Conference Coverage

Farm Living Linked to Low Asthma Prevalence



ORLANDO – Amish farms appear to be havens of peace and contentment, free from the insults of modern life – including, it appears, inhalant allergies and asthma, researchers reported at the annual meeting of the American Academy of Allergy, Asthma, and Immunology.

A study comparing asthma and allergic rhinitis prevalence among Amish children in the United States with those of Swiss children living both on and off farms shows that asthma prevalence among the Amish is low and similar to that of children living on Swiss farms, lending further support to the hygiene hypothesis of allergy and asthma, said Dr. Mark Holbreich of Allergy & Asthma Consultants in Indianapolis.

Only 8 (5%) of 157 in a sample of Amish children had ever received a diagnosis of asthma, and only 1 (0.6%) had ever been diagnosed with hay fever. Swiss farm children had similarly low prevalence levels, with 202 (6.7%) of 3,006 having ever been diagnosed with asthma, and 94 (3.1%) with allergy. In contrast, 1,218 (11.2%) of 10,912 Swiss non–farm dwelling children had been diagnosed with asthma, and 1,259 (11.6%) had a hay fever diagnosis at some point in their lives.

"This study clearly supports the effect of early farm exposures in reducing allergic sensitization," said Dr. Holbreich.

Although the sample of Amish children was too small to determine whether specific factors were protective in farm dwellers both in the United States and Europe, multivariate analyses from other studies suggest that drinking raw, unpasteurized milk, and child and maternal exposure to large animals (especially cows) during pregnancy may confer immune tolerance on the child, Dr. Holbreich said in an interview.

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It pays to grow up around grass; the number of farm-dwelling Amish children who suffer from asthma or allergies is quite low.

The investigators chose for their comparison group Swiss children aged 6-12 years enrolled in the phase I GABRIEL study, which looked at genetic and environmental causes of asthma in Europe. A stratified sample of these children had undergone serum specific immunoglobulin E (IgE) testing to inhalant allergens, including house dust mites (Dermatophagoides pteronyssinus), cat, birch, mixed trees, and grasses. The GABRIEL investigators defined atopy as any positive IgE level of 0.7 kU/L or greater.

Dr. Holbreich and his colleagues distributed to the families of Amish school children a modified GABRIEL questionnaire, and invited consenting children to a skin test session at the school. The children were tested for skin-prick response to D. pteronyssinus, D. farinae, grass mix, tree mix, ragweed, cat, horse, and Alternaria. They considered a skin prick test positive if it induced a 3-mm or greater wheal after subtraction of the negative control.

Although the testing methods were different between the groups (skin-prick testing for the Amish children, and IgE for the Swiss children), the investigators are confident that the prevalence results are valid, Dr. Holbreich said.

Dust mites were the common offenders in causing atopy among the Amish children (5.8%), with sensitivity to mixed grasses occurring in 2.9%. In contrast, 20.1% of Swiss farm dwelling children, and 39.8% of children who did not live on farms had grass sensitivity, with dust mite sensitivity coming in second (9.3% and 16.4%, respectively), and with birch being the third most common allergen (80% and 19.6%, respectively).

Asked in the question-and-response portion of his presentation whether helminth infections might play a role in allergic desensitization of the Amish children, Dr. Holbreich noted that the Amish people "live a very traditional lifestyle, but they see doctors, they get all their immunizations, and they’re cleanly, and I’m not aware of data [showing] that Amish get helminth infections, so I don’t think that is a factor."

The study was supported by the St. Vincent Foundation, AAAAI, and the European Commission. Dr. Holbreich reported having no conflicts of interest.

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