Because prion diseases lack immunological involvement in host animals, for human infection with the BSE agent infants and children are not likely to be more susceptible than adults similarly, hospital patients, pregnant women and people taking immunosuppressive drugs would not be expected to have a greater risk. With the exception of brain and spinal cord, and more recently, the retina, all other tissues and secretions from confirmed BSE cattle have failed to transmit the disease when either injected into or fed to mice. In particular, milk and beef meat have not caused the disease in experimentally infected animals. Prior to the 1989 SBO ban in Great Britain, some 446,000 BSE-infected animals likely entered the food chain and were consumed. Infectivity seems about the same for BSE when administered to mice.
Actual exposure remains an open, and perhaps unanswerable, question.