Allergies seem nearly impossible to avoid — unless you're Amish

Washington Post

6 days ago

Whether triggered by pollen, pet dander or peanuts, allergies in this day and age seem nearly impossible to avoid. But one group appears virtually immune, a mystery to experts who study allergies.
Despite the increasing rate of allergic diseases, both in industrialized and in developing countries, the Amish remain exceptionally — and bafflingly — resistant. Only 7 percent of Amish children had a positive response to one or more common allergens in a skin prick test, compared with more than half of the general U.S. population. Even children from other traditional farming families, who still have lower rates of allergic disease than nonfarm children, are more allergic than the Amish.
In fact, one Amish community living in northern Indiana is considered one of the least allergic populations ever measured in the developed world.
'Generally, across the country, about 8 to 10 percent of kids have asthma. In the Amish kids, it's probably 1 to 2 percent,' said Carole Ober, chair of human genetics at the University of Chicago. 'A few of them do have allergies, but at much, much lower rates compared to the general population.'
Now, Ober and other researchers are trying to discover what makes Amish and other traditional farming communities unique, in the hopes of developing a protective treatment that could be given to young children. For instance, a probiotic or essential oil that contains substances found in farm dust, such as microbes and the molecules they produce, could stimulate children's immune systems in a way that prevents allergic disease.
'Certain kinds of farming practices, particularly the very traditional ones, have this extraordinary protective effect in the sense that, in these communities, asthma and allergies are virtually unknown,' said Donata Vercelli, a professor of cellular and molecular medicine at the University of Arizona. 'The studies that have been done in these farming populations are critical because they tell us that protection is an attainable goal.'
The Amish are members of a Christian group who practice traditional farming — many live on single-family dairy farms — and use horses for fieldwork and transportation. As of 2024, around 395,000 Amish live in the United States, concentrated mostly in Pennsylvania, Ohio and Indiana.
Over the past century, the incidence of allergic diseases — including hay fever (allergic rhinitis), asthma, food allergies and eczema — has increased dramatically. Hay fever, or an allergic reaction to tree, grass and weed pollens, emerged as the first recognized allergic disease in the early 1800s, climbing to epidemic levels in Europe and North America by 1900.
The 1960s saw a sharp increase in the prevalence of pediatric asthma, a condition in which the airways tighten when breathing in an allergen. From the 1990s onward, there has been an upswing in the developed world in food allergies, including cow's milk, peanut and egg allergies.
Urbanization, air pollution, dietary changes and an indoor lifestyle are often cited as possible factors.
The 'hygiene hypothesis' — first proposed in a 1989 study by American immunologist David Strachan — suggests that early childhood exposure to microbes protects against allergic diseases by contributing to the development of a healthy immune system.
The study found that hay fever and eczema were less common among children born into larger families. Strachan wondered whether unhygienic contact with older siblings served as a protection against allergies.
Subsequent findings have given support to the hygiene hypothesis, such as that children who grow up with more household pets are less likely to develop asthma, hay fever or eczema. Perhaps even more beneficial than having older siblings or pets, however, is growing up on a farm. (More than 150 years ago, hay fever was known as an 'aristocratic disease,' almost wholly confined to the upper classes of society. Farmers appeared relatively immune.)
This 'farm effect' has been confirmed by studies on agricultural populations around the world, including in the United States, Europe, Asia and South America. But even among farming communities, the most pronounced effect appears to be in the Amish. In a study of 60 schoolchildren by Ober, Vercelli and their colleagues, the prevalence of asthma was four times lower in the Amish as compared with the Hutterites, another U.S. farming community with a similar genetic ancestry and lifestyle.
The prevalence of allergic sensitization — the development of antibodies to allergens and the first step to developing an allergy — was six times higher in the Hutterites. The researchers first ruled out a genetic cause; in fact, an analysis showed that the Amish and Hutterite children were remarkably similar in their ancestral roots. Instead, the main difference between these two populations seemed to be the amount of exposure as young children to farm animals or barns.
'The Hutterite kids and pregnant moms don't go into the animal barns. Kids aren't really exposed to the animal barns until they're like 12 or so, when they start learning how to do the work on the farm,' Ober said. 'The Amish kids are in and out of the cow barns all day long from an early age.'
When analyzing samples of Amish and Hutterite house dust, they found a microbial load almost seven times higher in Amish homes. Later experiments showed that the airways of mice that inhaled Amish dust had dramatically reduced asthmalike symptoms when exposed to allergens. Mice that inhaled Hutterite dust did not receive the same benefit.
Now, Ober and Vercelli are beginning to identify the protective agents in Amish dust that prevent allergic asthma. In 2023, their analysis of farm dust found proteins that act like delivery trucks, loaded with molecules produced by microbes and plants. When these transport proteins deliver their cargo to the mucus that lines the respiratory tract, it creates a protective environment that regulates airway responses and prevents inflammation.
'We don't really talk about the hygiene hypothesis as much anymore because we now understand that it's not really about how hygienic you're living,' said Kirsi Järvinen-Seppo, director of the Center for Food Allergy at the University of Rochester Medical Center. 'It's more like a microbial hypothesis, since beneficial bacteria that colonize the gut and other mucosal surfaces play a significant role.'
During the first year or two of life, a baby's immune system is rapidly developing and highly malleable by environmental stimuli, such as bacteria. Some experts believe that exposing young children to certain types of beneficial bacteria can engage and shape the growing immune system in a way that reduces the risk of allergic diseases later in life. Farm dust contains a hodgepodge of bacteria shed from livestock and animal feed that isn't harmful enough to cause illness, but does effectively train the immune system to become less responsive to allergens later in life.
In 2021, Järvinen-Seppo and her colleagues compared the gut microbiomes of 65 Old Order Mennonite infants from a rural community in New York with 39 urban/suburban infants from nearby Rochester. Like the Amish, the Old Order Mennonites follow a traditional agrarian lifestyle. Almost three-fourths of Mennonite infants in the study were colonized with B. infantis, a bacterium associated with lower rates of allergic diseases, in contrast to 21 percent of Rochester infants.
'The colonization rate is very low in the United States and other Western countries, compared to very high rates in Mennonite communities, similar to some developing countries,' Järvinen-Seppo said. 'This mirrors the rates of autoimmune and allergic diseases.' These clues about the origin of the farm effect represent a step toward the prevention of allergic diseases, Järvinen-Seppo says.
Whatever form the treatment takes, the impact on prevention of allergic diseases, which affect millions of people worldwide and reduce quality of life, could be enormous, experts say.
'I don't know that we can give every family a cow. … But we are learning from these time-honored and very stable environments what type of substances and exposures are needed,' Vercelli said. 'Once we know that, I don't think there will be any impediment to creating protective strategies along these lines.'