Rescued mouse

Question
QUESTION: We found (what we thought was) a baby mouse, squirming around in the rain on the sidewalk about a week and a half ago (October 9). We brought it inside and dried it very carefully with a blow drier, then put it in a box with some old t-shirt to keep it warm, and some milk mixed with sugar. After reading a bit about baby mice, we got some puppy formula for it, and it is now eating solid food (mostly oats and cucumber). It has grown quite a bit and has become more active.
After an unsuccessful attempt at releasing it, we are thinking about keeping it, but have some questions.
We're not sure what type of mouse it is, first of all. Is there a way you could tell by looking at the photos posted below?    
We were wondering if there are any dangers to keeping a wild mouse like this in our house.  In addition, we've heard that mice can get lonely and depressed when living alone.  If that is the case, would it be safe to introduce a fancy mouse into this mouse's habitat?


This is what it looked like the day we picked it up:
http://i183.photobucket.com/albums/x147/cargb/pentax/andersandcathlin/mouse/2007

This is what it looks like now:
http://i183.photobucket.com/albums/x147/cargb/pentax/andersandcathlin/mouse/2007

Thank you very much in advance.

ANSWER: Thank you for the photos, they are very helpful. You have a deer mouse, approximately 4 weeks old. He looks adorable!

It sounds like you are a natural, wild mice do not usually survive in captivity especially when they are babies. Formula is the next best thing for mouse milk though not a substitute. Your mouse probably won't live as long and may be weaker. However, deer mice are the longest living of small rodents (up to 5 years).

I have read that if you live in the San Diego region deer mice may carry the Hantavirus. Mice aren't effected by this illness but humans are.

Mice are social creatures and thrive in communities. However, if you introduced another mouse you would have to be sure of the sex of each mouse or they will reproduce. I wouldn't suggest introducing a fancy mouse as a buddy because the deer mouse may have diseases immune to wild mice but not to fancy mice. Also their behavior would be unpredictable. I think it would be safer if you gave him lots of attention instead (unless you find another deer mouse).

As pets, deer mice are active intelligent and don't usually bite. However they are not as easy to tame as fancy mice.

In the wild they eat insects and berries so be sure to include small portions of cooked meat and fruit in their diet. Mice also love seeds, nuts, stale bread, peanut butter, fromage frais (great if they aren't feeling well), veg, pasta, rice and crackers.

Make sure the cage is escape-proof. Wild mice are good at escaping and remember they can chew through wood. They like wheels, tubes (toilet rolls are great), ladders, branches (make sure they haven't been sprayed with chemicals)and lots of hiding places.

Please feel free to ask any more questions. Good luck

---------- FOLLOW-UP ----------

QUESTION: Hi again. First, thank you so much for getting back to us so quickly! We've called a vet to see if there is anything we can do about testing the mouse for Hantavirus before we commit to keeping it. We're also looking into buying a small, glass fish tank to keep him in, if he does stay (very escape-proof!).
I have another question for you, though.  
Since our unsuccessful release attempt on Tuesday, the mouse has been acting a little strange. He (or she, we're not sure) has been squeaking loudly and frequently, while at the same time pawing at his genital area.  We noticed that his anus looks swollen and irritated, and once or twice I've actually seen him pulling feces out (I know this is slightly gross, sorry!).  He's still eating, drinking and running around as much as ever, so it doesn't seem like a huge problem, but it also doesn't seem quite right.  We've taken the oats out of his dish and given him some cut up plum and water instead.
I did some reading and found out that rats get a common affliction called megacolon, which sounds an awful lot like what our mouse is dealing with. Is it possible for mice to get this? Do you have any other suggestions on what the problem could be, or how else we can help him?

Thanks again!

Answer
It's not gross don't worry, I've heard a lot worse!

It sounds like he is constipated. It's probably because he has not has a balanced diet. His poop should be brown and small. You should be able to pick them up but they should feel soft and slightly moist when fresh. They should not be shriveled, unusually shaped or smell bad.  The best remedy is fruit and veg. This also may be why is has a swollen anus.

I have never has a mouse with megeacolon (I have had over 200 mice) but thats not to say mice don't have this condition, especially wild mice.

The important thing is to get him eating a balanced diet of mouse or hamster food. Then the problem may sort itself out.  I wouldn't worry, it's a good sign that he is Playing, eating, drinking and its coming out the other end.

Please feel free to ask any more questions, all the best.