Asthma in Latin America: where the asthma causative/protective hypotheses fail

Abstract

protection have been the subject of challenges and changes during the last years. Probably the most important are related with the findings of large, well-standardized epidemiological studies undertaken at global scale which have included children from several countries in different stages of development and with diverse ethnic and cultural backgrounds1-3. These studies have provided information on largely ignored aspects related to asthma prevalence in low-resourced countries, and have shown that findings, conclusions and hypotheses based on studies from well-resourced countries are not globally applicable. Furthermore, they are widely insufficient to explain the peculiarities of the distribution pattern of asthma symptoms’ prevalence in the world. The consistent lack of representation of low-resourced and culturally diverse populations in past epidemiologic studies on asthma in children has subtracted global validity to their results and has been probably an important impediment for advancing in the determination of the etiopathogenic bases of the disease. The inadequacy and partiality of this developed-countries’ approach, has been recently shown by worldwide large and inclusive studies which indicate that several “truths” regarding asthma-related epidemiologic issues are not consistent and are probably applicable only to the minority of asthmatic children. The International Study of Asthma and Allergies in Childhood (ISAAC), the largest epidemiological study ever performed at global-scale, has consistently demonstrated a remarkable variability of current asthma symptoms in the different countries and regions of the world, high prevalence in developing countries, lack of universal application of hypotheses on causation (low proportion of asthma attributable to atopy), and protection (high prevalence of asthma in children living in developing localities and low hygienic standards), and an erratic relationship between air pollution (smog) and prevalence of asthma symptoms (low asthma prevalence in centres with heavy air pollution). In Latin America, a developing region where there was no regional comparative information of childhood asthma until the advent of ISAAC (13 years ago), it has been consistently found that several of its centres were among those with the highest prevalence of asthma symptoms in the world2,4,5. The high prevalence of asthma in developing countries has been simplistically explained as that in such localities there is a different type of asthma, mainly determined by infections or viral respiratory diseases and where allergy or atopy plays a very minor role. The concept that asthma is non-atopic in developing countries, and atopic in developed ones, has commanded the notions on asthma causality, at least from a first world perspective for a long time. This would be supported by the theory that the lack of stimulation of the immune system by agents and fac-