complex mouse health issues

Question
Ok I have had a mouse for a very long time and then my dad thought i should get a friend for her so we got one, but not from petco, from a pet shop. And this mouse had a small scab on its rear that the lady said was a bite. Then two days later i noticed my first mouse had scratched a hole through her ear so i called the vet and he got her some antibiotic medication. Now, two weeks later, she has torn her ear completley in half and has a deep sore behind it, also losing hair and the other ear is bloody. I just tonight noticed that the small scab on the petshop mouse is actually a very large hard mass running the legnth of her back that actually is raised up with some yellow looking skin underneath. It is hard like a scab, not a tumor, and i didnt notice before because it has hair covering it just like the rest of her. I am really freaking out and do not want either animal in pain. Any suggestions or ideas of what this may be?  

Answer
Dear Chelsea,

Both mice should go to the vet right away.  This sounds pretty serious.

The new mouse sounds like she has a bad infection, but I can't be sure, not being a vet or seeing the mouse.  The old mouse likely has mites (from the new mouse), but it could be something more serious.  For instance, the new mouse may have a fungal infection, such as ringworm, that she gave to the other.  Even you can get ringworm from a mouse.

Never buy a mouse from a cage with sick or wounded animals in it, never buy a sick or wounded mouse, and never buy from a pet store that seems to neglect its mice or other animals.  

I hope both mice are ok soon.  best of luck.

squeaks,

Natasha