The Lancet, a UK medical journal, in a rather grisly story, is reporting that Bovine Spongiform Encephalopathy (BSE), commonly known as "Mad Cow Disease", may have started in humans. It is claimed that feed imported to the UK from South Asia in the 1960s and 70s may have included the remains of human corpses. These corpses could have been infected with prion diseases (such Creutzfeldt-Jakob Disease) which transfered to cattle when they ate the feed.
You are what you eat, I guess...
Luckily the practice of feeding offal to livestock has been stopped and incidences of BSE have fallen dramatically.