Syphilis is a complex sexually transmitted disease caused by a bacterium called Treponema pallidum . It is transmitted by contact with infected sores or lesions, from mother to baby or through blood contact. Soon after the organism enters the body it spreads throughout the body via the bloodstream or the lymphatic system. Nearly all organs can be invaded, including the central nervous system. If left untreated, syphilis can persist for decades and eventually be fatal.

At various times, it has been suggested that syphilis is the cause of AIDS, is a co-factor with HIV for AIDS, or causes HIV-associated dementia. None of these ideas has stood up to rigorous scientific investigation. However, as for many sexually transmitted infections, it is extremely likely that syphilis increases the risk of HIV transmission.

In some parts of the world, syphilis remains a common heterosexually transmitted disease. The World Health Organization (WHO) estimated in 1999 that of a global total of 12 million adults with syphilis, eleven million were living in sub-Saharan Africa, Latin America and south and south-east Asia.

In recent years there has been a striking increase in the number of cases of syphilis in Eastern Europe, especially in the former Soviet Union. In Western Europe and North America, while there are some cases reflecting international contacts, there has also been an increase in cases amongst gay men which seem to reflect changing patterns of sexual behaviour and pose a particular risk of increased HIV transmission.1 Notably, oral sex has been identified as the route of transmission in Chicago in 14% of cases of syphilis, particularly in gay men.2 However, the increase in syphilis diagnoses in gay men has not yet been followed by an increase in new HIV infections in the United States or the United Kingdom, as originally feared.3 4

In the United Kingdom, syphilis has re-emerged as a relatively common sexually transmitted disease. Between April and December 2001, the Communicable Disease Surveillance Centre received 207 reports of infectious syphilis from genitourinary medicine clinics in London. The overwhelming majority of cases (73%) were among gay or bisexual men, with the remaining 56 cases occurring among heterosexuals, including 20 women. Fifty-four percent of the gay men with syphilis were known to be HIV-positive, compared with only 2% of heterosexuals with syphilis.

In 2003, there were 1575 cases of syphilis diagnosed in the United Kingdom, mainly clustered in London and Manchester. Most of the cases were in gay men, many of whom are HIV-positive. This represents a 23% increase on 2002, but may be explained in part by more people coming forward for testing. Figures for 2004 continued to show the same trend, with an increase of 37% on the previous year. In comparison with previous years, women and heterosexual men represented an increasingly large proportion of these cases, with rises of 47 and 45% over 2003, respectively.


  1. Hopkins S et al. HIV acquisition during an outbreak of syphilis in Dublin. Ninth Conference on Retroviruses and Opportunistic Infections, Seattle, abstract 771-W, 2002
  2. Centers for Disease Control and Prevention (CDC) Transmission of primary and secondary syphilis by oral sex--Chicago, Illinois, 1998-2002. MMWR Morb Mortal Wkly Rep 53: 966-968, 2004
  3. Dilley JW et al. Trends in primary and secondary syphilis and HIV infections in men who have sex with men in San Francisco and Los Angeles, California, 1999-2002. MMWR Morb Mortal Wkly Rep 53: 575-578, 2004
  4. Murphy G et al. HIV incidence appears constant in men who have sex with men despite widespread use of effective antiretroviral therapy. AIDS 18: 265-272, 2004