The Reference Desk/What is the Crimson Horror?

Gatiss is a little vague on this one. At time he indicates the Crimson Horror is the red leech. At other times it's the venom. And at still others, it's the disease imparted by the venom. At present, crimson horror redirects to red leech, and the Crimson Horror redirects to the episode page. That's almost certainly not gonna cut it. How should we best handle these various meanings?