I am sorry to hear that your boy has been licking and scratching. There are a few possibilities as to the cause of this problem ranging from allergies to skin parasites to bacterial or yeast infections! The sores are due to a skin infection, this is usually secondary to another problem that has caused the itching in the first place (such as allergy). Unfortunately, wthout antiinflammatory medication to stop the itching he will continue to scratch and make the sores worse, which will then get even more itchy - it is a vicious cycle that really requires a trip to your Vet to obtain some medication (such as prednisone).
The skin scraping is done primarily to check for mites (Demodex and Sarcoptes) which cab be rulled out if this was negative and it is a good place to start.
Firstly - you need to make sure that your dog is definitely up to date with flea control. Make sure you are using a flea product appropriate for his weight. Even though you cannot see any fleas on him doesn't mean there aren't one or two lurking and oftentimes this is all it takes for a dog with flea allergy dermatitis. These dogs are allergic to the flea’s saliva so it only takes one flea to bite to set off the allergic response. You may also need to flea bomb your home.
He may have an underlying allergy of some sort with secondary infection; however this itchiness could also be caused by parasites or fungi (ringworm or yeast). Basically dogs are allergic to four main things - food, fleas, grasses/plants (contact allergy) or environmental allergens (canine atopy - the dog version of eczema). I am sure you have worked through all of these with your Veterinarian, but I always like to ensure I have talked through each of these with my clients here in New Zealand. Flea allergies are avoided by strict flea control - every 3 - 4 weeks with Advantage or Advocate or every 7- 8 weeks with Frontline. You must also ensure all dogs and especially cats, in the household are treated at the same time.
To rule out a food allergy, you need to undertake a food trial with a 'hydrolysed protein' diet such as Hill's Z/D ultra allergen free and this needs to be fed SOLELY for 3 weeks minimum to see a response. Dogs commonly develop intolerance to a diet they have been fed for a long time, so a diet change is not a necessary precursor. After this time if you are seeing a change in your dog's allergy you can slowly introduce different foods week by week with the guidance of your Veterinarian.
Contact allergies are best treated by avoidance of the plants that are to blame, but identifying the exact cause of a contact allergy can be very hard. A referral to a canine skin specialist may be the way to go in your dog's case for either a skin patch test or a blood allergen test.
The next step would be to double check for fungal disease (such as ringworm) and there are several tests for this including a UV light and a fungal culture. It could also be that your dog has a bad yeast problem - and a good medicated shampoo such as Malaseb may well do the trick! Again a full Vet check will be able to confirm or deny this. If after these tests there is no diagnosis, the next step would be to carry out a food trial as above.
There are a few things you can do in the meantime to help alleviate his itching:
- a medicated shampoo that will deal with both yeast and bacteria - Malaseb (or a similar product containing Chlorhexidine and Miconazole, rather than the natural oatmeal shampoo). This requires you to make a lather and leave this lather on for 10 minutes before washing off! For many clients this is easier said than done, but it is SO important.
- if only a small area is affected you can apply Neosporin cream sparingly twice per day.
However, it is very important for all skin problems to determine the cause before further treatment is begun.
Hope this helps,