Indoor and outdoor allergens in Bloemfontein

Abstract

The Free State province of South Africa is traditionally considered to be a haven for outdoor allergens such as grass pollens, which cause severe hayfever symptoms in the grass pollen season, and maize pollens, particularly in the rural areas.In 1991 Mercer and Van Niekerk reported a house-dust mite skin-prick test positivity rate of 25.7% in an asthma clinic in Bloemfontein, 1 compared with a prevalence of 80% reported in children attending an allergy clinic in coastal Cape Town. on indoor and outdoor allergen sensitisation in the Free State. Not only does the study identify sensitisation to a previously unrecognised outdoor allergen (the spider mite, Tetranychus urticae) in the region, but it reports that the sensitisation rate to house-dust mites in patients with allergic rhinitis is a significant 46% for Dermatophygoides pteronyssinus and 44% to D. farinae using the ImmunoCap RAST.A second small acaralogical study by Sinclair et al. 4 of housedust mite species in Bloemfontein, also published in this issue of SAMJ, found house-dust mite in 50% of the homes investigated at some time of the year, and in 30% mites were present consistently.The finding of high levels of sensitisation to the spider mite Tetranychus, readily explained by the widespread prevalence of the mite in Free State farms referred to by Seedat et al., 3 has also been reported from the Hex River Valley in the studies of Jeebhay.5 Since many subjects sensitised to spider mite are simultaneously polysensitised to other outdoor and indoor allergens, the clinical significance of such sensitisation has yet to be studied by exposure and challenge studies. There are no vaccines available to desensitise patients to spider mites.In contrast, immunotherapy for house-dust mite allergens is available by the sublingual and subcutaneous routes for patients sensitised to D. farinae and/or D. pteronyssinus who do not simultaneously have other significant allergen sensitisations, on a named-patient basis. For patients in the Free State who have persistent rhinitis symptoms outside the pollen season related to the indoor environment, testing for specific mite indoor allergen sensitisation is very important, both for institution of allergen avoidance measures and selection of the appropriate mite-specific avoidance measures, and for selection of the appropriate mite-specific immunotherapy vaccine to offer the patient a chance of cure. It is interesting to note that Seedat et al.3 found that allergic subjects in the Free State who had previously lived at the coast were significantly more likely to be sensitised to mites than those who had not, emphasising the importance of history taking when selecting allergy test panels for the investigation of allergic patients.The acaralogical studies of Sinclair et al. 4 provide some insight into the variability of the presence of and therefore exposure to mites in Bloemfontein homes, and also illustrates that in some homes very high levels of mites are attained as a result of indoor microclimate factors that raise indoor...

Prevalence of Blomia tropicalis allergy in two regions of South Africa

“…The warm Mozambique current that flows along the coast is responsible for warmer seas, warmer temperatures and higher humidity. [7] This warm and humid climate is much like that in the subtropical belt and could explain the high prevalence of B. tropicalis along this coastline. A 2010 study in Mexico City, which does not have a temperate climate, showed B. tropicalis allergy to be highly prevalent in patients with allergic rhinitis and asthma.…”

“…[4][5][6] One study in the Durban region found the incidence of HDM allergy among asthmatics to be as high as 95%. [7] Worldwide, there are a number of HDM species involved in these atopic disease processes. These include Dermatophagoides pteronyssinus, D. farinae, Euroglyphus maynei and Blomia tropicalis.…”

Nutrition and allergic diseases in urban and rural communities from the South African Food Allergy cohort

“…South African indoor allergens include house dust mites, cockroaches, and pet dander. Der p is ubiquitous, but mite numbers are lower in inland areas with lower humidity . Der p sensitization is common in atopic South African children .…”

Aerobiology in South Africa: A new hope!

“…Most of the common global aeroallergens are found in South Africa, due to a variety of climates and biomes. 1 Non-native trees have been planted in South Africa to produce timber, for example eucalypt (Eucalyptus spp.) and pine (Pinus spp.)…”