The infected person can be infectious for up to
three weeks (until the scabs fall off the rash). Live virus can be present in the scabs. After the scabs or crusts fall off (in
two to four weeks), a depression or light-skinned scar remains.
Early in the course of the disease, the rash and pus-filled sores can easily be mistaken for chickenpox. Lesions occur first in the mouth and spread to the face, then to the forearms and hands, and finally to the lower limbs and trunk. In contrast, rash from chickenpox progresses from the arms and legs to the trunk and rarely forms in the armpits, palms, soles, and elbow areas.