my pet mouse encountered wild mice

Question
Hi There Tamarah

I purchased a mouse for my children some time ago now, he is stil alive and well. I am not sure what breed he is, he is grey in colour with red eyes. His name is Juarez, yes, like the female guinea pig off G Force.

Since having him, after 4-5 months, we seem to have a stray mouse from outside move into our home. These mice are darkish brown with dark coloured eyes, possibly black? Could keeping him outside have attracted the new mice here?

Today while smoking outside i noticed something jumping around in Juarez's cage, i thought it was a cricket at first, til i got a little closer, it was a younger mouse climbing around and eating his food in his cage. I was amazed at how it couldve gotten in there. Juarez was very curious of the little mouse in his cage. The little mouse, was very scared, and i thought was a baby as the gaps between our cage is approx 1cm wide.  

My main concern here is, can our pet mouse contract any sort of infectious disease from encountering these mice, im very sure they are field mice, could Juarez have mated with a female through his cage and created these young mice? We dont live in the countryside. We are also located in Auckland, New Zealand if this may help answer my question.

Sorry for such long question.

Thank you very much in advance :)

Answer
Hi Kelly,

If you purchased him, he's almost certainly a house mouse.  Mice don't really have breeds, but they do have different names for their coloration.  Since he has red/pink eyes and grey fur, he'd be called a lilac or a dove, depending on local naming standards.  :)

Since he's a different species than the wild mice, I can't tell you whether or not they would or could breed, but it would take three weeks for babies to come along and the mother doesn't usually stick around dad after the fact, so I believe the chances of him mating through the cages is limited (though I can't promise it's impossible).  I also can't guess at whether or not he attracted mice to your home, or if they were present in your area to begin with and are just coming out of the woodwork recently (I'm not familiar with your area, but many factors including the environment would affect local species).  However the little mouse got in your little guy's cage, it would be safer to keep all critters out besides your pet.  Although that won't eliminate all disease risks, it will at least keep animals bigger than ideally 1/4 an inch in circumference from getting inside and harassing your little guy (including snakes!  I HAVE had snakes get inside wire cages!).  If it's impossible to bring him inside, you may want to consider building a little mesh wire box around the cage, or hot-gluing mesh to sides of the cage (this is a good sort, the thicker the metal the less chance of injuring things or being easily broken/chewed through - http://www.amazon.com/Mat-Midwest-308238B-36-Inch-50-Foot/dp/B0009GVN4W ).

What the mouse or other creatures may transmit to your guy depends mostly on the area, and since I'm not familiar with New Zealand, a call to your local vet will give you the best idea about what the potential risks are.  Mites, lice, respiratory diseases, and ringworm are a few universal examples of communicable diseases wild mice can give your pet.  There are also other dangers, such as fighting, chewing through the cage bars, bug pests, or other injury risks that could result in infections.

Hopefully Juarez remains in top notch health, and isn't too bothered by his random visitors, but I would definitely beef up his cage security or bring him inside if possible.  :)  Best of luck!

-Tam