Antisemitism was present before ww1, yes. Though i can not say how they were treated during ww1, after they were a subject of persecution in Britain in Londons East end which had the majority of eastern european Jews. The fascist oragnisation British Brothers League often had marches through this part of London, and even Churchill had some antisemitic quotes in common belief that prominent revolutionaries in Russia had been jewish.

Other examples are books like 'The Protocols of the Elders of Zion' which was the first explicit book example I can think of. I am a Modern history masters student so I am not completely sure, but I believe that there are examples of antisemitism since before the middle ages.