Chickenpox (varicella), which infects millions of children each year in the United States, is the disease most frequently confused with smallpox. There are key differences between the two diseases:
| Smallpox incubation |
7-17 days
|
Chickenpox incubation |
14-21 days
|
| Smallpox prodrome
(illness prior to rash)
|
2-4 days
|
Chickenpox prodrome
(illness prior to rash)
|
minimal/none
|
| Smallpox distribution |
1. Lesions initially tend to develop on the face and extremities, progressing to the trunk of the body.
2. Rash found on palms and soles.
|
Chickenpox distribution |
1. Lesions initially tend to develop on the trunk of the body, progressing to the face and extremities. Lesions also tend to be more abundant on trunk than on face and extremities.
2. Rash rarely found on palms and soles.
|
|
Smallpox depth of rash
|
Deeply embedded
|
Chickenpox depth of rash
|
Superficial |
| Smallpox progression of rash |
Lesions develop and progress at the same rate. |
Chickenpox progression of rash |
Lesions appear successively and progress at varying rates. |
| Smallpox scab formation |
10-14 days after rash onset |
Chickenpox scab formation |
4-7 days after rash onset |
| Smallpox scab separation |
14-28 days after rash onset |
Chickenpox scab separation |
<14 days after rash onset |
| Smallpox communicable period |
From rash onset until all scabs have separated (3-4 weeks after onset of rash). Most infectious during the first week of rash, after prodrome. |
Chickenpox communicable period |
As long as 5 days (but usually 1-2 days) before rash onset until all lesions are crusted (usually) about 5 days after rash onset). Most infectious 1-2 days before rash onset and for first few days of rash. |
For further information regarding smallpox:
contact Orange County Public Health/Epidemiology: (714) 834-8180
or go to:
JAMA consensus article: Smallpox as a Biological Weapon:
http://jama.ama-assn.org/cgi/reprint/281/22/2127.pdf
Information adapted from: Los Angeles County Department of Health Services, Acute Communicable Disease Control
