chancroid vs crab louse

chancroid

noun
  • A sore characteristic of this infection. 

  • A sexually transmitted infection, caused by bacteria of species Haemophilus ducreyi, characterized by painful sores on the genitalia. 

crab louse

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

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