What Causes Open Sores On Testicles,arms And Legs?

My brother recently started getting open soars on his testicles, arms, and legs. He had never had this happen to him till he had sex with his girlfriend a few days ago, she told me that she has a few open soars above her vagina about a inch below her underware line but I figure that rules out herpes because it spread to his arms and legs to? Do you have any clue what could have caused this