| Asphyxiation and its discontents

Why have asthma rates shot up in the last two decades?

According to the World Health Organization, childhood respiratory asthma is globally the most common chronic illness in children. It affects 20 per cent of the population, and incidence rates have shown no signs of decreasing in the last decade. In fact, in the 90s, incidence rates increased by an alarming 160 per cent in North America, according to the U.S. National Institute of Health. The reasons for this immense increase still perplex scientists.

Asthma is a chronic inflammatory disease of the lungs where airway tubes periodically and temporarily narrow in response to stimuli such as cold air, dust mites, exercise, perfume, allergens like pollen, viral infections like the common cold, and air pollutants. During an asthma attack, airway muscles constrict, the lining of the airways swell, and thick mucus fills the bronchial tubes, leading to symptoms that include wheezing, coughing, difficulty breathing, and/or chest tightness.

Dan Cooper, Director of the Institute for Clinical and Transnational Science (ICTS) at the University of California at Irvine believes that there are many reasons for the increase in asthma rates. “For one thing, great medical advances have allowed an increasing number of premature babies to survive,” he said. In these babies, the immune system is triggered more and the lungs have less time to develop properly, perhaps making them more prone to [lung] diseases. It might also have something to do with the recent increase in pollutants and pesticides in the air,” he said.

Christine McCusker, a pediatric allergist, and associate professor in McGill’s Department of Pediatrics, and a researcher at Meakins-Christie Laboratories, believes that the current statistical plateau in asthma incidence rates exists because physicians are becoming more adept at differentiating asthma from other respiratory diseases, such as viral-induced respiratory distress.

“Asthma has gone from a disease that physicians attributed to any condition that resulted in wheezing to a diagnosis that can only be made after a more comprehensive analysis of past medical history, frequency and duration of symptoms, trigger determination, and age considerations are made,” she said.

But diagnosis still remains difficult: people with asthma seem perfectly healthy between attacks even though their lung function is sub par. Also, patients cannot always determine why asthma attacks occur, or even predict when their next attack will occur. Unlike other diseases, such as HIV, sickle cell anemia, and tuberculosis, there is still no blood test to diagnose asthma. Though patient history, chest x-rays, sputum tests, and pulmonary function tests can point physicians towards asthma, they are still not conclusive.

Asthma also presents myriad symptoms that often overlap with other diseases. “Wheezing is associated with asthma, but can occur in patients with pulmonary edema or heart failure, and can also be triggered in healthy individuals given certain conditions,” says Cooper.

Hye-Won Shin a prominent researcher at ICTS, explains that even taking a proper patient history is problematic. “There are many children from low-income families who simply do not have the insurance to afford clinic visits [and medication]. [There] have been many reported cases of parents having to lie to clinicians about the severity of their child’s symptoms,” she said. However, treatment in Canada remains more accessible than in the U.S. “In Canada, you have the opposite problem in fact,” claims McCusker. “You have relatively easy access to care and most provinces have programs to supply [inhalers]. However, because of the huge number of prescriptions issued per year, it does become a costly disease to manage…”

Beside ambiguities in diagnosis, the controversial “hygiene hypothesis” may also explain why asthma rates have increased significantly in developed countries and not in developing countries. When a foreign substance attacks the body, an inflammatory response is initiated. However, any time the inflammatory response is stimulated, an anti-inflammatory response is also triggered to curb the initial response. This curbing response is developed more in countries where there is an exposure to a variety of pro-inflammatory triggers, such as viruses. In Western countries, because there is less exposure to such triggers in childhood, there is thought to be a deregulation and disruption of pro- and anti-inflammatory mechanisms, partly neutralizing the curbing response and rendering inflammatory diseases, like asthma, diabetes, allergies, and autoimmune disease more common.

McCusker has her own reaso why asthma and allergies are virtually absent in Africa. Individuals who could potentially have asthma symptoms often die before those symptoms appear “because access to medical care is much more difficult” than on other continents. “Either that or the immune systems is so busy fighting off malaria, schistosomiasis, sleeping sickness, and other infectious diseases, that asthma doesn’t even manifest,” she said.

According to McCusker, the hygiene hypothesis was originally theorized in 1995, and was formulated partly based on observations made after the collapse of the Berlin Wall. “Epidemiologists have had a field day since the wall came down,” she said. “Berlin was a relatively uniform population when the wall went up, since genocide had gotten rid of a lot of ethnic diversity. When the wall went up, it literally split the city in two, and so for about 40 years, there were people living in socioeconomic conditions that were almost polar opposites, but genetically, the people were similar. It was beautiful fodder for lots of studies,” she said.

When the wall came down, epidemiologists predicted that asthma and allergies would be rampant in East Berlin, where health care was relatively less accessible, people lived in overcrowded conditions, and infections were high. Instead, West Berlin was found to have higher asthma rates. Since the genetic populations of both West and East were relatively uniform, the argument maintained that environment, specifically hygiene, was making a difference. West Berlin had less viral diversity, and thus newborns’ immune systems were not conditioned to respond properly to certain stimuli.

Cooper believes in an exercise corollary to the hygiene hypothesis. In contemporary Western society, food is readily available and cheap. He believes that human beings, rather than working towards maintaining a balance between energy intake and energy expenditure, now tip the balance towards intake. “Physical activity also stimulates the immune system towards a response similar to the response that bacteria and viruses trigger,” Cooper said. “Because children are not as physically active as in the past, the immune system is not being triggered as much in childhood, perhaps also contributing to increased asthma rates.”

McCusker agrees that asthma is often associated with inactivity and thus, obesity. “It’s like a vicious cycle. People with asthma often have exercise limitations that make them less likely to be fit. This leads towards an increased risk of obesity. Fat cells release molecules that are thought to worsen asthma, and therefore asthmatics become even more exercise limited, and are less likely to engage in exercise,” she said.

As common as it is in the developed world, it is still a serious mystery in the scientific community what exactly constitutes asthma. Is it disease of the airways, or is it more a systemic disease of the whole immune system? To what extent do genetic and environmental factors play a role in causing asthma? Can diverse viral exposure in childhood have preventative effects? Why do some children respond to treatment and some do not? Until these fundamental questions about asthma are clarified, Cooper believes that the quality of life of children living with asthma may not increase significantly.