scarlet fever vs scarlatina

scarlet fever and scarlatina both are nouns.

Word	Noun	Adjective	Verb	Adverb
scarlet fever	Yes	No	No	No
scarlatina	Yes	No	No	No

As nouns, scarlet fever and scarlatina are synonyms defined as:

scarlet fever and scarlatina: an acute communicable disease (usually in children) characterized by fever and a red rash

scarlet fever (noun)	scarlatina (noun)
an acute communicable disease (usually in children) characterized by fever and a red rash	an acute communicable disease (usually in children) characterized by fever and a red rash