Wounds and itching, but no bugs

Question
My mouse is about a year and a half old.    She had a cage mate, but I recently had to put her down due to a very large tumor. Since I put here cage mate down about a month ago my mouse I have now has developed red, open sores, and is almost constantly scratching.
She has a small bump on the top of her head right in the center, but then it disappeared and she developed another one on her back. They are not tumors. They are only small bumps, almost like a bug bite. I have given her many baths, and no bugs are to found.
I called a vet and she said that mites do not just show up out of no where either so, this is not a sort of bug. I don't believe it to be an allergy either because I have not changed the type of bedding I use (Carefresh) or her food. The vet said that sometimes sores and scratching can develop after a mouse loses her cage mate, and I was wondering if this is trtue, and if so, how do I help my poor little Aedan?

Answer
Hi Rachel,
   
Your vet should be able to do a skin scrape and look under a microscope to be sure of the cause of the itching, which is the only way to be sure what the problem is.  Different causes will require different treatments, so let me explain the normal causes of itchiness:
   
Mites are, in my experience, the number one cause of itchiness, scabbing, and sores around the head, neck, shoulders, and even the front arms.  Usually they stick to these regions, but in bad cases, hair loss and itchiness can extend down the back.  Mites are actually very tiny and it's highly unlikely you'd be able to spot them with the naked eye.  They also frequently come in on beddings such as carefresh (no bedding is guaranteed to be pest-free because of shipping and storage) - a great way to prevent this is to freeze all bedding for at least 24 hours before you use it, which will kill any little hitch-hikers.  Mites are easy to kill using an inexpensive mite spray from your local pet store, and instructions are here:  http://en.allexperts.com/q/Mice-3824/2008/10/red-skin-hair-loss.htm

The reason I'm bringing up mites even though you and your vet are pretty sure it isn't, is because mites are typically present in small amounts on most mice and are managed by friendly grooming of one another.  Therefore, since she has just lost her buddy, it could definitely be possible that between her grief (and possible lack of frequent self-grooming as a result) and the fact that there isn't another mouse there now to groom her and keep her mite-free, she could now be having trouble controlling them and needs to be treated.  Remember, if you treat for mites, treat at least two times (following the label) and thoroughly wash everything in the cage, throwing out anything absorbent that could harbor them.

There's also the possibility of other skin diseases or parasites, like ringworm - a fungus which can be transferred to you and is treatable with antifungal medications, or even an allergy (which can be caused by longterm exposure to things, too, so I wouldn't rule it out because of no recent changes).  I would try to rule out all other possible causes besides allergies first, as testing for allergies is difficult and time consuming.  If you are sure it's allergies, you can make the environment as allergen-free as possible (aspen bedding, oats for food, no edible toys or any kinds of treats).  If symptoms go away, you can start introducing things again one by one to the diet or the environment until you see a reaction.

These are all of the things I know of that can cause skin problems, so if it's definitely none of the above, I'd guess stress.  Sometimes stress can cause a mouse to act self-destructively (but not usually, I really would try for mites first).  There isn't a whole lot you can do for that, though, as it wouldn't be wise to get her a new friend until she is all healed up.  The most important thing in any case is to keep any spots where the skin has been broken or is irritated clean.  You can add betadine (pet-safe iodine formula you can find at your local general store or pharmacy) to warm water until it's the color of tea and dab it over any wounds to disinfect it, and can keep it clean by applying a small amount of triple antibiotic ointment, like Neosporin.  Neosporin is safe, but keep in mind that she'll probably be licking most of it off, so you only need a tiny bit to keep her from eating a bunch.  Remember to keep everything away from her eyes.

Lastly - the bumps!  Bumps could be tiny infections or abscesses under the skin that result from bacteria getting in open wounds.  Abscesses definitely aren't uncommon but can become serious, so keeping open injuries clean is very important.  An abscess doesn't have to be a huge lump, so if they are coming and going, I have a hunch it's from the scratching causing infections.

Sorry that was so long!  There are a lot of potential causes, and it's tough to rule any of them out without first trying to treat for them (or doing a skin scrape).  Best of luck to Aedan (beautiful name!), and I hope she feels less itchy soon!

-Tam