Help with scabs around vent

[maggot67]

I am losing my Araucana chicken with a problem around her vent which I can't identify. Will try & work out how to put picture in. She has had these huge ulcerated scabs for about 3 weeks. Have been to the vet who was also not sure what it was. Has been suggested that it could be a form of Fowl Pox but she has no lesions at all on her comb or head. She is eating well but losing weight trying to fight this. She has been treated for mites etc with Dectomax & is on Amoxycare antibiotics. I have sprayed affected areas with iodine skin spray. None of this seems to be working & I don't know what else to try as I don't know what I am treating.
Anybody out there know what it might be or seen anything like this before?
Lou

 

[CoopCrazy]

Sorry but your pic did not come thru... If you can get one on here it will help alot...