If the causal agent concerned in the production of syphilis is still unknown, it is not from any lack of attempts to discover it. At a recent meeting of one of the German medical societies, Lassar of Berlin stated his belief that in the past twenty-five years twenty-five parasites of syphilis had been discovered. Those who remember Aesop’s fable of “The Boy Who Cried Wolf” will readily appreciate the attitude of the general run of the medical profession toward anyone who comes forward with a new cause of syphilis. One is reminded, too, of the remark of the sage therapeutist, that the chance that we possessed a specific remedy for a given disease was in inverse ratio to the number of drugs which were claimed to be efficacious in its treatment. There is little doubt, however, reasoning from analogy, that syphilis is an infectious disease due to a parasite, the only point at issue being the exact nature of its cause. On account of the recent discoveries of protozoon-like bodies in certain of the exanthemata, several observers have hazarded a guess that syphilis is a protozoan infection, though one can not help suspecting that it might just as well be due to some ultramicroscopic parasite.
The Etiology of Syphilis. JAMA. 2014;312(18):1935. doi:10.1001/jama.2013.279832