Abstract
Background: A lower allergy and asthma prevalence in farm children has
been described three decades ago in Switzerland. After years of research
into bacterial exposure at farms, the origin of the farm effect is
unknown. It could be still the effect of a sampling bias. As there was
never any effect in large industrial cattle farms with slatted floors,
we now hypothesize that in small farms, where animals are grazing
outdoors, children may be exposed to animals with a higher endoparasite
load. Methods: We re-analyze an earlier epidemiological study by
record-linkage to later agricultural surveys. The Asthma and Allergy
Study in 1989/90 was a cross-sectional study of 1714 ten year old
children in 63 villages covering ten different districts of Upper
Bavaria. The farm effect is defined here as the association of number of
cows per villager on lifetime prevalence of allergic rhinitis prevalence
in the children. Results: The farm effect is restricted to small
villages only. Furthermore, districts with a higher Fasciola infection
rates of cows, show a stronger farm effect than districts with lower
infection rates. Conclusions: Research into parasite effector molecules
is warranted.