Urbanization and childhood asthma: An African perspective☆,☆☆
Section snippets
URBAN-RURAL DIFFERENCES
In Africa, as on other continents, the prevalence of asthma varies from country to country and among relatively small geographic areas within countries. Epidemiologic studies largely using exercise challenge tests in study populations have shown the prevalence of exercise-induced bronchospasm (EIB) to be greater among children living in urban areas than in rural areas (Table I).3, 4, 7, 8
Reference Country Region or group No. Age range (y) Prevalence (%) Van Niekerk et al3
EARLY-LIFE EVENTS AND ASTHMA
Besides differences in the living environment, lifestyle, and outdoor pollution as possible explanations for the difference between urban and rural asthma prevalence, other factors may also play a role. These factors include a family history of allergy and asthma more likely to be found in urban centers because of the greater prevalence of asthma in these populations.7 It is possible that there is an increased susceptibility for asthma in urban compared with rural African children. Much
PARASITES AND ASTHMA
Parasite infestation, especially with roundworms such as Ascaris lumbricoides, was once thought to be responsible for the low rates of childhood asthma reported in African studies during the 1970s. The postulated mechanism was an increased IgE response to parasites and a blocking of receptor sites. Godfrey18 proposed that parasite-induced IgE may prevent the development of atopic disease. This hypothesis depends on the fact that binding of specific IgE to mast cells and basophils is necessary
OTHER FACTORS
Although the Ethiopian study11 showed a greater response to skin tests for house dust mite in the rural sample compared with the urban sample (11.8% vs 4%), there is little information on mite exposure in urban and rural areas in other African countries. In Ghana8 there was a significantly great response to skin tests for house dust mite in the urban areas compared with the rural areas. The majority of the information on house dust mite comes from urban settings in Africa. In Zambia asthma is
THE FUTURE
Future studies in Africa will need to focus on early life events including infections (bacterial, viral, and parasitic), the effects of early exposure to potent indoor allergens such as house dust mites and diesel exhaust pollution29 (urban and rural), and the increasing use of agricultural pesticides in rural areas. Factors that have also not as yet been investigated in Africa include the effects of the role of sibship size,30 the introduction of new bedding materials,31 the early use of
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Reprint requests: Eugene G. Weinberg, MBChB FCPaeds(SA), Allergy and Asthma Clinic, Red Cross Children’s Hospital and Institute of Child Health, University of Cape Town, Rondebosch 7700, South Africa.
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0091-6749/2000 $12.00 + 0 1/1/104384