But it is present and can become air-borne from the urine or feces of the contaminated rat. Deer mice as a species lives further from man than field mice, which is one small plus in this whole mess. The paper recommends, if any of your beasts brings home a trophy, that you handle it only from afar with a shovel or something. Of course, related articles point out that mice borne diseases similar to hantavirus may be much more widely contracted than we think. So maybe even grey mice aren't that harmless.
Rodents seem to steer clear of grass and alfalfa hays.