August 28, 2002
Exposure to at least two dogs or cats in the first year of life may drastically reduce the risk of allergies, including reactions to molds, grasses and pollen, scientists report in an unusual line of research published today.
The team of Georgia scientists pursuing this seemingly offbeat path
of research say they now have some fairly solid leads on
how animals help ward off allergies, including those known to trigger asthma.
"We started this research almost 14 years ago,
looking at all of the factors that cause allergies," said Dr. Dennis
professor of pediatrics and medicine at the Medical College of Georgia in Atlanta. Ownby and his team report the results of
their investigation in today's Journal of the American Medical Association. In the study, allergies - or the lack of them - were
studied in nearly 500 healthy children born between April 15, 1987, and Aug. 31, 1989.
A key in the research was to pinpoint the
of exposure children had by age 1 to cats and dogs, the most common
pets. Those with exposure to at least two dogs or cats had a 75 percent lower risk of allergies. The study found that just one
pet didn't confer protection.
Ownby theorizes that exposure to the protein
of a certain class of bacteria known as gram-negative explains why
some children have such a dramatically lower risk of serious allergies. Gram-negative bacteria include E. coli and other
organisms that can be found in animal feces.
Pets lick themselves and spread the byproduct
of the bacteria on their fur. Bacterial byproducts are transferred to
pet, kiss or hug the animals, Ownby said.
"We think that something related to the
exposure forces the immune system away from the predisposition to
reactions," Ownby said. Such exposure, he added, also minimizes the effects of other potential allergens, such as molds, pollens
Prior studies in Europe showed that children who grew up on farms
were in the constant presence of animals tended to
have fewer allergies.
Dr. Mariane Frieri, director of allergy and immunology at Nassau
Medical Center in East Meadow, said while the
premise of the study is intriguing, more research needs to be done.
"I am very much aware of the paradoxical effect here," said Frieri,
referring to animals as a source of protection, especially in
the face of medicine's longstanding insistence on shooing animals away from allergic children.
"I don't want anyone to get the notion that they can now go out and
buy 10 cats," Frieri said. "The issue here is exposure in the
first year of life."
Experts agree that the new study provides a foundation to move an
scientific notion called the hygiene hypothesis from
a good idea into provable theory. The decade-old hypothesis suggests that modern environments have become "too clean."
According to the theory, the immune system, primed throughout
to fight scourges since eliminated by antibiotics and
vaccines, now like a turncoat responds with allergies and asthma.
"It has only been within the past few years
we have seen a a few well-designed studies that begin to fit [the
hypothesis]. We think ours is one," Ownby said.
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