“Vicious dog” means either of the following:
(a) Any dog that, when unprovoked, in an aggressive manner, inflicts severe injury on or kills a human being.
(b) Any dog previously determined to be and currently listed as a potentially dangerous dog that, after its owner or keeper has been notified of this determination, continues the behavior described in Section 31602 or is maintained in violation of Section 31641, 31642, or 31643.