When Fido drags his saliva-drenched tongue across your face, man's best friend may be doing you a microbial favor as well as showing affection.
People are being recruited for a study of whether living with a canine improves the human microbiome. The study is led by University of Arizona researchers along with other universities, including UC San Diego.
"We essentially want to find out, is a dog acting like yogurt in having a probiotic effect?" said Kim Kelly, one of the study leaders, in a press release. Kelly is also a principal research specialist at the University of Arizona in the Department of Psychiatry and program coordinator for the Human-Animal Interaction Research Initiative.
The notion makes many dog owners squeamish, much as they love their canine companions. But bacteria from an even more disquieting source have been recruited for microbiome therapy.
Rob Knight, an internationally known expert on the human microbiome, is leading UC San Diego's part of the study. A newcomer to UCSD, Knight's appointment was announced in January.
"The idea of combining animal, human and environmental health, and seeing the whole picture through the lens of the microbes that we share, is an increasing direction for research," Knight said in a Wednesday interview. There's a growing amount of evidence that dog ownership helps people, he said. Children in dog-owning families have lower rates of asthma and allergies.
Multiple lines of evidence suggest that dog microbiota causes this beneficial effect, said Charles Raison, the study's principal investigator, on Tuesday. One of the paradoxes of modern times is that despite the era's unprecedented cleanliness, allergies and inflammatory diseases have increased.
The lack of bacteria, most of which are harmless and some beneficial, may be to blame under what's called the "Old Friends" hypothesis.
The idea is that humans evolved with bacteria, and grew accustomed to their presence, said Raison, a professor of psychiatry in the university's College of Medicine.
"These bacteria that we call the old friends became teachers of tolerance for the immune system," Raison said. "They took over the job of training the immune system not to react to things that are irrelevant, like pollen."
"There's epidemiological work showing that kids raised with dogs don't tend to get allergies and asthma," he said, citing the studies Knight alluded to. "So we think that dogs have anti-inflammatory effects, based on effects in kids. and increasingly we think now that maybe it's because of sharing the microbiota. There are data that families that have dogs share as much of their microbiota with the dogs as they do with each other."
Another piece of evidence is that when the microbiome of people over 65 gets bad, they're much more likely to become frail, get sick and die, Raison said.
"The data suggest dogs can change people's microbiota," he said.
Some of the benefits of living with dogs are doubtless psychological, Raison said. Measuring changes in microbiota will help distinguish the psychological effect from the microbial.
UCSD researchers are no strangers to microbiota, human or canine. A 2012 team including UCSD participation studied the canine oral microbiome. From the other end, UCSD also hosted research into the canine fecal metagenome.
While the human cargo of microbes has been studied for many years, its relationship with dog microbes is a more recent focus. A study in the April 16 issue of eLife found that family members living together share microbes with each other, and with their dogs.
"Dog ownership significantly increased the shared skin microbiota in cohabiting adults, and dog-owning adults shared more ‘skin’ microbiota with their own dogs than with other dogs," the eLife study stated.
Dogs have co-evolved with people for tens of thousands of years. Scientists generally agree that this symbiosis was important in human civilization. Dogs evolved from wolves, acquiring a predisposition for human companionship and a recognition of people as the top dog (most of the time).
The common telling of the story has it that humans domesticated dogs. But some maintain the converse -- dogs actually domesticated people.
Source: UT SanDiego
Photo Source: Jamie Scott Lytle
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