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(The online version of this article appears in three parts. Click here to go to part one or part three.)

Roaches and Dust Mites

SCHROEDER dropped me off at the Albert Einstein College of Medicine, where I was to meet David Rosenstreich, a professor of medicine, the director of the division of allergy and immunology, and one of the country's leading experts on asthma allergens. Rosenstreich had just returned from a meeting in Colorado, where he had delivered a lecture on cockroaches and asthma symptoms; he published what is widely regarded as the definitive study on the subject in a 1997 issue of The New England Journal of Medicine. He showed me slides of three of the 300 known cockroach species. Under magnification they appeared monstrous. "Wherever people go, from the Arctic to Antarctica, there are roaches," Rosenstreich told me. "They are really difficult to get rid of, particularly in multiple-family dwellings, because when you clean out one apartment, they simply move on to the next one, and then, when the coast is clear, they return." Children in infested homes are much likelier to show an allergic reaction to cockroaches than children who grow up without them, and are much likelier to have asthma attacks triggered by exposure to them. Rosenstreich said that roaches are by no means the only culprit. Fecal material produced by dust mites is also extremely allergenic, and given that dust mites require only heat, humidity, and dust (the major component of which is shed human skin) to survive, they are just as hard to get rid of as cockroaches. "Every square meter of mattress has twenty-four dust mites, and each dust mite produces seven fecal particles a day," Rosenstreich told me. "There's a quarter of a million fecal particles in every ounce of mattress dust. So you can see the difficulty."

Many homes in and around Hunts Point and other inner-city neighborhoods have all the qualities associated with high asthma rates: poor ventilation, uncontrollable heating systems, and water damage that leads to the growth of molds, which are another important allergen. Carpets, Rosenstreich said, are breeding grounds for all sorts of nasty things, as are upholstered furniture and the piles of clothes that tend to accumulate when many people crowd into tight quarters without sufficient storage space. "Five or more might share an apartment with a single bedroom," he said. "When you have so many crowded into such a tight space, you have lots of people showering, cooking, boiling water. That adds to the humidity, which of course is great for roaches."

Given the association of cockroaches and dust mites and mold with asthma, it may seem paradoxical that outside the United States asthma is a disease of affluence. There is, for example, almost no asthma in rural China or sub-Saharan Africa (apart from South Africa), yet it is rampant in Sweden and New Zealand and Australia. One possible explanation is that rugs and upholstery and other items in which insects might want to nest are still luxuries in the developing world. This theory begins to break down, however, when one considers that there are plenty of dust mites and cockroaches in rural China, and that Australians are not notably partial to upholstery or wall-to-wall carpeting. More likely, cockroaches and dust mites and diesel fumes and tobacco smoke and dog hair and mold and any number of other things are triggers of asthma -- but they do not cause it. Spending nearly all of one's time in a poorly ventilated home, as many inner-city American children do -- will surely aggravate asthma, but will probably not bring on the disease in someone not prone to it. What will bring it on? That, says Louise Cohen, the director of the New York City Childhood Asthma Initiative, is "the sixty-four-thousand-dollar question."

Immunity and Genes

ONLY recently have we understood what asthma is, let alone what causes it. Asthma was traditionally considered a simple allergic reaction that provoked spasms and constriction of the bronchial passages, resulting in wheezing and shortness of breath. But over the past twenty years it has become clear that although asthma attacks are episodic, the inflammation associated with them is chronic, and requires long-term management with anti-inflammatory medication -- in some cases for life. Scientists now believe that this chronic state is brought on by something that prevents the immune system from developing properly in the first months of life.

Starting out life with a naive immune system is not a bad thing. Were a fetus to have a mature immune system, it would almost certainly regard the mother as a foreign invader and reject her. A baby is protected for some time by antibodies passed to it through the placenta and, later, in breast milk. At about three months the immune system begins to mature in most infants. But in people who go on to develop asthma, the immune system seems to mature too slowly to be able to differentiate between annoying and serious irritants. As a result, the infant's system musters an armada of antibodies to fight cockroaches or dust mites as though they were deadly microbes. This results in an allergic reaction that constricts the airways and leads to hyper-responsive, or "twitchy," lungs (asthma means "panting" in Greek). Not all infants with twitchy lungs show symptoms to the same degree; it is thought that the minority of asthmatics who develop the disease later in life may actually have had mild, undetected asthma from early infancy. In severe asthmatic episodes a minor irritant can set off an immune response that shuts down the airways completely, resulting in respiratory arrest and, in extreme cases, death. Richard Green, the chancellor of the New York City school system, died in such an episode eleven years ago.

Fernando Martinez, the director of respiratory sciences at the University of Arizona, trained in Italy as a pediatrician but decided to do research on asthma when he realized how many of his patients had it. "It was extraordinary, a huge problem," he told me recently. "Like most people, I assumed tobacco smoke and pollution were the problem -- this was the politically correct way to think. But these factors turned out not to play a major role. In high-pollution areas, in low-pollution areas, among all ethnic groups, there was asthma. Clearly, something else was involved."

Martinez, who came to the United States after launching his career in asthma research, is one of a number of specialists who believe that modern life may be responsible for the developed world's asthma rates -- but in a very unexpected way. It is not tobacco smoke or pollution that is at the heart of the problem, these specialists believe, but modern hygiene practices and antibiotics that foreclose the need for the young immune system to tackle microbial and parasitic challenges. "Just as you need to use your eyes to develop sight and your legs to develop the muscles to walk," Martinez said, "your immune system develops through its experience. By legitimately protecting our kids from dangerous infections we may have kept parts of their immune systems from maturing."

This could explain why children in the developing world, who are repeatedly infected by bacteria and parasites, are unlikely to contract asthma, whereas children in the developed world, who are inoculated against infectious diseases and frequently given antibiotics, are contracting asthma in ever greater numbers. (Martinez quoted estimates that an astonishing 40 percent of children in the United States are given antibiotics for a period of a month or more in their first year of life.)

Yet most children in the United States do not get asthma, probably because most do not have the genetic constitution for it. It is well known that African-Americans and Hispanic Americans have a significantly higher rate of asthma than Caucasian Americans, and that this is at least in part a consequence of genetic predisposition. African-Americans on average have a smaller lung capacity than Caucasians, for example; some scientists think this increases their asthma risk. It is very difficult to determine which factors in these groups may have a genetic underpinning and which are caused by something other than genes. Hispanics and African-Americans tend to have relatively high rates of premature birth, for example, which might predispose infants toward asthma.

Carole Ober, a professor of human genetics at the University of Chicago, has made a relatively homogeneous group, the Hutterites of South Dakota, a focus of her asthma work. The Hutterites are members of a religious sect that began in the Tyrolean Alps in the 1500s. In the 1870s a group emigrated to what is now South Dakota. For the past fifteen years Ober has studied 1,500 of their descendants, all of whom can trace their heritage to sixty-four ancestors. Of the 750 with whom her asthma work is concerned, all live on nine communal farms, nearly all eat a high-fat diet, and none smoke. Most mothers in this group breast-feed their newborns for at least nine months. None of this is surprising in a religious sect with Western European roots. What is perhaps surprising is that roughly 15 percent of these Hutterites have asthma -- the same rate found in poor inner-city children in a related study in Chicago.

Because the Hutterites are genetically homogeneous, Ober and her team have been able to compare the genetic material of those who have asthma with material from those who don't, and to distinguish several genes associated with the disease. Ober has studied the genetic material of her Chicago population for similarities. So far, the genes linked to asthma in the Hutterites appear also to be associated with asthma in the Chicago population. The disease differs greatly between the two groups, however, in terms of symptoms. Asthma in the Hutterites is mild -- so mild that before Ober's study it often went unnoticed and undiagnosed. Very few Hutterites require steroids, a fairly routine treatment for moderate to severe cases elsewhere. And even fewer are hospitalized for the disease.

Ober and her colleagues have tried to tease out what it is about the Hutterites' lives that makes their experience of asthma so much less traumatic than that of urban dwellers. The ways of life differ dramatically, of course, but what stands out is that Hutterites live close to nature and far from the stresses of the modern world. It has long been observed that stress can bring on asthma attacks. Perhaps even more important is that although Hutterite homes are typically immaculate, Hutterite living compounds are not. They are full of the sort of dirt one finds in other places not covered by concrete and asphalt. Recent research suggests that living close to the soil and to the animals associated with farm life is protective against asthma attacks.

"The data in support of a protective effect [of farm animals] are looking increasingly good," says Patrick Holt, an immunologist who specializes in asthma at the TVW Telethon Institute for Child Health Research, in West Perth, Australia. "Such stimuli may aid in the normal postnatal maturation of the immune system and help it to correctly program immune responses against other agents, such as environmental allergens." This is perhaps why the Hutterites, who rely on farm animals for their livelihood, do not have life-threatening asthma despite their genetic predisposition to the disease. Although members of the sect do take antibiotics and are inoculated against childhood infections, their immune systems may benefit from early and frequent exposure to the parasites and microbes associated with farm animals. Evolutionarily speaking, this seems ideal: an immune system so vigilant that it is poised to overreact but whose responses are tempered by gentle exposure to the everyday grunge of the natural world.

Such exposure is certainly not what most Western parents desire for their children. "If there is one thing that characterizes American culture, it's obsessive cleanliness," says Scott Weiss, a pulmonary epidemiologist and the chief of environmental and respiratory epidemiology at Harvard University's Channing Laboratory. "There may be some optimal timing when exposure to infection should occur, but because parasitic infection is so uncommon in the Western world, and other infections are prevented with vaccines or squashed by antibiotics, we're essentially preventing children from getting that exposure."

Continued...

(The online version of this article appears in three parts. Click here to go to part one or part three.)


Ellen Ruppel Shell is a correspondent for The Atlantic.

Copyright © 2000 by The Atlantic Monthly Company. All rights reserved.
The Atlantic Monthly; May 2000; Does Civilization Cause Asthma? - 00.05 (Part Two); Volume 285, No. 5; page 90-100.