If anti-Semitism is a variety of racism, it is a most peculiar variety, with many unique characteristics. In my view as a historian, it is so peculiar that it deserves to be placed in a quite different category. I would call it an intellectual disease, a disease of the mind, extremely infectious and massively destructive.
We have grown accustomed to the wonders of clean water, indoor plumbing, laser surgery, genetic engineering, artificial joints, replacement body parts, and the much longer lives that accompany them. Yet we should remember that the vast majority of humans ever born died before the age of 10 from an infectious disease.
When I came to University of California, San Francisco to work on infectious disease, I looked around to different options, and malaria was particularly interesting and fascinating to me. It's amazing that after 100 years of study of this little parasite, we've not been able to effectively control it.
Like many physical diseases, anti-Semitism is highly infectious, and can become endemic in certain localities and societies. Though a disease of the mind, it is by no means confined to weak, feeble, or commonplace intellects; as history sadly records, its carriers have included men and women of otherwise powerful and subtle thoughts.