Preventive Medicine Column

Dr. David L. Katz

We have long known that bacteria living on and in our bodies outnumber our cells- which themselves sum up to a number that exceeds any hope of real understanding- by 20 to one. And we have increasing evidence of the profound influence of these intimate neighbors on far more than just digestion.

We have also long known that the particular cells of the immune system responsible for inflammation in allergy and asthma, called eosinophils, are the cells on which the body calls to fight parasites.  Other cells preferentially get the call for dealing with viruses (lymphocytes), or pathogenic bacteria (neutrophils).

And we have long seen a pattern in global epidemiology that hints at something profound about our place in nature, and nature’s place in us.  By and large, societies that still have parasites to contend with don’t have allergies or asthma.  Societies, such as ours, burdened by allergy and asthma, have mostly banished our parasites- such as the various worms that would otherwise take up residence in our gastrointestinal tracts.

Such time-honored knowledge is inviting the evolution of new thinking.  Maybe parasites aren’t all bad.

It may be that the inverse association between parasites and asthma is actually about cause and effect.  In the simplest of potential explanations, it may be that when eosinophils are busy doing the job for which they were intended, they don’t have the opportunity to loiter in the lungs and cause trouble.  It may be that when an immune system has real work to do, it doesn’t get all worked up over pollen.  Humans cannot be pollenated; pollen is not a genuine threat.

The plot quickly thickens thereafter.  If immune system idleness leads to pollen-related mischief, it may underlie far more serious pathologies as well.

Autoimmune diseases are diverse and widespread, and in the aggregate account for a huge portion of the disease burden in modern societies, an enormous toll of misery, astronomical costs, and highly prevalent disability.   The category includes conditions ranging from multiple sclerosis, to rheumatoid arthritis, to inflammatory bowel diseases.

There is very little inflammatory bowel disease in parts of the world where bowels accommodate helminthic worms.

There are now some studies indicating a potential therapeutic benefit of introducing such parasites as a treatment for inflammatory bowel disease.  Other studies suggest comparable benefit for diverse autoimmune diseases, such as MS, having nothing obviously to do with the bowel.  And since inflammation underlies the most prevalent chronic diseases of all- heart disease, cancer, and diabetes- a potential link there, too, is well within the bounds of current thinking.

The mechanisms of such benefit remain a topic of conjecture.  Parasites influence the regulation and responses of the immune system; may alter the integrity of the gut lining; and may simply occupy immune cells otherwise at liberty to cause trouble.  It’s all a work in progress, as are the relevant therapeutic options.

For now, the use of probiotic bacteria in capsule form as a therapeutic modality for such conditions as irritable bowel syndrome is increasingly routine.  The use of therapeutic parasites is not yet routine, or even routinely accessible- but movement in that direction no longer looks implausible.

We have much yet to learn about the optimal balance between distancing ourselves from the dangers of predation by such means as antibiotics and hygiene, and accommodating the ecological equilibrium of which we are an indelible part, and to which we are adapted.  On the topic of antibiotics and indelible linkages, a recent study indicates that antibiotics used routinely in livestock leave residues in the meats from which sausages are made.  These, in turn, kill bacteria used intentionally in the making of sausage, and responsible for a fermentation process relied upon to kill other bacteria, such as E. coli and salmonella, which can otherwise hurt, or even kill us.  The law of unintended consequences may never have been more dramatically ratified.

There is abundant and burgeoning cause to respect our place in nature, and nature’s place in us. We are clearly deceiving ourselves to think we can untangle that web of life haphazardly, and not suffer consequences.




Dr. David L. Katz;