...Some folk have watered, fed and/or sprayed and the plants seem to have produced new, healthy growth.
If the plants are producing new healthy growth, then it's not a virus. Once a virus is in the plant, it can't be cured, there isn't any way to get rid of the virus. I don't think it's a virus.
Have you closely examined the plants, uncurling the leaves and looking for aphids?
The leaves look healthy enough apart from the curling, and puckering, so it looks like aphid damage to me on first glance. Herbicides can cause leaf rolling, but it's have to be a widespread drift to catch the plants that are inside greenhouses. Normally you'd see pleanty of yellowing, too.
Sometimes sites near railway lines suffer in this way because the rail companies often spray along the lines to keep weeds down.