Mad Cow Disease (cont.)
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BSE Cases Identified in Canadian-born Cattle
As of February 18, 2015, 20 BSE cases in Canadian-born cattle have been identified, 19 in Canada and 1 in the U.S. Of these 20 cases, 14 were known to have been born after the implementation of the 1997 Canadian feed ban ; 13 of these 14 were born after March 1, 1999. (See Figure above: BSE Cases in North America, by Year and Country of Death, 1993-02/2015). This latter date is particularly relevant to the U.S. because since a USDA rule went into effect on November 19, 2007, Canadian cattle born on or after March 1, 1999 have been legally imported into this country for any use. One of the 20 Canadian-born BSE cases was reported in an animal that was most likely born before or possibly very shortly after implementation of the 1997 feed ban. Based on the known or most likely year of birth, an average of 1.4 cases of BSE occurred among the group of animals born each year in Canada from 1991 through 2004. The highest reported number of cases by birth year in a single year, 3 BSE cases, occurred in 2000, 2001 and 2002. The most recently reported case extends the period of BSE transmission in Canada through at least the early half of 2009.
Strains of BSE
There is increasing evidence that there are different strains of BSE: the typical BSE strain responsible for the outbreak in the United Kingdom and two atypical strains (H and L strains).
All (3) of the U.S.-born BSE cases and two of the 20 Canadian-born BSE cases were 10 years of age or older and caused by atypical BSE strains. Of these 5 older North American cases, 3 were linked to an atypical BSE strain known as the H-type. The strain type for the other two older North American cases, a 13-year-old BSE-infected Canadian cow and a 10-year-old BSE-infected US cow, have been identified as the L-type.
Medically Reviewed by a Doctor on 2/19/2015
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