the pros and cons of dirt OR trade-offs in hygiene and health

From Melinda Beck in the WSJ...

Infants are enchanting all over the world, as the new movie "Babies" shows. But their standards of hygiene sure vary.

The film captures the first year of life for four diverse babies. In a nomadic family in Namibia, Ponijao drinks from muddy streams, chews on dry bones and uses her many siblings' body parts as toys.

On a small family farm in Mongolia, a rooster struts around little Bayar's bed, a goat drinks from his bathwater and livestock serve as babysitters.

By contrast, Mari, growing up in high-rise, high-tech Tokyo, and Hattie, whose doting parents live a "green" lifestyle in San Francisco, both have modern conveniences and sanitation.

Statistically, Mari and Hattie are healthier. Some 42 out of 1,000 children in Namibia, and 41 out of 1,000 in Mongolia die before their 5th birthday; compared with only 8 in 1,000 in the U.S. and only 4 in Japan.

Yet the upscale urban infants are at higher risk for some health problems—including allergies, asthma and autoimmune diseases like Type 1 diabetes, multiple sclerosis and inflammatory bowel disease—than the babies in the rural developing world.

While the film makes no mention of hygiene in any of the countries, its images evoke an intriguing medical controversy: Are we too clean, with our preoccupation for hand-sanitizers, disinfectants and anti-microbial products? Now, there's research that suggests there may be a way to get the best of both worlds.

"We seem to be healthier, but we have traded one problem for another problem," says Joel Weinstock, chief of gastroenterology/heptology at Tufts Medical Center in Boston. Using the premise that exposure to a certain amount of dirt and germs carried by livestock may help the body build up resistance to disease, Dr. Weinstock is one of the lead researchers behind clinical trials using pig whipworm eggs to treat peanut allergies, MS and other autoimmune diseases.

According to the "hygiene hypothesis," first proposed in 1989, exposure to a variety of bacteria, viruses and parasitic worms early in life helps prime a child's immune system, much like sensory experiences program his brain. Without such early instruction, the immune system may go haywire and overreact with allergies to foods, pollen and pet dander or turn on the body's own tissue, setting off autoimmune disorders....

Allergies and autoimmune diseases were virtually unknown in the U.S. before the turn of the last century, but they began to emerge as modern sanitation, decontaminated water, food refrigeration and antibiotics became more widespread....

Exposure to a variety of bacteria, viruses and other microorganisms may prime the immune system and protect against certain diseases.

• Children who grow up on farms have low rates of allergies and asthma.
• Having one of more older siblings also protects against hay fever, asthma, multiple sclerosis and Type 1 diabetes.
• Autoimmune diseases are rare in rural Africa and Asia, but rise sharply when immigrants from those countries come to the developed world.
• Infants who attend day care during the first six months of life have a lower incidence of eczema and asthma.
• Rates of asthma are higher in West Germany than East Germany, even though air pollution is worse in the East.
• Type 1 diabetes is six times as prevalent in Finland as it is in neighboring Russia, although genetic backgrounds are similar.

Source: Clinical & Experimental Immunology