Nothing to do with puppies being shipped from shelter to shelter.  I see puppies in shelters across the country on my newsfeed.  They get it the old fashioned way, in over-crowded kill shelters, before they are pulled.
Typically they are pulled when it is discovered that they are sick, as they will be killed otherwise, or when exposed for the same reason, or they are pulled and go into a foster home and are discovered to be ill at that point.
From there they go into a hospital/quarantine setting until well enough to go to a foster equipped to deal with them, and are then quarantined until a vet gives the all-clear.