Certain disease syndromes of the 18th and 19th centuries, such as sibbens (Scotland), radesyge (Scandinavia), and skerljevo (Bosnia), were called syphiloids because—while resembling syphilis in some respects—they were nonvenereal and rural, propagated endemically, chiefly among children, under the unhygienic conditions of primitive life in huts and villages.
A review of the category "syphiloid" in the Surgeon General's Index Catalogue (first series, 1893) in the light of modern knowledge, shows how awkward the word was; for it was then assumed to comprise not only the forms of treponematosis listed above, but also "pseudosyphilis," button scurvy, condyloma, boubas, and framboesia. These did not exhaust the list, which went so far as to include such nontreponemal conditions as leprosy, scabies, and verruga! It is not surprising that as time passed the inexact word syphiloid was dropped; it did not appear at all in the second series of the Index Catalogue (1912). Although it
Hudson EH. Endemic Syphilis—Heir of the Syphiloids. Arch Intern Med. 1961;108(1):1-4. doi:10.1001/archinte.1961.03620070003001