crab louse vs venereal disease

crab louse

noun
  • A parasitic insect, Pthirus pubis, that lives amongst the pubic hairs of humans and feeds on blood. 

venereal disease

noun
  • Any of several contagious diseases, such as syphilis and gonorrhea, contracted through sexual intercourse. 

How often have the words crab louse and venereal disease occurred in a corpus of books? (source: Google Ngram Viewer )