The three most common ways it is transferred is through direct contact with wild birds, contact with feces from wild birds, and on a care-taker's shoes and clothing. It can also be spread through mammals that are carrying the virus particles. I'm currently running a research trial with laying hens, and it is such a huge concern for my work that when I enter the house I step into a dry bleach footbath, then change shoes, put on coveralls, and spray myself down with Lysol. Commercial flocks are even more strict as most have shower-in-shower-out facilities with clothing that is only ever worn in the barn, and unfortunately they still have had issues with their birds catching it. It's that contagious. Think of how easily Covid was spread in the first few months we were dealing with it; this is basically the bird equivalent.
