Didn't they trace the 'jump' of this virus to the actual first horse where it occurred? Seem I remember reading that.
My classmate was the veterinarian that took care of the dogs at that dog track near Ft. Myers...he called me and described to me what at first looked to be a really mean case of Bordetella... that was spreading thru the track dogs...but couldn't isolate the bacteria on dogs that had died...necropsy and virological studies recovered the virus and by the time it was realized the virus had spread....
I know of veterinary clinics that have had to shut down operations for about a week to allow the virus to run its course in those clinics....so hopefully the H5N1 won't get loose like this H3N1 did...