Hi,

Could it be worth trying to completely disinfect the cages you are using for the rats rather than the mild cleaners you are currently using?

Just in case it was something that came in earlier and has managed to hang around?

Is it possible it is something that is present in the mouse population but doesn't really cause them any problems but quickly affects the rats?

The quarantine idea might help you find that out if you disinfect the cages amd move them to another area. If that rats are fine there but die when introduced to the same area as the mice then you know that is probably the issue.


dr del