VD vs herpes

VD

noun
  • The design diving speed of an aircraft; the highest speed which the aircraft is planned to reach during flight testing. Always higher than VNE (the speed that must not be exceeded in service). 

herpes

noun
  • A viral infection, caused by Human alphaherpesvirus 1 and Human alphaherpesvirus 2, marked by painful, watery blisters in the skin or mucous membranes or on the genitals. 

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