I don't know. I tried to find more info below.
Anthrax is very rare in the United States and in other countries where animals are inspected before and after slaughter.
Sterilise wool, hair, hides and other infected products by ethylene oxide gas or ionising (gamma) radiation.
Meanwhile the first commercial irradiator was used in the 1960s to kill any lingering anthrax germs in lambs wool sweaters.
Didn't really find an answer to your question nor did I confirm that irradiation is always in use.