The relationship between sensitisation to helminths and atopy, bronchial-hyperresponsiveness and allergic diseases may differ depending on many factors, including the genes of the population studied. We sought to examine this relationship in an African cohort.
Methods:
Urban Xhosa children were tested for ascaris IgE levels, bronchial hyper-responsiveness (BHR) by methacholine challenge, atopic sensitisation (skin tests to aeroallergens) and allergic disease (asthma, eczema and rhinitis) assessed by questionnaire.
Results:
Ascaris sensitisation was strongly associated with BHR but not with asthma, eczema or rhinitis. There was a dose-response relationship between increasing class of ascaris IgE and increased BHR (Prevalence ratio (PR) 1.75; CI 1.09-2.82). Higher levels of ascaris IgE were seen in those with BHR.
Ascaris IgE was associated with atopic sensitisation to aeroallergens. There was a dose-response relationship between increasing class of ascaris IgE and sensitisation to one or more allergen (PR 1.65; CI 1.27-2.13), sensitisation to house dust mites (HDM) (PR 1.79; CI 1.29-2.46) and grass (PR 2.66; CI 1.24-5.71) and number of positive skin prick tests (PR 1.78; CI 1.27-2.49).
Presence of any sensitisation to ascaris was associated with more than doubling the prevalence of HDM sensitisation (41.5% vs 18.5%) and almost quadrupling the prevalence of grass sensitisation (10.8% vs 2.8%).
Conclusions:
Ascaris sensitisation was strongly associated with BHR and with atopy, but not with allergic diseases. Possible explanations might be that the type of ascaris infection that causes high levels of ascaris IgE in this genetic population may also favour the development of atopy or that atopics in Africa have upregulation of their defence system against parasitic infection. These hypotheses are not mutually exclusive.