Prior to its eradication, smallpox would need to be differentiated from other diseases that cause a vesicular rash and a fever including chickenpox (which was often mistaken for smallpox), herpes zoster and erythema multiforme.
Smallpox differential diagnosis
Chickenpox differential diagnosis
Roseola differential diagnosis
Smallpox risk factors
Chickenpox risk factors
Ebola differential diagnosis
Onychomycosis risk factors
Impetigo differential diagnosis