Epidemiological studies of the outbreak of BSE in the United Kingdom, including a computer simulation of the BSE epidemic, have characterized it as an extended common-source epidemic. Each case has been considered a primary case resulting from exposure to a single common source of infection. It is believed in the United Kingdom that rendered feed ingredients contaminated with scrapie infected sheep, or cattle with a previously unidentified TSE, served as the common source of infection. One study demonstrated that meat and bone meal could be incorporated into cattle feed in sufficient quantity to transmit BSE to some of the animals that consumed the feed. Thus far, other research including research by USDA has not confirmed that the feeding of U.S.-origin scrapie-infected feed ingredients to cattle produces BSE. Therefore, the theory that BSE evolved naturally in cattle has not been ruled out.

Furthermore, the U.K. studies suggest that the spread of BSE appeared to have been exacerbated by the practice of feeding ingredients from rendered BSE-infected cattle to cattle, including young calves, a practice that was subsequently banned. Incomplete immediate compliance with the feeding ban may account for the fact that some cattle born after the ban continue to be infected with BSE and has complicated any theory of vertical transmission of the disease. The research findings of maternal transmission of BSE are inconclusive, but if it occurs, it does so at a rate insufficient to maintain the epidemic.