Background: Farm children suffer less frequently from pollinosis and bronchial asthma, although they are exposed to higher concentrations of airborne allergens. How do farm children differ from children in the general population with respect to immunological sensitization to airborne allergens?
Methods: Since 1983, a continuing seroepidemiological study of allergic reactions of schoolchildren in a rural area was conducted. Each year, all 15 year-old schoolchildren were given a standardized allergy questionnaire and are tested serologically (RAST/CAP-test) for their IgE sensitization towards the four major groups of airborne allergens: timothy grass pollen, birch pollen, house-dust mites, and cat dander. Farm children were compared with children who only occasionally help out on farms and also with those who had no direct contact with agriculture.
Results: From a total of 1307 children, 1287 questionnaires (98.5%) and 1100 (84.2%) of the serological tests could be analysed. Over the 16 years of the study, a statistically significant increase in the incidence and severity of hay fever and asthma was found in the children with no direct contact to agriculture. This was coupled with a significant increase in the sero-prevalence of sensitisation to the major airborne allergens. Among the 133 farm children, the prevalence of hay fever was: any history of hay fever in 2.4%, hay fever within the last year in none. A history of asthma was found in 1.6% of the children. Among children who occasionally worked on or had contact with farms, the prevalences were: any history of hay fever 9.3%, hay fever within the last year 9.3%, asthma 4.4%. Corresponding prevalences in children with no direct contact to farms were 18.3%, 18.6% and 9.1%, respectively. The seroepidemiological tests showed that the farm children not only had an overall lower rate of seroprevalence of antibodies towards the 4 marker allergens, but they also became sensitized to a lesser extent. At increasing cut-off values of the specific IgE titers, the odds ratio of the farm children in comparison to the control children became increasingly significant. This trend was found with all four marker allergens. The paradoxical immune reaction of farm children towards airborne allergens shows two characteristic quantitative features: in spite of high exposure rates, the children became sensitized less often and more weakly than control classmates from the same village. Children who had intermittent contact with farms showed intermediate results with respect to both symptoms and sensitization.
Conclusions: These farm children have thus become adapted towards the allergens to which they are exposed. This immunological form ist similar to results from East Germany and the former USSR, in spite of the fact that lifestyle and exposure to microbes differ greatly. The immunological adaptation can best be interpreted as the result of a greater and continual stimulation of the Th1-immune response towards anthropozoonotic antigens.