British Columbia: Fern freakout. HELP!

It started with my enormous sword fern. It had been healthy for years, but towards the end of last year I noticed some evidence of something nibbling at a few leaflets, but the damage was minimal.
This year, very soon after the fronds opened, there was a LOT of damage, first on a few leaflets, now on about 80% of the fern. Each leaflet, all the way down the frond, looks as if an insect has been taking bites out of it, and the "bitemark" is bordered by a yellowing/browning effect, which makes me think it could actually be a disease rather than an insect. The overall result is each leaflet is about 1/3 the size it should be, and the whole plant looks distorted.
Even worse, this has spread to a second sword fern on the other side of the garden, a deer fern, and now a Japanese painted fern and I think my autumn fern is infected too. Local nurseries are dumbfounded.
Has anyone else experienced anything like this?