Secondary syphilis rash and inflammation on a back. Syphilis is caused by the Treponema pallidum bacterium. It is transmitted through sexual intercourse with an infected person. About 3-4 weeks after infection, a sore (chancre) appears at the infection site, healing within 2 months. About 6-12 weeks after infection, secondary syphilis occurs. The main symptom is a skin rash, with headache, fatigue and fever. Tertiary syphilis follows within 10 years of infection, with the formation of tumour-like gummas, causing neurological disorders. Treatment is with antibiotic drugs.