Syphilis and HIV
Genital sores (chancres) caused by syphilis make it easier to transmit and acquire an HIV infection through sexual contact. There is an estimated two- to fivefold increased risk of acquiring HIV infection when syphilis is present.
Ulcerative STDs that cause sores, ulcers, or breaks in the skin or mucous membranes, such as syphilis, disrupt barriers that provide protection against infections. The genital ulcers caused by syphilis can bleed easily, and when they come into contact with oral and rectal mucosa during sex, the infectiousness of (and susceptibility to) HIV (human immunodeficiency virus) can increase tremendously. Having other STDs is also an important predictor for becoming infected with HIV, because STDs are a marker for behaviors associated with transmission of the virus.
Having an HIV infection at the same time can change the symptoms and course of syphilis.