Definition: A chronic infectious disease caused by the syphilis spirochete, when the spirochete enters the body, it rapidly spreads to all organs of the body, producing various symptoms and signs, and can also be latent, and can also be transmitted to the next generation through the placenta, so it is extremely dangerous. Etiology: The pathogen is syphilis spirochete, discovered by Schaudinn and Hoffmann in 1905, about 8-10mm long, with 6-12 spirals, because it is transparent and not easy to stain, with refractive power, can not be detected under the ordinary microscope, so also known as pale spirochete, an anaerobic parasitic bacteria, in the human body Can survive and reproduce for a long time, but not easily survive in vitro, boiling, drying general disinfectants (soap, carbolic acid, alcohol, etc.) will easily kill it, in 41-42 ℃ for 1 to 3 hours can also be killed, but in low temperature (-78 ℃) can survive for several years. At present, syphilis spirochetes can not be cultured, but can be inoculated in the testes of exempted children in order to preserve and pass on the strain for laboratory use. Transmission: Most of the infection is transmitted through direct contact with sexual intercourse, syphilis spirochetes are infected through broken skin or mucous membrane, and a few are infected through kissing, breastfeeding, blood transfusion, towels, etc. Pregnant women with syphilis can transmit it to the fetus through the placenta. Syphilis immunity: It is generally believed that syphilis does not have innate immunity, and acquired immunity is also very weak, so it can not prevent the second reinfection, syphilis patients can produce antibodies to syphilis spirochetes in the serum, but so far, it is not possible to implement passive immunity, syphilis, if completely cured, if reinfection can still develop, humans have cellular and liquid immune response to syphilis spirochetes, in terms of humoral immunity, the spirochetes into the body, the spirochetes can produce many antibodies. In terms of humoral immunity, the spirochete enters the human body and produces many antibodies, the earliest being IgM, followed by IgG and IgA, all of which can be detected except for the earliest stage, and even exist for life. In terms of cellular immunity, patients with stage I and II syphilis lack a delayed hypersensitivity response to spirochete antigens, and such a response does not appear until after stage II.