A Cure for the Allergy Epidemic?
Celyn Brazier
By MOISES VELASQUEZ-MANOFF
Published: November 9, 2013
WILL the cure for allergies come from the cowshed?
Allergies are often seen as an accident. Your immune system
misinterprets a harmless protein like dust or peanuts as a threat, and
when you encounter it, you pay the price with sneezing, wheezing, and in the worst cases, death.
What prompts some immune systems to err like this, while others never
do? Some of the vulnerability is surely genetic. But comparative studies
highlight the importance of environment, beginning, it seems, in the
womb. Microbes are one intriguing protective factor. Certain ones seem
to stimulate a mother’s immune system during pregnancy, preventing allergic disease in children.
By emulating this naturally occurring phenomenon, scientists may one day devise a way to prevent allergies.
This task, though still in its infancy, has some urgency. Depending on
the study and population, the prevalence of allergic disease and asthma increased between two- and threefold in the late 20th century, a mysterious trend often called the “allergy epidemic.”
These days, one in five American children have a respiratory allergy like hay fever, and nearly one in 10 have asthma.
Nine people die daily from asthma attacks. While the increase in
respiratory allergies shows some signs of leveling off, the prevalence
of food and skin allergies continues to rise. Five percent of children
are allergic to peanuts, milk and other foods, half again as many as 15
years ago. And each new generation seems to have more severe,
potentially life-threatening allergic reactions than the last.
Some time ago, I visited a place where seemingly protective microbes
occurred spontaneously. It wasn’t a spotless laboratory in some
university somewhere. It was a manure-spattered cowshed in Indiana’s
Amish country.
My guide was Mark Holbreich, an allergist in Indianapolis. He’d recently
discovered that the Amish people who lived in the northern part of the
state were remarkably free of allergies and asthma.
About half of Americans have evidence of allergic sensitization, which
increases the risk of allergic disease. But judging from skin-prick
tests, just 7.2 percent of the 138 Amish children who Dr. Holbreich
tested were sensitized to tree pollens and other allergens. That yawning
difference positions the Indiana Amish among the least allergic
populations ever described in the developed world.
This invulnerability isn’t likely to be genetic. The Amish originally
came to the United States from the German-speaking part of Switzerland,
and these days Swiss children, a genetically similar population, are
about as allergic as Americans.
Ninety-two percent of the Amish children Dr. Holbreich tested either
lived on farms or visited one frequently. Farming, Dr. Holbreich thinks,
is the Amish secret. This idea has some history. Since the late 1990s,
European scientists have investigated what they call the “farm effect.”
The working hypothesis is that innocuous cowshed microbes, plant
material and raw milk protect farming children by favorably stimulating
their immune systems throughout life, particularly early on. That spring
morning, Dr. Holbreich gave me a tour of the bonanza of immune stimuli
under consideration.
We found our hosts, Andrew Mast and his wife, Laura, hard at work milking cows in the predawn chill.
Dr. Holbreich, slight and bespectacled, peppered them with questions. At
what age did Mr. Mast begin working in the cowshed? “My first memory is
of milking,” he said, at about the age of 5. What about his children,
two straw-haired girls, then ages 2 and 3; did they spend time in the
cowshed? The elder girl came to the barn at 3 months of age, he said.
“People learn to walk in here.” Do expectant mothers work in the barn?
“Yes,” Laura said. “We work.”
Dr. Holbreich had made his point: whatever forces were acting here, they
were chronic, and they began before birth. As the sun rose, Dr.
Holbreich and I sniffed the damp, fermented feed (slightly malty);
shoveled fresh cow manure (“Liquid gold,” Dr. Holbreich said only
half-jokingly, “the best medicine you could think of”); and marveled at
the detritus floating in the air. Extrapolating from previous research,
with each breath we were inhaling perhaps 1,000 times more microbes than
usual. By breakfast time, grime had collected under our nails, hay
clung to our clothes, and muck to our boots. “There’s got to be
bacteria, mold and plant material,” Dr. Holbreich said. “You do this
every day for 30 years, 365 days a year, you can see there are so many
exposures.”
The challenge of identifying the important exposures — and getting them
into a bottle — is a pressing one. In parts of the developing world,
where allergic disease was once considered rare, scientists have noted
an uptick, especially in urban areas. China offers a dramatic case in
point. A 2009 study
found a more than threefold difference in allergic sensitization (as
judged by skin-prick tests) between schoolchildren in rural areas around
Beijing and children in the city proper. Doctor-diagnosed asthma
differed sixfold. Maybe not coincidentally, 40 percent of the rural
children had lived on farms their whole lives.
Immigrants from the developing world to the developed tend to be less allergic than average.
But the longer they reside in their adopted countries, the more
allergic they become. And their native-born children seem to gain the
vulnerability to asthma, sometimes surpassing it. All of which
highlights a longstanding question in the allergy field. As Dr.
Holbreich puts it, “What is it about westernization that makes people
allergic?”