question about mice scabbing

Question
My pet black mouse has been having a rough time, when I adopted him from PETCO, my friend who works with animals came to look at him after my concerns with his sniffly sneezes.  I treated him with amoxicillin and it seemed to help but then the infection spread to the other mice. I'm pretty sure it's not an allergy, but he does still have trouble breathing and is only half the size of a normal mouse. I took him out of his cage and found a lot of scabbing [I had noticed one scab after adoption but didn't think anything of it, since he was living with others] but now there's a cluster of different scabs. What could this be? An allergy to something? Thanks for your input.
Felicia

Answer
Hi Felicia,

Since it seems to have spread to the other mice, the sneezing is likely not a result of an allergy.  Black mice have a tendency to be slightly smaller than most other mice, but if he seems a great deal smaller, he may have been a runt.  Runts sometimes catch up in growth, but can often suffer compromised immune systems (and sometimes otherwise normal mice are slowed in normal growth because of illness, after all, being sick takes quite a bit of energy).  This may make recovering from the sneezes (respiratory infection) more difficult for him, and he'll need to be isolated from all others and in another room if possible to prevent him from relapsing.

This same immune deficiency that makes it harder for him to handle the respiratory problem may also make it more difficult for his body to ward off normal mite populations, which may be causing the scabbing (though it is difficult to tell for sure if this is the case without a vet visit).  You can help reduce the mites he's exposed to by treating him temporarily with a mite spray (http://en.allexperts.com/q/Mice-3824/2008/10/red-skin-hair-loss.htm), cleaning his cage and all toys thoroughly, and freezing his new bedding for 24 hours before using it.  Other possible causes of scabbing could be a contact or food allergy (try changing the bedding and see if that helps, and then try changing the food) or a fungal infection like ringworm.  Ringworm is transferrable to you and to other mice, so if you suspect this may be the case, bring him into a vet and ask them to diagnose it.  They can then give you an oral or topical antifungal medication for him and anyone it may have been passed to.  The last possibility is an itchy bacterial infection from his previous wound, if it came from being picked on.  The antibiotics should help, and you can keep the scabs clean by dabbing a small amount of neosporin on them a couple of times a day (don't use too much - most of it will wind up in his tummy!).  You can try placing a rock or other hard surface under his water bottle so he trims his own nails when he goes to take a drink - this way he may do a little less damage if he scratches at the scabs.

Best of luck!
-Tam