In variants where the spell of cure sickness can be cast directionally, casting it at Pestilence has some detrimental effect on him, probably hitting his HP and possibly stunning or even cancelling him.

In variants where you can cast cure sickness directionally as a beam, that beam damages monsters with a disease attack.

Merge extra healing, cure sickness and cure blindness, and make the resulting spell level 6. Or just merge cure sickness with cure blindness, and call it “cure ailment”.