Reddit mentions of Anti-Judaism: The Western Tradition

>most primordial form of antisemitism

Actually, antisemitism as a thing itself predates both Christianity and Islam by a fair amount. Nirenberg's book Anti-Judaism: The Western Tradition (here) writes that the earliest known antisemitic text is from the beginning of the third century BCE, by an Egyptian named Mantheo. Check out this JCPA article about it as well.