Symbolism, Imagery, Allegory
Like it or not, syphilis does indeed function as a symbol in Candide. You might have noticed lots of references to original sin. Right? Well, syphilis was doing a little European tour at the time Voltaire was writing Candide, and so, according to some scholars, Voltaire seems to be making a little religious analogy here: Syphilis, like original sin, spreads through sex.