sandfly fever vs disease

sandfly fever and disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
sandfly fever	Yes	No	No	No
disease	Yes	No	No	No

As nouns, disease is a hypernym of sandfly fever; that is, disease is a word with a broader meaning than sandfly fever:

sandfly fever: a mild viral disease transmitted by the bite of the sand fly Phlebotomus papatasii
disease: an impairment of health or a condition of abnormal functioning

sandfly fever (noun)	disease (noun)
a mild viral disease transmitted by the bite of the sand fly Phlebotomus papatasii	an impairment of health or a condition of abnormal functioning