Attend a big infectious diseases meeting and it’s easy to start thinking, at least for a few days, that infections lie at the root of most human disorders. In a colder light, that may seem a lot less likely, but at the annual meeting of the Infectious Diseases Society of America in Boston last month, Dr. Julie Parsonnet, a professor of medicine and an epidemiologist at Stanford, spun a pretty infection-centric narrative on the links between pathogens and chronic diseases.
“I’m convinced we’re going to find a huge amount of information" about chronic diseases and infections, she concluded in a featured talk at the meeting. She speculated on and offered some evidence for a role of microbes in a variety of chronic conditions, like cancers, vascular disease, cystic fibrosis, and obesity. It’s an understandable view from a researcher who, nearly 2 decades ago, came to medical prominence by leading a group of researchers who found good evidence that gastric infection by Helicobacter pylori linked to the development of gastric mucosa-associated lymphoid tissue (MALT) lymphomas. She also noted that the pathogen-chronic pathology idea didn’t start with her, citing a 2000 book, Plague Time by Paul W. Ewald, that posited the same notion.
Wikimedia Commons/Ed Uthman/Creative Commons License
Helicobacter pylori in a gastric foveloa.
Last month, she focused on a possible role for H. Pylori and other gut flora in obesity. “H. pylori seems to affect appetite, and what you want to eat,” she noted, while “other chronic infections, like Giardia, can affect what’s absorbed” through the GI tract. “Gut flora can affect what you feel like eating, what gets absorbed, and basal metabolic rate,” she noted. “Weight is very complicated, but I guarantee that infection plays a strong role in what happens with it.”
Perhaps, or her theory could be dismissed as speculation. Except the next day at the meeting researchers from Columbia University in New York, who had nothing to do with Dr. Parsonnet, reported suggestive evidence linking past exposure to H. pylori and new-onset diabetes. Data from a prospective study of 790 Latino Americans more than 60 years old and living in the Sacramento area showed people with positive serology for H. pylori had a greater than two-fold risk for later developing diabetes. In a multivariate analysis that controlled for a list of potential confounders, study participants who were seropositive for H. pylori at baseline had a statistically significant, 2.7-fold increased rate of incident diabetes during more than 8 years of follow-up, reported Dr. Christie Y. Jeon, a researcher at Columbia.
The link between H. pylori seropositivity and diabetes did not seem related to inflammation or insulin resistance. Her best guess at what links the two was that gut microbiota cause changes in nutrient metabolism, energy harvesting, or gene expression, she said. But the association she reported provides only a hint, if for no other reason that the H. pylori marker Dr. Jeon relied on was seropositivity, a sign of exposure sometime during the subject’s lifespan, without evidence for a recent, active infection.
Just a hint, but perhaps enough to make a link between infection and chronic disease sound more plausible.
---Mitchel Zoler (on Twitter @mitchelzoler)