August 10th, 2011
04:23 PM ET
When was the last time you, your children or anyone you know was treated for worms? If you’re under the age of 40, your likely answer is “Never!”
This is no accident. As a society we have become cleaner and cleaner, more and more antiseptic, more and more hygienic over the last half century.
As we’ve done so, a huge array of microorganisms - worms among them - have silently, and with no fanfare, vanished from our daily environments. Some worms have even gone extinct inside our pets.
Industrialized countries such as the United States began making serious efforts to sanitize their environments in the 19th century. These public health efforts have done more to reduce disease and enhance longevity than any medical intervention before or since.
But scientific evidence increasingly suggests that the victories achieved by cleanliness have come at a significant health cost that is only now beginning to be fully appreciated.
Earlier than 100 years ago, almost everyone died from infection, most often in childhood. That doesn’t happen anymore in the developed world. Conversely, more than 100 years ago (more or less) many autoimmune and inflammatory conditions that are very common today (rheumatoid arthritis, multiple sclerosis, type 1 diabetes, hay fever, asthma) were so rare as to be essentially non-existent. It turns out that these two facts are intimately related.
By cleaning up the environments in which we live, we have eradicated an incredible array of dangerous pathogens that used to cause disease by passing from person to person with relative impunity. But without even realizing we were doing it, we’ve also removed an even larger host of benign bugs (mostly bacteria) and relatively benign nasties (mostly worms) with which we were once in near constant contact from birth to death.
It is increasingly clear that these ubiquitous microorganisms co-evolved with humans for so long that our immune systems came to depend on them to learn what should be properly attacked and what could be ignored.
Most of us seem to do OK without the presence of these microbial teachers, but people with various genetic risk factors appear to be far more likely to develop autoimmune, allergic or asthmatic in the absence of our “old friends,” as these protective microbes have been called.
Evidence for this idea has been piling up for decades, and is far too vast for me to do more than touch upon here. First came studies showing that children raised around livestock on farms almost never get allergies or asthma, followed by other studies showing that rates of autoimmune and allergic disorders skyrocket when countries transition from third world to first world living conditions.
Finally, recent work has shown that various types of “old friend” microorganisms are able to suppress the types of inflammatory activity that promote so many modern immune-based maladies.
Back to the worms. If loss of contact with “old friend” microorganisms increases the risk for developing autoimmune diseases and asthma/allergy, is it possible that reintroducing these organisms might help treat these diseases? Increasingly the answer appears to be yes.
Recent studies suggest that treating people with worms may improve multiple sclerosis, type 1 diabetes and inflammatory bowel disease. And another “old friend” species—this time a harmless bacterium related to the tuberculosis bug—has been shown to enhance survival when combined with chemotherapy for the treatment of a type of cancer known as adenocarcinoma of the lung.
Remarkably, this bacterium, known as M. vaccae, has also been shown to reduce depression and anxiety in patients with cancer, suggesting that the “old friends” might hold promise for the treatment of psychiatric conditions.
This isn’t as outlandish an idea as it sounds. Like allergic and autoimmune disorders, major depression appears to have dramatically increased in prevalence in the modern world. Moreover, all the other immune-based diseases that become common in societies that modernize are also strongly associated with depression.
For example, asthma in childhood strongly predicts the development of depression in adulthood. Finally, as a group, people with depression, even when they are otherwise medically healthy, show many of the same types of inflammatory abnormalities that characterize allergic and autoimmune diseases.
Treating depression with worms or bacteria is not ready for prime time, but a clear implication of recent scientific findings is that we do our children no favors when we insist they live in a hyper-sterilized world. Playing in the dirt, and a few kisses from dogs now and then, may literally be good for both their physical and mental health.
For a more detailed discussion of ideas in this blog, see my article "Inflammation, Sanitation and Consternation: Loss of Contact with Co-Evolved, Tolerogenic Micro-Organisms and the Pathophysiology and Treatment of Major Depression" in the December 2010 edition of Archives of General Psychiatry.
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