Maybe… Prions are a different beast altogether in terms of illness. Even the most terrifying forms take years to debilitate and kill you. I don’t think most countries want to wait that long to cripple an opponent, and definitely won’t want to unleash anything on a neighbor that will certainly come back at them. Right now the only thing that truly gets prions to be gone is incineration levels of heat.

So I don’t think biological warfare is going to be on the table. Maybe terrorist type attacks, where the asymmetrical nature of the opponents makes the user unconcerned about potential effects on themself.