WHO/AFRICAN SERIES / WHO-Spx-Dx-Africa39-MedRes
The disease most frequently confused with smallpox is chickenpox. In most patients the diseases are quite different, but in a few patients the diagnosis can only be made by laboratory tests. In chickenpox the fever usually begins at the same time as the rash or only a few hours before; in smallpox the patient is usually sick for 2 to 4 days before the rash appears. The smallpox rash, as we have seen, develops comparatively slowly through a series of stages, and at any one time all the pocks on a particular area of the body look very similar. In chickenpox new lesions continue to appear over a period of several days to a week and develop much more rapidly. Consequently, several stages of the rash can be seen at the same time on any part of the body.