The enhanced growth rate of whistler-mode waves has been evaluated during an extended interchange event in the Io torus that occurred between 1709--1715 UT, on December 7, 1995. The energetic electron population observed by the Galileo EPD instrument is modeled using a bi-loss-cone distribution function (composed of a highly anisotropic component and a quasi-isotropic component). During the injection event, the path integrated gain increases by more than a factor of ten over a broad frequency range near a few tenths of the electron gyrofrequency, consistent with the observed enhancement in Galileo PWS emissions. The enhanced PWS emissions are mainly associated with an increase in the flux of cyclotron resonant electrons below 55 keV. Scattering of electrons by the enhanced whistler-modes causes the pitch-angle distribution of resonant electrons to evolve from a normal pancake distribution in the unperturbed torus to a quasi-isotropic distribution during the interchange event. This change provides an enhanced flux of electrons with mirror points close to Jupiter, which could be important for understanding the enhancement of Jovian auroral emissions in association with electron injection events.