Can you please tell me how scarlet fever and strep throat differ?

A Rash. Scarlet fever is strept throat with a rash. Otherwise it is exactly the same symptoms, possible complications and therapy.
Definition is strep. The term "scarlet fever " applies to strains of strep a that have the additional dna to make a red rash. The infection may be in the throat, or other site (skin, anus) and still produce the rash and fever. Strep throat includes strains of strep a that may or may not produce a rash.Their location in the throat is rather specific.