Syphilis is a chronic, systemic sexually transmitted disease caused by the pale (syphilis) spirochete. It is mainly transmitted through the sexual route and can be clinically manifested as stage I syphilis, stage II syphilis, stage III syphilis, latent syphilis and congenital syphilis (fetal syphilis). Syphilis is classified as a Class B disease in the Prevention and Control of Infectious Diseases Law of the People’s Republic of China. How is syphilis transmitted? Syphilis patients are the only source of infection. Syphilis spirochetes are found in large numbers on the surface of skin and mucous membrane damage, as well as in saliva, breast milk, semen and urine. Untreated patients are the most infectious within a year of infection, and become less and less infectious as the disease lengthens, and those with more than 4 years of disease are not infectious through sexual contact. It can also be invaded through dry skin and intact mucous membranes. A few can be transmitted through close contact such as kissing, breastfeeding, etc., but the syphilis spirochete must be attached to the contact site. Because syphilis spirochetes are anaerobic, they do not survive easily in vitro and are extremely sensitive to dryness, so the chance of indirect infection through various artifacts is extremely small. 2, blood transfusion infection If the blood donor is syphilis current patients transfusion can be transmitted to the recipient of blood. 3.Fetal transmission Pregnant women with syphilis are vertically transmitted to the fetus through the placental bloodstream. Generally in the first four months of pregnancy, due to the protective effect of the trophoblast, syphilis spirochetes can not pass, so the fetus is not infected in the first four months of pregnancy, later the trophoblast atrophy, syphilis spirochetes can enter the fetus through the placenta to infect the fetus.