Impassioned
Passionate Enthusiasm, Passionate, Vehement
noun, な adjective
This fever is violent. This is the feeling you get when you have crazy passionate enthusiasm, aka you are impassioned.
ねつれつ
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
彼女はどうやらお前の熱烈なファンみたいだな。
She seems to be a passionate fan of yours.