I think long term exposure to some pathogens can help with immunity. Kind of works like a vaccine. Antibodies are produced, etc. This clearly doesn't work for lots of bacterial or viral pathogens though.I imagine that infection still is the most common cause of death in under-developed countries. Most deaths from E. Coli from cows comes from a toxin produced by the bacteria, not the direct effects of bacterial growth.
However, it is becoming increasingly clear to allergy and immunology specialists that we are probably overprotecting our children which in turn produces adults who react to everything. Cats are one example. For years cats were, and still remain, the absolute taboo for allergists. Everyone with allergies must get rid of the cat. Cats should never be around babies. Recent studies, however, show that babies born into a family with an indoor cat are less likely to suffer from cat allergies down the road. It has long been felt that 'farm kids' have fewer allergy problems than city or suburban kids. A recent study took this further and looked at three groups: 1) Farm kids that actually get out and do the work, get around the animals, work in the barn etc., 2) Farm kids that live on a farm but do not actually do any farm type stuff and 3) city/suburban kids.
Well, the farm kids that got their hands dirty had fewer allergies than the other farm kids, who had about the same rate of allergies as suburban kids.
This links the idea of the benefits of early exposure to the 'world'. And the world is made of dirt and dust and grass and all that.
This is not just a matter of who has runny noses or not. Allergies contribute to asthma (which can be life threatening), ear infections, sinus infections, etc. So a population with fewer allergies may be significanltly healthier than an allergy prone population.
