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Dr. Thomas A.E. Platts-Mills on Allergen Avoidance through Environmental Control

Some medical professionals think of him as "Dr. House Dust Mite" because of his extensive, pioneering research in the field. Dr. Thomas A.E. Platts-Mills is Professor of Medicine and Microbiology at the University of Virginia. Since 1982 he has been head of the Division of Allergy and Clinical Immunology. Dr. Platts-Mills served as President of the American Academy of Allergy, Asthma & Immunology (AAAAI) from March 2006 to March 2007. Since 1974 he has been active in research on allergic disease and has published more than 300 papers.

In 1978, Dr. Platts-Mills and his research team purified DerP1, the first isolated allergen from dust mites.

"Two years later," says Dr. Platts-Mills, "we realized that the form in which the allergen becomes airborne is as dust mite feces and proved that the allergen becomes airborne just for short periods of time and then falls."

Dr. Platts-Mills explains that air filtration alone is not effective against dust mite allergen because the allergen does not stay airborne for long. When it comes to combating dust mites, it's more important to focus on their favorite hideout: your bed.

Allergen Avoidance through Environmental Control

"I think it's important to have a comprehensive, control plan and to outline to patients what you need to do and then create a list of priorities about how they go about it," says Dr. Platts-Mills. "And obviously the first thing is to cover the pillows and the mattress.

"And the next thing to do is to make sure that the bedding is either covered - that is, the duvet - or can be washed regularly. And then you move to the rest of the room, focusing on the bedroom first. Get rid of all the rubbish, and if possible, get rid of any upholstered furniture in the bedroom. If you can, get rid of the carpet and have a polished floor. But obviously it's very important to say to people that if they can't get rid of the carpet now, they'll plan to do it sometime in the future.

"You can then start thinking about the rest of the house, and a good move is to decrease the humidity. You definitely don't want to either work or live in a basement, and it's important to avoid basements if you can.

"So you decrease humidity in the whole house. You think about sofas and upholstered chairs elsewhere in the house; try and reduce those. I've seen patients with atopic dermatitis where their primary source of mite exposure in the house was clearly the sofa. The sofa had very high levels, and they'd lie on the sofa watching television, and that's their major source of exposure. You can't ignore rooms outside the bedroom, but the bedroom comes first."

Dust mite allergen is a particularly nasty allergen; approximately 80% of allergy sufferers are sensitive to dust mites. Furthermore, Dr. Platts-Mills and his research team have provided much evidence that dust mite allergen can play a causal role in the development of asthma.

Dr. Platts-Mills explains the power behind dust mite allergen: "We think that dust mite feces contain the allergen DerP1, which is a very potent allergen, but also contain endotoxin and bacterial DNA. Both of those interact with the immune system to increase the response. So we think that dust mite is such a 'good' allergen both because the proteins are what we call 'very foreign' and also because the allergen is delivered in this package which includes endotoxin and bacterial DNA."

Dr. Platt-Mills points out that, in terms of evolutionary distance, dust mite allergen is very foreign because it is about 600 million years away from us; whereas cat dander, for example, is only about 60 million years away from us. Dust mite allergen, then, is a more foreign protein to our immune systems.

The Rise in Allergies & Asthma: Hygiene Hypothesis & Lifestyle Factors

The hygiene hypothesis is an attempt to explain the increase in the prevalence of allergies and asthma in modern societies over the past few decades. The main idea is that we have become too clean and sanitary through exposing our young immune systems to fewer foreign bodies and thereby not giving the immune system a chance to fully develop.

Dr. Platts-Mills does not completely disagree with the hygiene hypothesis, but he thinks that there's more to the story: "The key moves in the hygiene hypothesis are probably clean water, wearing shoes, no animals in the house (no big animals in the house and not living on a farm, so you decrease endotoxin exposure), not having [parasitic infections], and not having malaria.

"The problem with the hygiene hypothesis is that in a place like New York, all of those things were finished by 1920. Now, you can argue that hay fever started to increase back in 1910 and was already epidemic by 1940, by the beginning of the second world war. A lot of the hygiene hypothesis was designed to explain the rise in asthma. The rise in asthma didn't start until 1955 or 1960. My actual summary of what I think happened: Yes, you need cleanliness in order to get allergy, but the rise in asthma from 1960 onward, which was occurring among allergic patients, is much more likely to be due to the major change in lifestyle that occurred then, which is that we moved indoors and have essentially become an indoor species.

"In the 1950s, children would spend three hours a day outdoors playing. From about 1960 onward, that's progressively decreased so that now it's unusual for children to go outdoors. The outdoor exposure could be beneficial because it allows the children to open up their lungs and exercise their lungs; it could be beneficial because they don't get so fat; it could be beneficial because their environment is better; or even, as has recently been suggested, because they get more exposure to the sun and therefore aren't Vitamin D deficient.

"It's recently been proposed that going indoors decreased sun exposure so much that children are effectively Vitamin D deficient. I don't think that's the explanation, but it's a very interesting idea."

Our whole lifestyle changed when we became a modern "indoor species" as Dr. Platts-Mills says. We suddenly experienced a drastic decrease in exposure to sunlight and foreign proteins in nature, an increase in exposure to certain indoor allergens like dust mites, and a decrease in exercise and overall fitness.

At the same time, the design of tightly sealed modern homes often breeds allergens.

"Obviously the design of houses has become much warmer, much tighter, with fitted carpets, and more upholstered furniture," says Dr. Platts-Mills. "In some places in the world, those changes have dramatically increased the growth of dust mites."

Visit the American Academy of Allergy, Asthma & Immunology to learn more about Dr. Platts-Mills, dust mites, and environmental control of allergens.

Originally published in the May 2007 issue of Allergy Consumer Report.

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