Yes - different lice!!!

I found that out last year Decto treats sucking lice, but not Biting lice(which is what mine had last year after dectomaxing (I even looked under the microscope at the vets to see - grizzely little buggers!).
I really appreciate the inputs and appreciate (as I'm sure we all do), that it is opinion based on our experiences, not a true diagnosis. The main thing is, that from all thats been said - I'm pretty sure its not Scab. If its biting lice - Ive got em with the crovect, if its the other I'll keep an eye and get a scrape done if not getting any better. Yes to whispy shreds, no to any facial probs , although the wool loss does present exactly as you've described shep). Lice is still a suspect, but I dont remember such dry baldness last year, so will keep a very close eye thanks. Another disease brought onto my 'radar' - Thanks again all