I'm not sure exactly what you're asking. One of the things we're concerned about is that the biosecurity aspect is preventing movement of things onto the facility that aren't there or letting them spread within a facility. A pathogen or an infectious agent will come into the facility through various routes. That could be people coming in, such as farmers, veterinarians, visitors and people bringing in feed, or it could be other animals brought into the facility, to the farm. It could be wild birds. It could be things that come in through air, which is very unlikely, but it's in close proximity. It could be things that get in through water, through runoff from pastures. There are various ways things can get in.
The relative risk of those will vary greatly with the type of animal, the type of farm and the pathogen we're talking about, but something that is new has to get onto the farm, typically, for us to be worried about a biosecurity concern.