Let children make friends with a good microbe

By Gary Raham
Nature Writer and Illustrator

The '80s and '90s saw a dramatic rise in allergies of various sorts, especially in children. Johnny and Jessica got rashes, asthma, bowel problems and even autoimmune diseases in record numbers.

In 1989, epidemiologist David Strachan noted an inverse relationship between family size and children with hereditary, allergen-related (also called atopic) disorders. He proposed what has come to be called the hygiene hypothesis: A lower exposure to microbes in early childhood might somehow lead to increases in allergen-related illness. The hypothesis is still unproven, but researchers have discovered some interesting things about human-microbe ecology while studying the phenomenon. They offer cautions to those who might be tempted to think practicing poor hygiene is okay.

It's taken for granted that most children will live to adulthood. Prior to the 1930s, however, infant death was nearly 10 times as great. Cholera, typhoid, TB, rheumatic fever, smallpox and other infectious diseases commonly took the lives of young children. Better sanitation, chlorinated water supplies, vaccination practices and antibiotics all greatly improved human survival rates. The term "germs" got confused with microbes in general and people got a bit paranoid about cleanliness.

It's important to make the distinction between good hygiene necessary to avoid infectious diseases and the possible lack of exposure to certain benign organisms that might help our bodies distinguish self from non-self. The newest scientific studies highlight several aspects.

• Some microbes are not only good, they're necessary. In fact, to paraphrase the classic cartoon character, Pogo: "We have met the microbes, and they are us."
• Our immune system protects us from the bad guys, and it needs to be primed by a bit of exposure to foreign microbes.
• We're not as clean as we think we are in modern environments.
• We need to be smart and knowledgeable to protect ourselves against infectious disease, but chill out a bit when it comes to healthy contact with Mother Nature.

Microbe metropolis

Human beings are essentially microbial high-rises. Intestinal bacteria make vitamin K for us. Other species line our entire digestive tracts from mouth to netherlands and help keep out foreign critters that would do us harm.

The very energy produced in our cells comes from cell organelles called mitochondria that appear to be once-free-living bacteria that are now essential parts of all animal cell infrastructure. Microbiologist Lynn Margulis estimates that our bodies are composed of 10 quadrillion animal cells plus 100 quadrillion bacterial cells. We are more microbe than animal.

That said, some microbes definitely cause us bodily harm. Our immune systems help protect against such malefactors.

Immunity challenge

White blood cells called lymphocytes recognize foreign invaders. The lymphocytes called T and B cells encounter foreign proteins on the surface of invading microbes and form matching templates (antibodies) that will recognize and attack the same invader should it appear again. The immune system is most active in young individuals. The hygiene hypothesis speculates that if a child doesn't have the opportunity to encounter enough "foreign" cells when his or her immune system is developing, this may result in allergic reactions later in life.

Scientists have discovered some important clues to either verifying or modifying the hygiene hypothesis, but don't yet fully understand the whys.

• Consistently they have found an inverse relationship between allergic issues, family size and birth order. Having older siblings and sharing a room with another child may prevent hayfever and asthma.
• Living on a farm (not just in a rural setting) seems to provide protection from allergic disorders for children, though not older adults.
• Children with allergies show a consistent difference in the microbes that live in their gut. One researcher said, "The key effect of farm living may be early programming of intestinal microflora." Children might need to get up close and personal at an early age with some of the microbes that have become our biological partners over time. Even infection with some roundworms provides protection against allergies.
• Microbes are not the only factors. Traffic emissions, ozone concentrations, diet, socioeconomic status and obesity all seem to play roles. Also, the increased use of antibiotics, in addition to creating super strains of resistant disease microbes, can sometimes destroy some of the good bacteria when overused. Changing microbial ecology in the gut, for example, has been linked to ulcers and bowel problems.

Degrees of clean

The original hygiene hypothesis implied that our modern, ultra-clean environment may not allow adequate exposure to pathogens, but in many ways cleaning techniques have not improved greatly since the end of the 19th century, so those changes predate the allergy problem. Atopic diseases don't correlate with the amount of cleansers people buy. And while hand-washing and thorough cleaning of toilet handles, door knobs and other surfaces with disinfectants can reduce infectious disease, common food and disease pathogens linger in the modern home. They live happily on damp surfaces, including cleaning rags. Researchers say a key question yet to be adequately addressed is "How big does the critical microbial exposure need to be?"

Scientists agree it would be a mistake to lose our fight against serious infectious disease in a misguided effort to avoid allergic disorders. It's too easy to confuse hygiene with cleanliness and dirt with germs.

Some propose that the hygiene hypothesis should become the "microbial deprivation hypothesis" or even the "old friends hypothesis." We must recognize the intimate and complex relationships we have with a vast network of microbes that call our bodies home and forsake simple answers until more complete answers surrender to scientific scrutiny.