Frei's test links, nowadays, many different pathological processes nosologically classified as the Sixth Venereal Disease. It has been advanced that the infection by poradenic virus should be considered a general disease with three periods, like syphilis, and with anatomical changes more or less limited to the rectogenital area, although extra-genital localizations have been described.
The study of patients suspected of poradenic virus infection is sometimes difficult because the Frei's antigen is not always at hand; the buboes may be scarce and the activity of the antigen is limited. To overcome these difficulties, antigenic animal sources have been suggested, created by artificial infection of laboratory animals, and such sources now exist in the market ape and white mouse. In my routine work the ape antigen has proved to be not so reliable as the human antigen. Efforts have been made by others to prepare an antigen from the intestinal mucous membrane or from the human blood serum of patients.