Blaser argues that today's medical practices—particularly the overuse of antibiotics and Cesarean sections—are destroying the "microbiome,"the set of living microorganisms, including bacteria, within us that fosters human health.
Why should we care?
It turns out that even the microbes that have a bad name, such as H. Pylori (which is associated with ulcers and stomach cancer), may have benefits that were overlooked. Blaser argues that the disappearance of these critical organisms has contributed to the increase in "modern plagues" that are now threatening the public's health, including obesity, asthma, allergies, diabetes, and certain cancers. His central argument is that many of the microbes, like H. Pylori, represent double-edged swords. H. Pylori, to the surprise of many scientists, has been found to be protective against gastrointestinal reflux disease (GERD), esophageal cancer, allergies, hay fever, and irritable bowel diseases. Its presence is also associated with a lower susceptibility to obesity, diabetes, and future infections. These discoveries cast the decades-long efforts to eradicate this and other "friendly" bacteria in a new light.
Building off more than 30 years of scholarship and clinical experience in the role of bacteria in human disease, Blaser's theories have challenged the prevailing wisdom in the medical community. His career— he is currently director of the Human Microbiome Project at New York University, the former president of the Infectious Diseases Society of America, and an advisor to the National Institutes of Health,— has been characterized by a willingness to upset the apple cart.
Blaser's theory, which he explained in an interview this week with WHYY's Terry Gross, is that the destruction of microbes—especially the notorious H. Pylori—through antibiotic use and other modern practices has contributed to the increase of diseases. The good bugs had been living collaboratively and competitively with our other cells for years, facilitating our metabolisms, immune responses, and other processes. Modern sanitation—one of public health's greatest successes—has made transmission of H. Pylori from person to person much less likely, since the microbe's main reservoir is the human stomach and transmission is generally limited to exposure to airborne microbial spores from vomit or via the fecal-oral route (contaminated food or water). In addition, with the increasing use of broad-spectrum antibiotics that kill friendly and foe bacteria alike, Blaser writes, the population of microorganisms has been slowly shrinking. And the trend towards smaller families means that young children are less likely to be exposed from their older siblings, who used to represent a source of transmission when large families lived in closer quarters.
Blaser argues that these factors combined have led to the disappearance of H. Pylori in each successive generation. He and his colleagues have found inverse relationships between the presence of the microbe and the modern plagues; individuals who lack the microbes at birth are less likely to acquire them later, and their absence is associated with higher rates of the aforementioned diseases.
By 2010, 258 million courses of antibiotics a year were prescribed to people in the United States. The highest rate was for children under age two, and most antibiotics prescribed for kids are for upper respiratory infections— many caused by viruses that will not respond to them. Meanwhile, the broad-spectrum antibiotics destroy all the bacteria in their path, including the good microbes that we need to facilitate healthy immune responses and metabolic processes throughout life. We are exposed to still more antibiotics through animal products due to their rampant use in low doses in industrialized agriculture. As Blaser points out, it is not surprising that the antibiotics—and hormones—that are used to promote weight gain in animals we eat have been linked to a rise in human obesity and earlier puberty. And the recent increase in C-sections (up 50% between 1996 and 2011) means that many infants are no longer exposed to the natural microbes present in their mothers’ vaginas, since they do not pass through the birth canal. Blaser argues that the combination of missing out on this exposure and being exposed to broad-spectrum antibiotics at a young age has profoundly disrupted our microbiomes, contributing to the rise in the modern plagues.
The author's conversational writing style makes the book appealing for a layperson who might not share Blaser's scientific expertise. He intersperses personal anecdotes—like his own harrowing bout of paratyphoid caused by salmonella-tainted watermelon in Mumbai—with clear descriptions of "hard science." Not only are these stories interesting, but they convey his recognition of the life-saving power of antibiotics, providing a more balanced tone to his argument about the dangers of antibiotic overuse. There are also long passages that describe the methodology of his studies; these allow the reader to understand how Blaser arrived at his conclusions. Each description of a laboratory process is followed by a succinct explanation of why the experiment matters: how it links back to the original hypothesis and what questions it raises for future studies.
The resounding message of Missing Microbes is that every "solution"—be it in medicine, public health, or policy—has unintended consequences. While nationalorganizations like the Centers for Disease Control and Prevention generate awareness about antibiotic resistance, there is very little—if any—discussion of the destruction of the microbiome. Blaser warns that the time to act is now, before our elusive "friendly" bacteria are gone forever. In his final chapter, he offers solutions, including resisting use of antibiotics for coughs and colds unless it is absolutely necessary and reducing use of antibacterial hand sanitizers when soap and water would suffice.
All told, Missing Microbes presents a surprisingly clear perspective on a complex problem. The role of microorganisms, it turns out, is more complicated than experts once thought. Like any "solution," the eradication of H. Pylori and the other so-called bad guys inside us may have a biological cost that is worth exploring.