translation.en: Smallpox was a systemic disease, officially eradicated since 1979, caused by infection with the Variola major virus, whose only reservoir was infected humans.
translation.es: La viruela era una enfermedad sistémica (está erradicada oficialmente desde 1979), provocada por una infección por el virus Variola major, cuyo único reservorio eran los seres humanos infectados.