Essay Asthma in Africa Matthias Wjst*, Daniel Boakye Whatever does not exist does not have a name (African proverb). An ew survey conducted by Emmanuel Addo-Yobo and colleagues, and published in PLoS Medicine [1], shows an increase in the prevalence of asthma and allergic diseases in children in Ghana between 1993 and 2003. In this essay, we discuss the context for this new study by exploring what is known about the epidemiology of asthma in Africa. Research on Asthma in Africa Looking at about 120 papers from Medline on asthma in Africa, we found that asthma research is currently dominated by authors from South Africa, followed by authors from Nigeria, Tanzania, Ethiopia, Kenya, doi:10.1371/journal.pmed.0040072.g001 and The Gambia. Most are case studies, closely followed by cross- Figure 1. Hookworms (Ancylostoma caninum) Attached to the Intestinal Mucosa sectional studies, and then case-control Barely visible larvae penetrate the skin (often through bare feet), are carried to the lungs, migrate studies. There have been very few through the respiratory tract to the mouth, are swallowed, and eventually reach the small intestine. cohort studies. Only a few studies use This journey takes about a week. (Photo: Centers for Disease Control) objective measures [2,3], which makes the new PLoS Medicine study unusual, kerosene heating, grass mats, mud and (ISAAC, http:⁄⁄isaac.auckland.ac.nz) since the researchers used repeated cow dung, smoking, and car and truck in which seven African countries measurements of skin prick tests and diesel exhaust. In the occupational participated (English-speaking regions: bronchial reactivity [1]. setting isocyanate and latex sensitivity Ethiopia 9.1%, Kenya 15.8%, Nigeria have been reported as risk factors, 13.0%, and South Africa 20.3%; and Clinical Features and Risk Factors and poultry workers, hairdressers, French-speaking regions: Algeria The clinical presentation of asthma in gold miners, and wood choppers are 8.7%, Morocco 10.4%, and Tunisia Africa does not seem to be different reported as having an increased risk of 11.9% [9]). Symptom rates are lower from other parts of the world [4], asthma. Annual rainfall seems to have although one study reports later an infl uence on symptom presentation. disease onset in Africa [5]. Assumed Despite the risk factors discussed Funding: The authors received no specifi c funding risk factors are local fl ora such above, there is no overall hypothesis to for this article. as Kikuyu grass, Makaore cherry, explain asthma causation in Africa. In Competing Interests: The authors have declared Tanganyika aningré, and Der néré one study, traditional healers in Dar that no competing interests exist. as well as helminthic infection by es Salaam, Tanzania were convinced Citation: Wjst M, Boakye D (2007) Asthma in Trichuris, Schistosoma, Ascaris, and that asthma is caused by “ingestion of Africa. PLoS Med 4(2): e72. doi:10.1371/journal. pmed.0040072 hookworm (Figure 1). Well-known amniotic fl uid during birth” (83%), allergens in Africa are house dust mite, by “God” (75%), or “one inherits Copyright: © 2007 Wjst and Boakye. This is an cockroach, and cat and dog dander; [asthma] from parents” (73%) [6]. open-access article distributed under the terms Traditional asthma remedies are of the Creative Commons Attribution License, a less well known allergen is washing which permits unrestricted use, distribution, and soap. Parental history, female sex, low usually tried without major success reproduction in any medium, provided the original physical activity, and malnutrition, have [7] although some may contain author and source are credited. been described as risk factors together pharmacologically active substances Matthias Wjst is with the Institut für Epidemiologie, with pesticides, insecticides, wood or [8]. GSF–Forschungszentrum für Umwelt und Gesundheit, München-Neuherberg, Germany. Prevalence Rates Daniel Boakye is with the Parasitology Department at Noguchi Memorial Institute for Medical Research, Intercountry prevalence data are University of Ghana, Accra, Ghana. The Essay section contains opinion pieces on topics limited to the International Study of of broad interest to a general medical audience. * To whom correspondence should be addressed. Asthma and Allergies in Childhood E-mail: m@wjst.de PLoS Medicine | www.plosmedicine.org 0203 February 2007 | Volume 4 | Issue 2 | e72 than in industrialized countries, while before reaching reproductive age. [27]. We believe that this shift might be only South Africa approaches rates Vaccination programs, better nutrition, even in the interest of the developed found in the UK. The interpretation and antibiotic treatment, however, countries that are now suffering of these fi gures, however, is diffi cult; have reduced mortality from acute from high rates of asthma [9], since there might be an increase with gross respiratory infection while the asthma major characteristics of traditional domestic product and industrialization incidence increased at the same time. lifestyle have changed irrespective of factors [10]. Rural African regions Safe water [14] and antibiotic use socioeconomic status. Many African always showed much lower asthma [22] could therefore be indicators of societies are still going through prevalence rates than urban areas [11]. a suppression of natural or purifying the early stages of the transition to People living in rural grasslands rarely, selection. urbanised economies, leaving us all if ever, suffer from allergic diseases This suppression may have enormous opportunities to look for the factors and some do not even have a term to consequences on a population level: driving early sensitisation and later describe this condition [12]. In Europe, mortality under the age of asthma [27]. In that respect Africa 5 years was about 250/1,000 live-born probably has more to offer than any Genes or Environment? children in 1900, dropped to 50 around study in the developed world.  As in industrialized countries asthma 1950, and is now about fi ve [21]. In in Africa is determined by genes and sub-Saharan Africa in 2000, there are Supporting Information environment. However, both genetic still 175 deaths per 1,000 live births Alternative Language Text S1. Translation and environmental effects may operate [15]; Addo-Yobo et al. report a decline of article into German by Matthias Wjst in different directions and on different from 69/1,000 to 55/1,000 live births Found at doi:10.1371/journal. pmed.0040072.sd001 (102 KB DOC). scales. during the study period [1]. Can these The African environment is different differences in childhood mortality from that in other parts of the world— explain the extremes of virtually no Acknowledgments in Africa, not only climate but also air asthma up to a prevalence of 20%? To Dr. John Britton and both reviewers pollution reaches both extremes [13]. This seems a testable hypothesis where for comments on an earlier version of the The spectrum of pathogens may also even the rise or fall of gene variants manuscript. be different, with confl icting evidence in immune defence genes could be References on worm infection, IgE, and allergy. monitored. Or do environmental 1. Addo-Yobo EOD, Woodcock A, Allotey A, Recent research in Ethiopia concludes factors play a central role? Or is this Baffoe-Bonnie B, Strachan D, et al. (2007) Exercise-induced bronchospasm and atopy that “There was no reduction in the increase a complex melange of all of in Ghana: Two surveys ten years apart. risk of AD [atopic dermatitis] in the variables? PLoS Med 4: e70. doi:10.1371/journal. pmed.0040070 relation to intestinal parasite infection; As of the 1980s, there was an 2. Keeley DJ, Neill P, Gallivan S (1991) in fact, AD was increased in subjects overall conviction that asthma Comparison of the prevalence of reversible with Trichuris .... 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