It's official - the medical community has accepted that a key element in preventing allergies and asthma is early childhood exposure to allergens - whether peanuts, dust, or pets. Instead of avoiding the allergens (which was the medical advice for decades) - getting early exposure to them is key to preventing allergies. Apparently growing up on a farm is best (with exposure to farm dirt and dust), especially a dairy farm with animals and raw milk (a number of studies have found that unprocessed raw milk and its microbes also helps health). But if one doesn't live on a farm, then having furry pets in early childhood is also beneficial in reducing the incidence of allergies. The following study shows that microbes are involved - pet microbes were found in the guts of many of those children who did not develop early allergies! From Medscape:
In a small, preliminary study, infants in households with furry pets were found to share some of the animals' gut bacteria - possibly explaining why early animal exposure may protect against some allergies, researchers say. The infants' mothers had a history of allergy, so the babies were at increased risk. It was once thought that pets might be a trigger for allergies in such children, the authors pointed out online September 3 in the Journal of Allergy and Clinical Immunology.
"Earlier it was thought that exposure to pets early in childhood was a risk factor for developing allergic disease," coauthor Dr. Merja Nermes, of the University of Turku in Finland, told Reuters Health by email. "Later epidemiologic studies have given contradictory results and even suggested that early exposure to pets may be protective against allergies, though the mechanisms of this protective effect have remained elusive."Adding pet microbes to the infant intestinal biome may strengthen the immune system, she said.
From participants in an ongoing probiotic study of pregnant women with a history of allergies, Nermes and her colleagues selected 51 infants of families with furry pets (dogs, cats or rabbits) in the home and 64 infants with no pet in the home. Fecal samples collected from diapers when the babies were one month of age were tested for the DNA of two types of Bifidobacteria that are found specifically in animal guts: B. thermophilum and B. pseudolongum. One-third of infants from the pet-exposed group had animal-specific bifidobacteria in their fecal samples, compared to 14% of controls. It's not clear where the infants without furry pets at home acquired the bacteria, the authors wrote.
When the babies were six months old they had skin prick tests to assess allergies to cow's milk, egg white, flours, cod, soybeans, birch, grasses, cat, dog, potato, banana, and other allergens. Nineteen infants had reactions to at least one of the allergens tested. None of these infants had B. thermophilum in their fecal samples.
Past research has linked growing up on a farm or exposure to dog dander indoors with protection against airway allergens, the study team wrote. Other studies have found increased "richness and diversity" in the gut microbes of kids exposed to household pets."When infants and furry pets live in close contact in the same household, transfer of microbiota between pets and infants occurs," Nermes said. "Human-specific Bifidobacteria have beneficial health effects, and animal-specific strains may also be beneficial, she said. It is still unclear, however, if exposure to these bacteria protects against allergies later in life, she said.
Other researchers point out that the dirty farm dust may trigger low level inflammation in the lungs of young children which is somehow protective (and prevents allergies and asthma from happening). Go to the link for more details on the study. From Science Magazine: Dirty farm air may ward off asthma in children
For researchers trying to untangle the roots of the current epidemic of asthma, one observation is especially intriguing: Children who grow up on dairy farms are much less likely than the average child to develop the respiratory disease. Now, a European team studying mice has homed in on a possible explanation: Bits of bacteria found in farm dust trigger an inflammatory response in the animals’ lungs that later protects them from asthma. An enzyme involved in this defense is sometimes disabled in people with asthma, suggesting that treatments inspired by this molecule could ward off the condition in people.
The study, published on page 1106, offers new support for the so-called hygiene hypothesis, a 26-year-old idea that posits that our modern zeal for cleanliness and widespread use of antibiotics have purged the environment of microorganisms that once taught a child’s developing immune system not to overreact to foreign substances.... But others caution that the finding is probably far from the only explanation for why early exposure to microbes can make kids less allergy-prone.
About 20 studies in Europe and elsewhere have found that children raised on farms have relatively low rates of allergies and asthma. Some researchers suspect a key reason is that the kids breathe in air full of molecules from the cell wall of certain bacteria, called lipopolysaccharides for their fat-sugar structure. Also known as endotoxins, these fragments—from dying bacteria in cow manure and fodder—cause a temporary low state of inflammation in the lungs that somehow dampens the immune system’s response to allergens, the thinking goes.
Others who study the hygiene hypothesis caution that the newly uncovered mechanism does not entirely explain the protective effect of dairy farm life. Drinking unprocessed milk also seems to ward off asthma in kids, points out Gary Huffnagle of the University of Michigan, Ann Arbor—and that effect is unlikely to involve the lung epithelium. What’s more, endotoxin levels are not that much higher on farms than in cities, suggesting “it’s too simple an answer,” says asthma genetics researcher William Cookson of Imperial College London, who thinks changes in living microbial communities in the lungs and gut may be just as important.