Syphilis, if untreated, is a serious chronic bacterial infection caused by the spirochete Treponema pallidum; it is usually transmitted by direct sexual contact. Initially a painless skin blemish appears, followed about six weeks later by a generalized rash, low-grade fever and malaise that may last a few months. Symptoms then disappear during a latent period that can last years. The final and most serious stage of the disease (more or less 10 years after infection) is characterized by: ulceration of skin, palate and bones, with scarring and disfigurement; involvement of the main blood vessel (aorta), leading to angina pectoris and serious or fatal heart disease; involvement of the nervous system, with resulting epileptic fits, insanity, blindness, deafness, unsteadiness in walking, crippling joint involvement, bladder disturbance, ulcers on the soles, and palsies.
The disease also increases the likelihood of transmission of HIV. Syphilis during pregnancy may result in miscarriage, stillbirth, or an infant with congenital syphilis, who may develop deafness and blindness as well as mental retardation and other debilitating complications.
In poor communities, syphilis can be a non-venereal disease, transmitted by overcrowding and by the use of common eating and drinking vessels (nonvenereal treponematoses include Endemic syphilis, Yaws, Pinta, and Bejel and Njovera syphilis). As social conditions improve and the chances of non-venereal contact diminish, syphilis evolves into a venereal disease, although the persistence of unhygienic practices or deteriorating social conditions may result in mixed venereal and non-venereal syphilis. A community's syphilis rate is a key indicator of the quality of its public health service.
In the West, syphilis is now fairly uncommon and could be eradicated, with the number of new cases in the USA falling to its lowest level in 40 years in 1997. The US rate is 10 times the Canadian rate of 0.4 cases per 100,000 people. The rate in US blacks is 30 times the rate in US whites and is on the rise among Hispanics.
High prevalence rates for early syphilis occur wherever there is social disruption and mass population movements, as in some parts of Southeast Asia and Africa. In developed countries, there has been a rise in the incidence of infectious syphilis. Congenital syphilis is still a serious disease resulting in foetal wastage, neonatal mortality and infant morbidity in countries where the services dealing with sexually transmitted diseases and with maternal and child health are poorly developed. A disconcertingly high prevalence of venereal syphilis has been observed as a consequence of the eradication of yaws in countries where syphilis control has not been carried out simultaneously.
Homosexual transmission is an epidemiological factor of increasing importance. In the USA the proportion of men with infectious syphilis who named other men as sexual partners has recently increased by almost 200% in cases of primary and secondary syphilis infections in males, and in Australia in 1973 homosexuals accounted for 73.2% of the total male cases. In the UK, the proportion of early syphilis cases which had been acquired as a result of homosexual activity increased from 42.4% in 1971 to 54% in 1977. This association between homosexuality and syphilis transmission appears to be more pronounced in developed countries, although some reports from developing countries - for example Sri Lanka and India - also make reference to the importance of homosexual transmission. The high infection and reinfection rates among homosexuals make this relatively small group an important reservoir of infection which may contribute significantly to the transmission of syphilis in the community at large. Syphilis and other sexually transmitted infections that cause genital ulcers facilitate the spread of HIV-virus through homosexual and heterosexual contact.