Syphilis rash in an AIDS patient. Scaly and lumpy syphilide (syphilis rash) on the arms of an AIDS patient from Africa. This rash has relapsed (returned) 4 weeks after treatment with penicillin antibiotic. HIV, the virus that causes AIDS, is interfering with the treatment of any diseases the patient may have. This is because HIV weakens the patient's immune system that defends against such infections. AIDS patients generally require longer treatments for infections. Syphilis is a disease caused by the Treponema pallidum bacterium. It is transmitted by sexual activity. AIDS is acquired immune deficiency syndrome. HIV is the human immunodeficiency virus.