Houseing mice and rats together

Just so no one gets a heart attack, i am not housing rats and mice together(on purpose), and never plan on doing so.

BUT... I had to travel for about 40 minutes with five mice and four rats, and all i had was a huge rat cage that is three levels, so i covered up the hole leading to the second level, stuck my mice in the second level, and my rats in the first. Every thing is going fine and when i get home i go to take the mice to their cage, and i just about died when i lifted up their hide. My largest Berkshire rat was in there with my mice:O The second level was still blocked off, so im guessing some how he snuck up there into their hide right before i closed up the second level while i was picking up what i needed to cover the hole, and for some unknown reason i did not lift up the mouse hide before i left to make sure that didnt happen.

What would the possible outcomes be with houseing these two species together? I am just takeing a guess but i could see them shareing parasites and fighting?

Please do not turn this into a yelling match screaming NO, i know that these are never going to be housed together, i just want to know if anyone has any backround information on it, Cheers,
Matt!;)

I know this is a really old post but I thought I would answer. Rats can and will kill mice. Its called muricide. Mice that can smell rats get stressed and have smaller litters and other such stress related issues. Rats tend to bite through the spinal cord at the base of the head. Here is some reading material http://www.ratbehavior.org/RatsMice.htm

Wow I forgot that I had made this, it was such a long time ago.