Smallpox: Symptoms

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Symptoms

The incubation period for smallpox is about 12 days. However, symptoms can develop as soon as 7 days or as long as 19 days after exposure.

During the first 2 to 3 days of illness, smallpox causes symptoms that affect the whole body (systemic symptoms), including:

• High fever, often rising to more than , then dropping over 2 to 3 days.
• Extreme lack of energy (lethargy).
• Severe headache.
• Severe backache.
• Severe abdominal pain and vomiting (in some cases).
• Delirium (in some cases).
• Seizures in some children.

Rash development and progression

After 2 to 3 days of severe illness, the smallpox rash appears in the mouth and throat, but it may not be noticeable. About 24 hours later, a rash appears on the face and arms. During the first week of rash, a large amount of the smallpox (variola) virus is in the saliva, making the infected person's saliva highly contagious. Spreading the virus through coughing and sneezing is most likely at this time.

Smallpox lesions appear on the skin over a 1- to 2-day period. Unlike a chickenpox rash, all smallpox lesions on the same part of the body change appearance at the same time, about every 1 to 2 days. Over a 2- to 3-week period, the rash progresses through the following stages:²

• Macules. Tiny flat, red spots usually appear first in the throat and mouth. However, these may go unnoticed until spots also show up on the face or arms. The rash then spreads to the rest of the body, becoming most concentrated on the face, feet, and hands.
• Papules. The red spots become bumpy, growing to about in diameter.
• Vesicles. The lesions fill with fluid, growing to about in diameter.
• Pustules. About 4 to 7 days after the rash appears, the lesions become firm, dome-shaped, whitish, and pus-filled, growing slightly larger with depressed centers. This stage lasts from 5 to 8 days.
• Crusts. By the second week of rash, the pustules crust over and turn into scabs. Scabs fall off 3 to 4 weeks after the rash first appears, leaving pitted scars.

Although a severe chickenpox infection may be mistaken for smallpox, there are numerous differences between chickenpox and smallpox . For example, the smallpox rash usually first appears in the throat and mouth or on the arms, and then moves to the torso. The chickenpox rash usually first appears on the torso, and pustules in many different stages are present at the same time (while some are new, others are crusting over).

Death

Up to 30% of people infected with smallpox die.⁴ The infection can overwhelm the body's defenses, leading to organ failure. However, all cases of smallpox took place before modern medical advances. So it is possible that less people would die if a smallpox outbreak were to occur today.

Last updated:	January 31, 2007
Author:	Debby Golonka, MPH
Reviewed By:	William M. Green, MD - Emergency Medicine, Christine Hahn, MD - Epidemiology
Editors:	Susan Van Houten, RN, BSN, MBA, Pat Truman, MATC