Risk factors for asthma in urban Ghana

Childhood asthma

Asthma is the most common chronic disease of childhood. Despite increasing evidence indicating that genetic and environmental factors have significant effects on airway development and function in early life, our understanding of the natural history of the disease is limited. The development of objective outcome measures will enable us to distinguish between children with transient early wheeze and those who will progress to persistent asthma, and to investigate factors affecting airway function throughout early childhood. A thorough knowledge of lung physiology in early life and its relationship with environmental exposures and prior or subsequent development of asthma would have a profound effect on our understanding of the natural history of asthma and the design of future strategies for disease prevention.

Early pet exposure: friend or foe?

PURPOSE OF REVIEW

Sensitization to pets is a risk factor for asthma and it was assumed that pet ownership was a risk factor for sensitization. Epidemiological studies failed to confirm this, some even suggesting that keeping pets decreased the risk of sensitization and asthma. In the last year, 10 studies have been published which have, at least in part, attempted to address the question. The results, however, are heterogeneous and it is still not clear how we should advise our patients on this issue of pet ownership.

RECENT FINDINGS

Results of studies of the association between exposure to cat or cat allergen and the development of sensitization are such that almost any view on the relationship could be supported by evidence from the literature. For dogs, there are fewer data, but there is little to suggest that keeping a dog increases the risk of sensitization to dog. The majority of studies reviewed find either no association or a reduced risk of asthma amongst pet owners, but only one of these selectively excludes those who deliberately avoid pets from the analysis. There is evidence to suggest that amongst non-pet owners, the risk of sensitization and of asthma increases in areas with a high proportion of pet owners. There is evidence emerging that the effect of exposure to pets may be different in different relative risk groups, based on parental allergy. There is also evidence that asthma is more severe amongst pet sensitized pet owners.

SUMMARY

There are several large birth cohort studies being conducted around the world designed to measure the development of asthma and allergies in children with prospective and objective measures of environmental exposures. The results of such studies are required before the association between pets and asthma can be determined.

Inhalant allergies in Zimbabwe: a common problem

Allergic rhinitis, allergic conjunctivitis, allergic asthma and atopic dermatitis affect a quarter of the population of the industrialised countries and are the most common symptoms of type I hypersensitivity reactions. Their prevalence has been documented in many communities, yet data from Africa are limited. In the 5-year period from September 1997 to September 2002, approximately 14,000 patients of all ages were referred to the only specialist allergy clinic in Harare, Zimbabwe, for allergy investigation, diagnosis and therapeutic management. In approximately one tenth of these patients, food allergies were diagnosed; less frequent presentations included allergic pharyngitis, bee- or wasp-induced reactions and latex allergy. An allergologic basis for the clinical conditions was established following a careful clinical and physical examination, evaluation of family history and the detection of in vivo (skin prick test) or in vitro (radio-allergo-sorbent test; RAST) allergen-specific IgE antibodies to known sources of inhalant allergens, using commercial allergen extracts and a RAST assay kit. Asthma diagnosis was supported by the clinical and laboratory findings of salbutamol-reversible airways obstruction. Case files of the first 1,046 patients are reviewed in order to define the clinical presentation of allergic patients in this region. It is highlighted that allergy in general and inhalant allergy in particular are very common, if not widely acknowledged, clinical problems in this Central African region.

The effect of allergen exposure in early childhood on the development of atopy

While there is good evidence for the association between allergen exposure and disease severity in sensitized individuals, and allergen exposure and development of sensitization, the relationship between allergen exposure and development of allergic disease is as yet unresolved. A protective effect of cat ownership on sensitization and allergic disease has been reported. The dose-response relationship between allergen exposure and sensitization may be different for different allergens (eg, linear for mite, bell-shaped for cat). Exposure to a high level of cat allergen may result in a modified Th2 response characterized by the presence of IgG4 antibody to cat proteins without IgE response, which could be regarded as a form of tolerance. The long-term prospective follow-up of well-defined cohorts with objective exposure and outcome measures will elucidate the complex relationship between environmental allergen exposures, sensitization, and asthma.