vicious

He had always been remarkably immune from such little ailments, and had only once in his life been ill, of a vicious pneumonia long ago at school. He hadn't the faintest idea what to with a cold in the head, he just took quinine and continued to blow his nose.

, Folio Society, 2006, vol.1, p.195:

We may so seize on vertue, that if we embrace it with an over-greedy and violent desire, it may become vicious.