Id hazard a guess that live virus contact with people on scale is what — by chance — eventually selects a cross over strain.
So virus that can be cultured into existence of out of milk presents a possible vector for that. Hence they are testing to see if they can grow the virus from milk samples.
So virus that can be cultured into existence of out of milk presents a possible vector for that. Hence they are testing to see if they can grow the virus from milk samples.