Okay. I am ignorant of search methods, etc., when a plane disappears, and I know zip of the weather in the area. Any chance it's "just" underwater somewhere?
(I suspect that if it had been spreading anthrax post-disappearance, the casualty count even a few hours later would be higher than one. If it's higher than one by the time I send this, disregard this parenthetical remark.)
Supposedly, the aerosol produced by a crop duster would be insufficiently fine to deliver the anthrax very effectively. It may well be that the terrorists have already shot their wad, and the casualties will be fairly low. We shall see.