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REPEAT. Asthma, the most prevalent chronic childhood disease, affects more than 278 million people worldwide. Environmental factors are implicated in the recent and dramatic rise in asthma cases observed in westernized countries. Growing up on farms has been linked to a significantly lower prevalence of childhood asthma, and, in a report published by the New England Journal of Medicine this week, the U of A's Donata Vercelli and her colleagues report that a key component of the farm environment is the high level of microbes present in house dust on certain farms. By comparing the environments of Amish and Hutterite farm children, who have similar genetic backgrounds and lifestyles but live on different types of farms and have different incidents of asthma, they discovered that the traditional Amish farms, where livestock is kept in barns close to the house, provide sustained exposure to microbes that stimulate the immune system in ways that decrease the susceptibility to asthma. Amish farm dust also protects experimental mice from asthma-like symptoms. The results reported this week are exciting in that they lay the groundwork for the identification of protective environmental products and the development of effective strategies for preventing asthma. In this episode: Donata Vercelli, Ph.D. and Professor of Cellular and Molecular Medicine at the University of Arizona; Leslie Tolbert, Ph.D Regents' Professor in the University of Arizona's Department of Neuroscience