Smallpox
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 40°C (104°F), 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 chicken pox 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 2.5 mm (0.1 in.) in diameter.
- Vesicles. The lesions fill with fluid, growing to about 5 mm (0.2 in.) 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 centres. 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 chicken pox infection may be mistaken for smallpox, there are numerous differences between chicken pox and smallpox
Death
Up to 30% of people infected with smallpox die.5 The infection can overwhelm the body's defences, 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.
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| Author: | Debby Golonka, MPH Carrie Henley | Last Updated: May 1, 2007 |
| Medical Review: | William M. Green, MD - Emergency Medicine Anne C. Poinier, MD - Internal Medicine W. David Colby IV, MSc, MD, FRCPC - Infectious Disease Christine Hahn, MD - Epidemiology | |
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