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Mice/What's Wrong With My Mouse?


About a week and a half ago, I noticed one of my mice acting lethargic -- moving slowly, breathing heavy, shaking a bit when it walked, not wanting to eat or drink, and going off by itself. Later that day, she seemed to get her appetite back and she was back to her normal self. Three days later, the lethargy came back as well as the lost of appetite. Again, by the end of the day or the next day she was back to her normal self. Another three days later though the lethargy returned so I took her to the vet. The vet said although she doesn't see any discharge from her nose she thinks it could be mycoplasma pulmonis. She prescribed 10 days of Baytril and 3 days of an anti-inflammatory. At first my mouse seemed to respond well to it but it was the same pattern -- doing well for 3 days, etc.

She is housed with 3 other mice who get along well and none of which exhibit the same symptoms. I only use dust-free bedding made from recycled phone books.

When I hold her to give her the medicine, she poops (as do all of my mice because they don't want to be held) and it is sometimes very hard.

She still has 4 days of Baytril left after I gave her today's dosage. Should I take her back to the vet?

What could be wrong???

Hi Paige,

If she is still having her symptoms now, at the end of her round of antibiotics, I would give your vet a call.  Your bedding sounds great, so I don't think that is the problem.

Mycoplasma is a definite possibility, as are a few other potential infections, if it is respiratory.  You don't mention sneezing, wheezing, rattling, or coughing - does she have any respiratory symptoms you didn't mention?  Myco attacks the lungs, so I would think she would be showing something like that, but I am not a veterinarian.  The thing with myco is that many if not all mice and rats have or are exposed to it, whereas some tend to get more sick than others who might have an infection but not show any symptoms.  This could explain why the other mice aren't currently showing symptoms, but she is.  Not only does myco make mice sick, but it also depresses the immune and respiratory systems enough that it is very easy to get secondary infections that may not respond to antibiotics, such as viruses.  Your vet may decide to try a second antibiotic such as tetracycline (which can be mixed with water, so may be easier for her to take) to try to suppress the infection before it affects her too seriously, so it is a good idea to ask them how they would like to proceed.

Definitely keep an eye on the other three mice to be sure that none of them start showing symptoms over time.  The good news is that you don't need to separate her as long as they get along, since they have all already been exposed to anything she may have.  This is another good reason to ask your vet about tetracycline or other antibiotics that can be provided in the water, so that all of the mice can be afforded that potential protection, if it is in fact something contagious.

The last possibility would be if something else was wrong with her.  Lethargy, loss of appetite, and shaky movements are all signs of discomfort, so it could be that something else internal is bothering her, such as an injury that might be tough to see, a congenital issue, etc.  It may be worth asking your vet at the same time if they think this may be a possibility, and how to provide comfort and care if so.

The three days of normal behavior at a time is very odd, so please let me know what your vet says!  I am curious to know, and my fingers are crossed for her to feel better soon!

Best wishes,


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I have enjoyed the companionship of mice nonstop since 2004, and spent a year caring for them in a lab where I learned a great deal about their breeding, social needs, and health. I spent a few years breeding them, specifically working with albinos, marked mice, angora mice, and satins. My education never stopped - I am learning something new every day from current and well-established research thanks to the wonderful folks at the Jackson Laboratory, as well as from my wonderful mousey friends online. I also love learning from my terrific questioners here on AllExperts - you folks keep my passion for these amazing animals alive and well!

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