An elderly man comes to the clinic seeking help for something that has been bothering him for a little more than a week. The man complains of skin

An elderly man comes to the clinic seeking help for something that has been bothering him for a little more than a week. The man complains of skin irritation and a rash on his leg that appears to be spreading. He says he started "feeling bad" a week ago, but only noticed the "rash" 3 days ago. The pain and irritation has gotten bad enough that he hasn't even been able to take care of his prize-winning rose bushes. During your examination you find that he has a slight fever and elevated blood pressure. His leg shows a series of ulcers beginning near his knee and ending near his genitals. There is evidence that he has been scratching his leg and that the ulcers weep.

What does he have? Explain your answer.