A 30-year-old male, Kallu, with a history of sexual exposure comes with a painless indurated ulcer over the penis with eveed margins. The diagnosis is

Syphilis is a sexually transmitted disease caused by Treponema pallidum. Infectivity of a patient to the sexual paner is maximum during first two years of the disease. It multiplies at the site of entry. Clinical features sets in after an incubation period of about a month. The primary lesions in syphilis are the chancre at the site of entry of spirochete which is genital. The chancre is painless, relatively avascular, circumscribed indurated, superficially ulcerated lesions. Ref: Ananthanarayan and Paniker&;s Textbook of Microbiology, 9th edition; Pg no 372