I've just come out of a two-year-long obsession with mad cow. If you live in North America, and didn't eat beef in the UK or France between 1986-96, you don't have much to worry about at all. There are very strict regulations in place (particularly in my Canada) to control the spread of infection amongst cows and to make sure that, even if infection occurs, it won't make it to the human food supply. (And you can trust that it will remain that way because of how much everyone loves beef, and how little everyone wants to die of vCJD.)
Even if infected beef somehow made it to your plate from the few infected cows that have been in North America, the risk of transmission via oral consumption is probably small. We think this because of the small number of cases being reported compared the millions of people in the UK and elsewhere in Europe who likely consumed infected beef. I remember hearing about a hypothesis that many humans have a genetic resistance to the disease-causing prion protein because of our history of cannibalism. This was proposed when researchers observed that many individuals in the Fore tribe in Papua New Guinea appeared to have a resistance to the closely related disease "Kuru," which is caused by the same agent, and which was contracted when members of the tribe cannibalized recently deceased relatives before the practice was banned. If my basic understanding of evolutionary biology does not fail me, the idea is that if a human didn't have a resistance to the disease, he/she didn't survive to pass on his/her genes, and therefore the weak gene became less common.
When I was working through the fear with my therapist (who is also a GP) and asked if I had anything to worry about, he said "no" without hesitation. He said that even after I told him about my history of heavy beef consumption (especially the low-quality "beef" in things such as cheap hamburgers and beef patties). Obviously, that's rarely good enough for someone with severe OCD, and we still had a lot of work to do after that, but perhaps it will provide some perspective.
TL; DR: DON'T WORRY