Don't clean that mouse cage!

Not suprisingly it seems rats in sewers are healthier than those in labs, giving some support to the hygiene theory. Growing up in the slums, might help your immune system cope better than that of priviliged westerners, explaining the epidemiological spread of things like asthma... "Gritty rats and mice living in sewers and farms seem to have healthier immune systems than their squeaky clean cousins that frolic in cushy antiseptic labs, two studies indicate. The lesson for humans: Clean living may make us sick"