Posted: October 5, 2009, 5 p.m. EDT
Q: I am worried about my pet mouse. He is 10 months old and lives with his brother in a big, clean cage. They do not fight at all, but a while ago he started losing patches of fur, with no obvious scratching or redness. Eventually the fur grows back, but new patches appear all the time. He is still eating and acting normally, and his more dominant brother has not lost any hair. Do you know what this could be? If it is mites, fleas or a fungal infection, how do I treat it?
A: It is difficult to know what is wrong with your mouse without looking at him. Ectoparasites like lice and mites are a likely cause, but skin fungal infections also can occur. You mention both, and I believe you are on the right track. Even though his brother is not showing similar symptoms, it still does not rule out these infectious problems.
Both skin problems, ectoparasites and fungal infections, can occur in older mice as a secondary problem due to an impaired immune system. Therefore, your mouse may have a primary problem and the hair loss is secondary.
The only way to know for certain what is causing the hair loss is to visit a veterinarian. A simple culture can be performed for the fungal infection, and ectoparasites are easily seen under a microscope.
No over-the-counter products exist that are labeled for mice for either problem. Again, this is another reason to visit the veterinarian. Your veterinarian can prescribe medication that is proven safe.
See all of Dr. Rosenthal's Critter Q&A articles>>