I find it a little ironic that the conceptualization of ideas as infectious diseases dates back far beyond The Selfish Gene. In fact, one of the first notable observations of this ideology is from the medieval Catholic Church, circa 12th century. Heresy was considered to be an infection of the mind which spread from person to person:
Heresy (from the Latin, secte) meant treason to God, the worst offense against Christian society. Heresy meant contamination — an infection from which true believers had to protect themselves.
It appears that the church knew full well that ideas worked like disease, and perhaps that their own docterine was in competition with the ideas of heretics. And this a full 700 years before the discovery of evolution. I find it mildly ironic that Dawkins would cite the Church as his prime example, but forget to cite their invention of the concept.