There is a test that can be used to see if the mouse carries hantavirus. I believe it's called a PCR test which uses blood, saliva, urine or feces. Unlike rabies which calls for the animal to be euthanized in order to check brain tissue, this test can be done without sacrificing the mouse.
Mice can carry the virus and not show symptoms. Typically people develop flu-like symptoms within 1 - 6 weeks after exposure. I've also raised plenty of deer mice (part of my wildlife rehab job) and never had a problem with it. I'm careful with the bedding and wash my hands regularly. I don't know the percentage of baby mice that carry the virus. In the adult population it's still a fairly small percentage.
You can check with a vet, see if they're set up to do the test or you may have to check with the health dept. They may not be so keen on doing it though just so you can keep the mouse as a pet. Don't know till you ask. And one last thing, I'm not sure of the laws in your state about keeping a wild animal in your care. There are restrictions against that but it depends on species. Usually the Fish and Wildlife division has a spot on their site listing which species are protected and the laws about permanent captivity.
Thank you. That was the most informative answer I have gotten anywhere. I spoke with two exotic animal vets who also do wildlife rehab but neither was aware of a test. One is checking with the state lab. I will check with the health dept. Baxter is so adorable. Kept me up all night running on his wheel. Thanks again,
Happy I was able to help. I'm rather fond of mice and rats myself. But I tend to get them from friends or the pet store. They make great companions.