I wonder if they looked at a similar protective effect from cats? The last article I saw on something similar said the researchers had found a protective effect against asthma from both dogs and cats in the home before the kids reached age 1. On an anecdotal basis, I believe it .... The home I grew up in was pretty grubby (my mom had better things to do than clean :), and we had cats inside, but only one dog outside. As an adult, I am not allergic to cats, though I am to dogs, and I have never had asthma. My husband grew up in a spotless home with no pets, and both he and one sister have asthma and allergies to cats -- even though neither of their parents had allergies to anything.
Keep a happy, grubby home with lots of critters in it. Works for me!
Gee, I sound awfully mean -- I'm really not - I will stop and feed animals that are hungry and people have dumped out -- I just don't bring them home anymore.