21 September 1998

Western Lifestyle To Blame For Asthma

At least 130 million people in the world suffer from asthma and 60 000 die each year. Heading the list are the industrialized countries. In the UK, 10 per cent of the population are estimated to suffer from this respiratory disorder, while the number of patients affected in the United States is increasing by 5 per cent a year. Experts meeting in Geneva for the 8th congress of the European Respiratory Society (ERS) lay the blame on house dust and relatively low exposure to microbial infections during childhood.

Because Anglo-Saxon countries are the most affected, researchers in the past have speculated that certain populations may be genetically prone to the condition. Recent studies have concluded that the risk of asthma is indeed transmitted from parents to children but this in itself is not enough to explain the increase that is occurring worldwide. Signs of allergy and asthma appeared much more frequently among grandchildren than in earlier generations, regardless of the status of the rest of the family. "These data need to be confirmed, but suggest strong and recent environmental pressure in the development of allergic airway sensitization", scientists at the conference concluded. "The distinction between high and low risk families may no longer be relevant for children of the asthma generation."

Asthma is defined as a form of chronic lung inflammation, brought about by hypersensitivity to allergens such as pollen, dust or animal hair. But attacks - when the airways inside the lungs contract, making it difficult to breathe - can be exacerbated by pollution, tobacco smoke, colds, cold temperatures, physical exercise, excitement or stress. But why is there less asthma in Asia and Eastern Europe than in western countries? Perhaps because western infants spend too much time shut up at home, in apartments contaminated by domestic dust mites. This is the view expressed in Geneva by Prof. Ulrich Wahn, of the Humboldt University in Berlin. With his team, he tracked over 1 000 babies during their first three years of life. In the course of the survey, the parents were twice given the task of passing a vacuum cleaner, fitted with a new bag, over exactly one square metre of carpet in their apartment. Then the bag was sent to the lab, where its content of mite excrements was estimated. It is these tiny particles, accounting for less than a thousandth of the total weight of dust, that cause the allergies. After many analyses of the health of the children and the composition of the dust, the researchers concluded that children who had developed allergies lived in flats where the dust contained on average 4 times more mite excrements.

Several speakers at the ERS Congress mentioned a different approach, involving the immune system. Today, Dr Erika von Mutius of the Munich University Pediatric Hospital and Stephan Weiland of the University of M�nster (Germany) presented the latest results of a comparative study carried out on 5 600 children aged 9 to 11, living either in Munich (former West Germany) or in Dresden (former East Germany). While the prevalence of hay fever is similar in the two cities (about 9.5 per cent), the figures for asthma differ considerably, with the western children the more affected (10.3 per cent in the west compared with 7.9 per cent in the east). Dr von Mutius notes that East German children are more likely to attend nurseries and to have more brothers and sisters. She believes that closer cohabitation with other children and their germs has the effect of stimulating their immune systems, and this could prevent the appearance of asthma. This theory is in line with the results of a Japanese study, published last year in the journal Science which concluded that children who develop a very strong immune reaction to the anti-tuberculosis vaccine BCG are less prone to asthma.

How can early childhood infections or vaccines provide protection against asthma? The answer seems to lie in specialized cells of the immune system, which are called T helper lymphocytes. "There are two types of these cells, Th1 and Th2", explains Dr Laurent Nicod of Geneva University, who chaired a workshop on Saturday focusing on the role of infections in pulmonary immunity. "For the immune system to work effectively, there has to be a balance between these two types of cells. Asthmatic children, however, tend to have an excess of Th2, which are known to be activated by allergic reactions. The solution therefore consists in restoring the balance between Th1 and Th2 by increasing the number of Th1 cells. This is where nature steps in rather conveniently, by causing Th1 activity to be triggered by bacterial infections such as tuberculosis, and hence also by the anti-tuberculosis BCG vaccine." It's possible that a vaccine similar to BCG could also be effective against asthma. "But we have not reached that point yet", concludes Laurent Nicod.