Strains of BSE

There is increasing evidence that there are different strains of BSE: the typical or classic BSE strain responsible for the outbreak in the United Kingdom and two atypical strains (H and L strains).

Classic BSE Strain

The BSE strain responsible for most of the BSE cases in Canada is the same classic or typical strain linked to the outbreak in the United Kingdom. It is known to be preventable through elimination of BSE contaminated feed and has been causally linked to vCJD in humans. This typical strain has not yet been identified in any U.S.-born cattle.

All five of the U.S.-born BSE cases and two of the 20 Canadian-born BSE cases were caused by atypical BSE strains. Of these seven North American cases, four were linked to an atypical BSE strain known as the H-type. and three were identified as the L-type. The strain type for the other three older North American cases, a 13-year-old BSE-infected Canadian cow, a 10-year-old BSE-infected U.S. cow, and an 11-year- old BSE-infected U.S. cow, have been identified as the L-type.


Atypical Bovine Spongiform Encephalopathies, France, 2001–2007

Past Meeting Materials, Transmissible Spongiform Encephalopathies Advisory Committeeexternal icon (Note: The Transmissible Spongiform Encephalopathies Advisory Committee was terminated on June 9, 2016external icon.)