Why is my dog's fur itching and thinning out?

I have a 3 year old black mouth cur. Before this, she was, and in every other sense still is a very healthy and active dog. She has short brown fur. About a week ago I noticed the fur on her sides and back thinning out. Apparently it's itchy because she scratches at it. I have a Rhodesian Ridgeback mix(also has short brown fur) in the house with her. They always play and interact with each other but he has not been affected by this at all. Any ideas on what this may be?

she has aids...

Could be Seasonal Flank Alopecia: http://www.veterinarypartner.com/Content.plx?P=A&A=2965&S=1I would make a vet appointment though to rule out things like mites, fleas (which you don't always see with the naked eye!), bacterial and fungal infections, or an immune-mediated disease.

What you describe sounds like it could be a case of mange. Mange is a skin condition caused by tiny mites that you can't see with the naked eye. There are three types of mites that attack dogs most often: demodectic (not contagious and may itch or not), sarcoptic (very contagious and extremely itchy) and cheyletiella (contagious and mildly itchy). Vets can do a deep skin scraping to detect the presence and type of mite. Regardless of the type of mange, in order to cure it you need to treat with a medication that kills the mites.The mange medications most often prescribed by vets contain toxic chemicals that will harm your dog sooner or later. These are Ivermectin (also known as Ivomec) and Amitraz (also known as Mitaban). See the links that follow for toxicology information. It is always advisable to check the veterinary drug database for side effects of any medication prescribed by your vet http://www.drugs.com/vet/ Thankfully, there are a number of effective alternative treatments out there that are safe and natural at a reasonable cost that will kill the mites. You can easily do some research in the Internet to find out about these and compare your options.I prefer the 'spray type' because it is inexpensive, very effective so it works fast, convenient to use (no mixing and no mess), and it is natural and harmless to pets and humans.Hope this helps.Toxicity:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1481314/?page=1http://www.drugs.com/sfx/ivermectin-side-effects.htmlhttp://www.petmd.com/dog/conditions/toxicity/c_dg_ivermectin_toxicity\http://www.drugs.com/vet/mitaban.htmlhttp://www.petmanage.com/dog-health/what-is-amitraz-toxicity.htmlMange spray:http://www.florapetnaturals.com/online-store.html