A man presents to a dermatologist because of a severe mucocutaneous rash that involves most of his body,including his palms and soles. Questioning reveals that he is a merchant marine who several months previously had an encounter with a prostitute in Southeast Asia. Which of the following is the most likely causative agent of this rash?

The rash described is that of secondary syphilis, caused by Treponema pallidum. Involvement of palms and soles by a rash is unusual, and secondary syphilis should come to mind. Not all patients with secondary syphilis have a severe form of the rash, and consequently some cases are missed. Primary syphilis takes the form of a painless, button-like mass called chancres. Teiary syphilis, which is now rare, has a propensity for involving the aoa and central nervous system and can also cause "gummas" (granulomatous-like lesions) in many sites, notably including liver and bone. Herpes simplex I usually causes perioral Herpes simplex II usually causes genital vesicular lesions. HIV does not itself cause a rash, although coinfection with other organisms can result in a rash. Ref: Ray C.G., Ryan K.J. (2010). Chapter 37. Spirochetes. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.