All the animal and human TSE's have been shown to be transmissible experimentally to laboratory animals. The human and animal diseases are pathologically similar and share some etiological similarities. TSE's are not officially considered zoonotic diseases, i.e., known to be naturally transmissible from animals to humans. The distribution of CJD in the world does not coincide with that of scrapie in sheep or of BSE in cattle. Human exposure to sheep or cattle has a low correlation with CJD. However, the recent report from the United Kingdom of nv-CJD, and its possible relationship to BSE, is causing scientists around the world including those at CDC to reevaluate whether BSE may be a zoonotic disease.

This concern is further supported by the recent report of experimental BSE transmission to macaques, with the development of nv-CJD-like plaques in these monkeys.

The possibility of transmission of TSE's from animals to humans has been suggested, most recently in connection with the identification of nv-CJD in the United Kingdom. Scientists in the United Kingdom concluded that the nv-CJD cases may be unique to the United Kingdom, raising the possibility that they are causally linked to BSE. The scientists stated that ``the common neuropathological picture may indicate infection by a common strain of the causative agent, as in sheep scrapie in which strains of the disease have been identified.