internecine vs pestiferous

internecine

adj
  • Mutually destructive; most often applied to warfare. 

  • Characterized by struggle within a group, usually applied to an ethnic or familial relationship. 

pestiferous

adj
  • containing organisms that cause contagious diseases 

  • annoying, vexatious 

How often have the words internecine and pestiferous occurred in a corpus of books? (source: Google Ngram Viewer )