Allergic diseases are distributed worldwide and their risk factors and triggers vary according to geographical and socioeconomic conditions. Allergies are frequent in the Tropics but aspects of their prevalence, natural history, risk factors, sensitizers and triggers are not well defined and some are expected to be different from those in temperate zone countries. The aim of this review is to investigate if allergic diseases in the Tropics have particularities that deserve special attention for research and clinical practice. Such information will help to form a better understanding of the pathogenesis, diagnosis and management of allergic diseases in the Tropics. As expected, we found particularities in the Tropics that merit further study because they strongly affect the natural history of common allergic diseases; most of them related to climate conditions that favor permanent exposure to mite allergens, helminth infections and stinging insects. In addition, we detected several unmet needs in important areas which should be investigated and solved by collaborative efforts led by the emergent research groups on allergy from tropical countries.Electronic supplementary materialThe online version of this article (doi:10.1186/s40413-016-0110-7) contains supplementary material, which is available to authorized users.

There is cross-reactivity between Ascaris and mites, determined by several allergens including tropomyosin and glutathione-S-transferase. In addition to its potential impact on asthma pathogenesis, Ascaris infection and mite allergy diagnosis relying on the determination of specific IgE could be affected by this cross-reactivity. ABA-1 has no cross-reactive counterpart in mite extracts, suggesting its usefulness as a more specific marker of Ascaris infection.

Fifty dust samples were collected from the mattresses and bedroom floors of 25 subjects with allergic asthma in Cartagena, Colombia, in order to identify house dust mites and quantitate Der p I, Der f I and Blomia tropicalis allergens. The geometric mean of the total mite density per gram of dust was 418 (range, 40-2280). Twenty-two samples (44%) had more than 500 mites and four, less than 100. B. tropicalis and Dermatophagoides pteronyssinus were found in 96% and 90% of the samples, accounting for 40.1% and 35.7% of the total mites, respectively. Cheyletus malaccensis, Chortoglyphus arcuatus, Pyroglyphus africanus, Oribatids, Grallacheles bakeri, Tarsonemus spp., Suidasia spp., Dermatophagoides farinae and unidentified mites accounted for the rest. The geometric mean of the total mites/gram of dust in mattresses (563.9) was significantly higher than in floor dust (309.1), P < 0.01. Allergen concentrations and mite numbers were analysed by Spearman rank correlations: B. tropicalis mites vs B. tropicalis allergen, r = 0.54, P < 0.001; D. pteronyssinus mites vs Der p I, r = 0.52, P < 0.001. A negative correlation was obtained between B. tropicalis mites and Der p I. Allergens derived from B. tropicalis and other domestic mite species may play an important role in sensitization and allergic symptoms in Cartagena, Colombia.

To characterize the allergens of Blomia tropicalis, a cDNA library was constructed and screened with allergic sera from asthmatic patients. One clone, Bt6, was subcloned and sequenced. The nucleotide sequence of 934 bp length shows a 390-bp reading frame which encodes a 130-amino acid protein with a MW 14.8 kD. No potential glycosylation site was found in the predicted protein. The inferred amino acid sequence has no homology to known allergens. It has a cyto-solic fatty acid-binding protein (FABP) signature at 5–22 amino acid residues, 42.3% identity with the Sm14-FABP of Schistosoma mansoni and 36% identity with FABPs from rat, mouse, bovine and human. The protein was expressed as a GST fusion protein and the purified GST-Bt6 used for dot blot, RAST and RAST inhibition assays. The frequency of IgE binding of allergic sera to Bt6 was low (11%) and usually weak. One positive serum did, however, show strong reactivity by RAST and dot blot and Bt6 could inhibit 60% of the IgE binding of this serum to the B. tropicalis extract. These data show that Bt6 encodes a mite FABP with allergenic properties, which are pronounced in some atopic subjects.

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