Important Information…the advice I am providing is solely based on the information you are giving me. To accurately diagnose and treat a patient, a veterinary doctor-patient relationship is required. Before I can tell you what is wrong, I must see you pet and perform an examination. Over the internet, your description may be misleading and you may not see what a trained veterinarian would see. Therefore, the advice I give you is not to be taken as 100% accurate. I can tell you how I have treated cases in the past with similar symptoms and you must make a decision whether you want to follow my advice or not. This service is not a substitute for visiting your vet. With that in mind, let us start…
Depending upon what type of fly placed its eggs in the dogs skin wound, you are looking at a maggot or fly larvae. The dog could have had a small wound and the flies lay eggs in the tissue. Some of these larvae can be an inch or so in length and 1/4 inch thick.
What you should do is clean the area with hydrogen peroxide and try to flush it out with a chlorhexidine solution. If the dog will allow, you can try to probe the wound with a tweezer to make sure no more larvae are in there.
A visit to the vet would be recommended to follow up and perhaps antibiotics are indicated.
Your dog probably has a heavy coat and under the coat, the skin could become infected due to moisture and bacteria. This is a perfect medium for the parasites.
Here is a link that may help explain in more detail. I must caution you that I have not reviewed this link and unless it is written by a veterinarian, the information can't be held to be medically accurate. But just to give you information that might help here it is:
One type of fly is called Cuterebra http://www.vin.com/WebLink.plx?URL=http://botfly.ifas.ufl.edu/links/links1.htm
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