Sensitisation to three cockroach species in Southern Africa

Cockroaches are important allergen sources in many countries, especially in the tropics. Cockroaches produce several allergens that are major risk factors for rhinitis and asthma. Worldwide, the prevalence of cockroach sensitivity varies between 30% and 70%.Geographical differences exist with regard to cockroach allergen exposure and sensitivity within countries and between countries. No data are available for Africa in this regard. Currently the diagnosis of cockroach sensitivity in southern Africa relies mainly on the detection of specific IgE to Blatella germanica (German cockroach), while a number of other species are found close to human dwellings. The aim of this study was to investigate the prevalence and distribution of sensitisation to three different cockroach species among subjects residing in four different geographical regions in southern Africa. Strong IgE reactivity particular to B. germanica was found among subjects residing in Pretoria and Harare. By contrast strong IgE responses to other cockroach species, Periplaneta americana and Blatta orientalis, were observed in subjects living in Cape Town and Durban. The levels of specific IgE antibodies to all three cockroach species appeared to be higher in Cape Town than those from the other three cities investigated. Monosensitivity to all three cockroach species was observed and minimal cross-reactivity to house-dust mite. These data show that allergy to P. americana and B. orientalis are an important diagnostic consideration in temperate and coastal regions of southern Africa, whereas sensitisation to B. germanica appears to predominate in regions of higher altitude such as Pretoria and Harare.