It doesn't matter where the cow came from! what matters is how and when this cow got sick. Could it have gotten sick in the US? or was it infected in Can, before being shipped to the US? Unfortunatly no one knows these answers. a lot of work will have to be done to root out the problems if they ever do find the cause. In the mean time its best not to throw rocks, as they could bounce back and hit you in the head.