Urbanization and childhood asthma: An African perspective,☆☆

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Abstract

The increasing prevalence of childhood asthma in the developed world is a cause for concern. Much research is currently being conducted in an attempt to identify possible reasons for this occurrence. A so-called Western lifestyle has been the factor most commonly cited to explain this worrying increase in asthma prevalence. In essence, this implies a way of life where children are exposed from early infancy to a wide range of foods, infections, indoor and outdoor allergens, and irritants and to the effects of motor vehicle pollution. Until fairly recently, children in many African countries lived mainly in rural areas and were not exposed to the effects of a Western lifestyle. Early studies in a limited number of African countries showed a very low rural prevalence of childhood asthma, especially where children lived according to a traditional lifestyle. These same studies showed that asthma was not uncommon in urbanized African children. There has been an increasing tendency over the past 20 years for those in rural communities to move to the large urban centers. More recent childhood asthma prevalence studies, especially those from Kenya and Ghana, have confirmed the urban-rural differences but have shown a much narrower gap. In part this may be the result of exposure of rural children to agricultural pesticides and irritants as well as of an increasing tendency to adopt a more Westernized lifestyle such as the use of beds with mattresses, pillows, and blankets. These circumstances on the African continent provide a natural laboratory in the quest for factors that influence the development of asthma in susceptible children. Once more fully elucidated, it is possible that much valuable information will be available to combat the relentless increase in childhood asthma both here as well as in the developed world. (J Allergy Clin Immunol 2000;105:224-31.)

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

. EIB in African children

ReferenceCountryRegion or groupNo.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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  • Cited by (0)

    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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