Susceptibility of cattle to the agent of chronic wasting disease from elk after intracranial inoculation.

Cattle could be exposed to the agent of chronic wasting disease (CWD) through contact with infected farmed or free-ranging cervids or exposure to contaminated premises. The purpose of the current study was to assess the potential for CWD derived from elk to transmit to cattle after intracranial inoculation. Calves (n = 14) were inoculated with brain homogenate derived from elk with CWD to determine the potential for transmission and to define the clinicopathologic features of disease. Cattle were necropsied if clinical signs occurred or at the end of the study (49 months postinoculation; MPI). Clinical signs of poor appetite, weight loss, circling, and bruxism occurred in 2 cattle (14%) at 16 and 17 MPI, respectively. Accumulation of abnormal prion protein (PrP(Sc)) occurred in only the 2 clinically affected cattle and was confined to the central nervous system, with the most prominent immunoreactivity in midbrain, brainstem, and hippocampus with lesser immunoreactivity in the cervical spinal cord. The rate of transmission was lower than in cattle inoculated with CWD derived from mule deer (38%) or white-tailed deer (86%). Additional studies are required to fully assess the potential for cattle to develop CWD through a more natural route of exposure, but a low rate of transmission after intracranial inoculation suggests that risk of transmission through other routes is low. A critical finding is that if CWD did transmit to exposed cattle, currently used diagnostic techniques would detect and differentiate it from other prion diseases in cattle based on absence of spongiform change, distinct pattern of PrP(Sc) deposition, and unique molecular profile.