Hi! I completed a significant amount of research towards this topic and the answer is: there is no specific origin or root of anti-semitism. Rather, anti-semitism is the culmination of hate over time reinforced by specific events. Since the idea came about of Jewish Deicide (the Jewish people being accused of killing Jesus) the Jewish people became the most available minority to exercise scapegoating.
Scapegoating is blaming a person or group of people for your personal misfortunes.
Initially during the Feudal period of Europe, Jewish people were unable to obtain any jobs because the social system was created for Christian people (look up Pope Innocent III and Cannon Law). As a result, Jewish people were only able to take jobs that were considered "sinful", such as money lending. Additionally Jewish people often would be tax collectors for Kings, from which the stereotype of Jewish people being greedy for money etc. originated from.
Then one event happened which generally did change how Europeans viewed Jewish people was the Black Death. When the Black Death occurred people in Europe had no idea why everyone around them was suddenly dying of this disease. Now, since the idea of "Cannon Law" existed (as I mentioned earlier) Jewish communities were generally completely secluded from actual cities. Thus, Jewish people rarely interacted with Christian people unless they needed to do their job (for example, Jewish people did not use the same wells as Christians and Christians later accused the Jewish people of poisoning their wells). Additionally, Jewish people have a custom that prior to eating hands must be washed. As a result, Jewish communities were much less affected by the Black Death than Christian communities. And when Christians noticed that the Jewish people were less affected, the Christians targeted their fear and anger towards the Jewish communities spread around Europe. In Germany, Italy, France, and England communities of Jewish people were sacked and hundreds of Jewish people were murdered because people blamed them for "causing" the Black Death.
Since then, the Jewish people have been viewed as a "force of evil" who are "out to get" the Christians of this world. (I am simply stating fact). Martin Luther's anti-Semitic writings are a perfect example of how the view of Jewish people changed after the Black Death (as his writings became the building blocks for Hitler's hate speech).
So while there is no origin, the Black Death definitely influenced how Europeans viewed Jewish communities. I hope this answers your question.