Hair of the Dog

LONDON, April 29 (Reuters) - Having a dog in the house reduces the risk that young children will develop allergies, German researchers said on Tuesday. The finding, based on a six-year study of 9,000 children, lends weight to the theory that growing up with a pet trains the immune system to be less sensitive to potential triggers for allergies like asthma, eczema and hay fever. Just why this should be is unclear but scientists believe youngsters may get beneficial early exposure to germs carried into the house on the animal's fur, which helps their immune systems develop.

I wonder if that would work with rats and plague.