Primary syphilis. A chancre (sore) on a penis due to infection with syphilis. The sore is a red pai- nless ulcer on the foreskin. Chancres are small ulcers teeming with bacteria. Syphilis is caused by infection with Treponema pallidum a spirochaete bacterium, spread through sexual intercourse with an infected person. About 3-4 weeks after infecti- on, the sore appears at the infection site, it heals within 4-8 weeks. About 6-12 weeks after infection secondary syphilis occurs. The main sym- ptom is a skin rash. Tertiary syphilis follows within 10 years of infection. Tumour-like gummas form causing neurological & cardiovascular disord- ers.Treatment involves penicillin antibiotic drugs.