Are you allergic to Blomia tropicalis?

Latin name: Blomia tropicalis
Source material: Whole body culture
Family: Glycyphagidae
Sub family: Acari
Common names: Storage mite, Flour mite, Grain mite

Geographical distribution

Blomia tropicalis, a Storage mite, was earlier found predominantly in agricultural environments but is now being recognised as an important contributor to the allergen content in house dust in indoor urban dwellings.
B. tropicalis is a notable mite species in many parts of the world, and the most common and most important mite species in tropical countries. B. tropicalis and Dermatophagoides pteronyssinus occur in a significant percentage of homes in tropical and subtropical regions of the United States and Europe, and in Central and South America and Asia, along with the House dust mites Euroglyphus maynei and Dermatophagoides farinae. Blomia tropicalis is the 4th most common mite in the United States.

Unexpected exposure

Mites were found in 21% of 571 samples of cereal-based food products purchased at food retail outlets in the UK, and in 38% of 421 samples, derived from the 571 samples, which were examined after 6 weeks of storage in volunteers’ homes. The most common species were A. siro, T. putrescentiae, L. destructor and G. domesticus.

Allergens
In a study of 60 Taiwanese patients, B. tropicalis extract was shown to contain at least 30 protein components. The most frequently detected allergens were proteins with molecular weights of 14.3, 106.5, 94.0, 72.0, 91.9, 63.7, 100.3, 43.6, 27.3, 62.0, 34.7, 18.3, 41.1 and 21.9 kDa. The frequencies of IgE binding of 60 patient sera to those proteins were, respectively, 87.0, 65.2, 56.5, 43.4, 39.1, 39.1, 34.8, 30.4, 30.4, 17.4, 17.4, 17.4, 13.0 and 8.7%.

In a study investigating the IgE reactivity of allergens present in extracts of B. tropicalis and comparing the IgE responses to these allergens in asthmatics and patients with atopic dermatitis and allergic rhinitis, as well as in 199 non-atopic volunteer controls, 18 out of 29 protein bands present in Blomia extracts were recognised by the allergic and control sera. Of these allergens, 4 showed a high IgE binding frequency; these had molecular weights of 104, 80, 68 and 14 kDa. The 14 kDa allergen demonstrated the highest IgE binding frequency. The authors concluded that extracts from pure bodies of B. tropicalis contain 1 immunodominant and 3 important allergens.

At least 23 IgE-binding components have been demonstrated for B. tropicalis. 

The following allergens have been characterised:
Blo t 1, a Group 1 mite allergen, a cysteine protease, a major allergen, and a homologue of Der p 1.
Blo t 2, a 14.5 kDa protein, a Group 2 mite allergen

Blo t 3, a Group 3 mite allergen, a trypsin like protease

Blo t 4, a Group 4 mite allergen, an alphaamylase

Blo t 5, a 14 kDA Group 5 mite allergen, a homologue of Der p 5.

Blo t 6, chymotrypsin, a protease

Blo t 7

Blo t 8, a glutathione-S-transferase

Blo t 9, a collagenolytic serine protease

Blo t 10, a tropomyosin
Blo t 11, a Group 11 mite allergen, a paramyosin
Blo t 12, a 14.2 kDa protein
Blo t 13, a Group 13 allergen, a fatty acid binding protein
Blo t 14
Blo t 15, a chitinase
Blo t 18, a 60 kDa protein, a chitinase
Blo t 19
Blo t 20, an arginine kinase
Blo t 21
The following recombinant allergens have been produced to date: 
rBlo t 3
rBlo t 5
rBlo t 12
rBlo t 13

Recombinant Blo t 1 has been shown to have a 90% frequency of reactivity with IgE in sera from asthmatic children and a 65% frequency in sera from asthmatic adults, indicating that it represents a major allergen. Cross-reactivity between the Group 1 mite allergens of B. tropicalis (Blo t 1) and D. pteronyssinus (Der p 1) was demonstrated to be low.

Of 80 B. tropicalis-sensitive Taiwanese patients, 7% were allergic to Blo t 2. However, among sera from Brazilian and Swedish patients, more than 80% revealed sensitisation to this allergen.
Of 80 B. tropicalis-sensitive Taiwanese patients, 4.7% were allergic to Blo t 3. However, in a study of mite-allergic subjects in Singapore, the frequency of IgE reactivity to the recombinant Blot t 3 was 50%; but the IgE titer was generally low. A study in this population, using native Blo t 3 in 44 mite-allergic sera, reported an IgE reactivity frequency of 57% .
Among 80 B. tropicalis-sensitive Taiwanese patients, 7.5% were shown to be allergic to Blo t 4.

Frequencies of sensitisation to Blo t 5 in Taiwanese and Malaysian patients’ sera were shown to be 91.8% and 73.5%, respectively. Other studies have reported Blo t 5 to be a major allergen, with sensitisation rates of up to 70% in populations prone to B. tropicalis allergy. Most patients appear to be concurrently sensitised to D. pteronyssinus, and around 18% of patients may be found to be sensitised to B. tropicalis as a result of cross-reactivity of D. pteronyssinus. In a Colombian study, 24% of mite-allergic patients were shown to have IgE binding to B. tropicalis extract. A study compared the importance of 2 types of sensitisation: to B. tropicalis and D. pteronyssinus among asthma patients from Florida, Puerto Rico, and Brazil; and to D. pteronyssinus among patients from the United States and the United Kingdom. IgE antibodies to recombinant Blo t 5 were found in 45% of sera from B. tropicalis-allergic asthmatics in the group from Florida, Puerto Rico, and Brazil, compared to 69% of similar patients in the United States and United Kingdom group. In vivo and in vitro comparisons of IgE responses to B. tropicalis, D. pteronyssinus, rBlo t 5, and rDer p 5 showed that B. tropicalis has unique allergens that cause allergen-specific IgE responses, suggesting that B. tropicalis is an independent cause of sensitisation.

Blo t 5 is a major allergen of B. tropicalis, with up to 92% of allergic patients sensitised to it. Native Blo t 5 has been purified and shown to consist of multiple isoforms. In a study in Barbados, Blo t 5 sensitivity was present in 46% of 261 subjects and was associated with younger age, higher total serum IgE level, and asthma – the prevalence of asthma in the Blo t 5-sensitive subjects was more than 3-fold greater (42 vs. 13%). Der p 1 sensitivity was less common (27%) but showed similar associations with age, IgE, and asthma. Of the 261 subjects sensitised to Blo t 5, 116 were also sensitised to Der p 1; they were younger, had higher total and Blo t 5-specific IgE levels, and had more than twice the asthma prevalence as those sensitised to Blo t 5 alone (59 vs. 29%). As in other studies, Der p 1 sensitivity without Blo t 5 sensitivity was uncommon; 90% of those sensitised to Der p 1 were also sensitised to Blo t 5.

A study of asthmatics’ homes in Hong Kong concluded that Der p 1 and Blo t 5 were the major allergens found in this region, and that Blo t 5 was a more potent allergen in Hong Kong, probably reflecting the high level of exposure to B. tropicalis.
Sensitisation to Blo t 6 has been reported in 11.1% of 80 B. tropicalis-sensitive Taiwanese patients.
A study using rBlo t 10 demonstrated that up to 96% amino acid identity was shared with tropomyosin of other mites, and skin specific IgE and ELISA IgE immunoassay tests found rBlo t 10 sensitisation rates of between 20% and 29% in atopic subjects. As in the case of other specific Blomia allergens, some allergic individuals had unique IgE epitopes for Blo t 10.
Sensitisation to Blo t 11 has been reported in 10% of 80 B. tropicalis-sensitive Taiwanese patients. A study using rBlo t 11 found sensitisation in 52% of 63 sera from asthmatic patients.
Of 80 B. tropicalis-sensitive Taiwanese patients, 16.3% were allergic to Blo t 12. In a study with Bt6 (Blo t 13), the frequency of IgE binding of allergic sera was generally low (11%) and weak, with the exception of 1 serum which did show strong specific IgE reactivity.
Blo t 21 shares 39% identity with Blo t 5. It is present in the midgut and hindgut contents as well as in faecal particles of B. tropicalis. IgE antibodies to Blo t 21 were detected in 93% (40/43) of B. tropicalis sensitised individuals by means of ELISA and 95% (41/43) by means of skin reactivity in an evaluation of 43 adult patients with ongoing persistent allergic rhinitis. However, sera of 494 consecutive individuals attending outpatient allergy clinics over 18 months showed that 57.9% (286/494) were sensitised to Blo t 21. Although the majority (>75%) of sensitised individuals were co sensitised to both Blo t 5 and Blo t 21, these 2 allergens had a low to moderate degree of cross-reactivity.
A study evaluated the presence of IgE, IgG1, and IgG4 to concanavalin A-binding antigens (Bt-Con-A) isolated from B. tropicalis (Bt)-total extract in sera of 121 patients with allergic rhinitis. Skin reactivity for B. tropicalis was found in 58% of the patients. Proteins of 14-152 kDa were isolated from Bt-total, and components >27 kDa from the Bt-Con-A extract. The authors concluded that Con-A-binding components isolated from B. tropicalis constitute major allergens and are involved in both allergen sensitisation (IgE response) and homeostasis maintenance (IgG1 and IgG4 responses) (40).

IgE-mediated reactions
Several investigations have demonstrated that allergens from B. tropicalis may play an important role in sensitisation and allergic symptoms. Sensitisation to B. tropicalis has been associated with acute asthma that requires emergency room treatment both among children and adults.

B. tropicalis occurs in a significant percentage of homes in tropical and subtropical regions of South America and Asia, as well as in the United States and Europe. In these areas, B. tropicalis has been shown to be a clinically important allergenic component of house dust, inducing IgE antibody response in patients with allergic diseases such as asthma and rhinitis. In a Brazilian study, patients with atopic dermatitis showed a high degree of sensitisation to B. tropicalis, and the authors suggested that exposure to it can thus be considered a risk factor for the development of AD exacerbations.

In a study in Tampa, Florida, subjects with allergic rhinitis were challenged with B. tropicalis extracts. Ten out of 12 (83%) subjects had positive nasal challenge responses to B. tropicalis, as measured by rhinometry. The authors concluded that B. tropicalis should be considered a risk factor for allergic rhinitis when a patient is evaluated who lives in an area where it is endemic.
In studies in Lima, Peru, Cartagena, Colombia, Singapore and Malaysia, B. tropicalis was the mite most frequently detected. A study in Tampa, Florida, identified B. tropicalis in 30% of the dust samples from homes in the area.

In the Canary Islands, in a study of patients who were sensitised to 2 mite species, D. pteronyssinus and B. tropicalis, it was confirmed that individuals may react only to 1 of these, supporting the evidence that, although there is some in vitro and in vivo allergenic cross-reactivity between B. tropicalis and D. pteronyssinus, clinical symptoms induced by the inhalation of B. tropicalis and D. pteronyssinus seem to be species-specific; however, some patients may react to common allergens.

Among Thai patients, skin reactivity to D. pteronyssinus was found in 62.5% of 40 adults and 51.1% of 45 children; and to B. tropicalis in 37.5% and 40%, respectively. In a study in Taiwan and Singapore, although Der p 1, Der p 2 and Blo t5 were found to be major sensitising allergens in both countries, Blo t 5 was found to be a more potent one in Singapore than in Taiwan, probably reflecting the high level of exposure to Blomia in that country. Similarly, in a Taiwanese study of 498 atopic children aged 2 to 16, a high prevalence of sensitisation – 90.2% to D. pteronyssinus, 88.2% to D. farinae, 79.5% to D. microceras, and 76.7% to Blomia tropicalis – was documented.

In a study of 124 individuals with allergic rhinitis in Malaysia and Singapore, it was found that sensitisation to Blo t extract was positive in 73% of 124 individuals, while sensitisation to Blo t 5 was positive in 50%. Among 105 patients without rhinitis, sensitisation to Blo t extract was found in 57%, and to Blo t 5 in 23%. Of Malaysian asthmatic adults, 37% were sensitised to Blo t 5, and of the asthmatic children, 90% were sensitised to Blo t 5. The study clearly demonstrated that dual sensitisation to B. tropicalis and D. pteronyssinus was common in the general populations of Singapore and Malaysia, and that sensitisation to Blo t 5 was more prevalent than to Der p 1 and Der p 2. In a subsequent study of 175 patients with newly diagnosed allergic rhinitis, with a mean age of 7.9 years (range 2-16), 39% reported a concomitant diagnosis and/or clinical complaints of bronchial asthma, and 48% of atopic dermatitis. Skin prick test results were positive for familiar House dust mites (D. pteronyssinus and D. farinae mix) in 85% of patients, and for B. tropicalis in 62%. The authors concluded that in this population, B. tropicalis sensitisation is more prominent in children with pure respiratory allergy.

In Taiwan, 73.3% of asthmatic patients were reported to be sensitised to Blomia. Concurrent sensitisation to both B. tropicalis and D. pteronyssinus occurred in 63.3% of these patients.

A number of studies from South America have demonstrated the importance of Blomia as a sensitising agent on that continent. B. tropicalis sensitisation was shown to occur, among allergic patients, in prevalences ranging from 47% in Mexico City to 93.7% in São Paulo. Even very young children may be sensitised to this allergen, the mean age in São Paulo being 2.9 years. In Caracas the prevalence of sensitisation was 77.8%. In a repeat study in Caracas ten years later, the prevalence had increased to 91.6% for B. tropicalis, and 97.2% for D. pteronyssinus.

A high prevalence of sensitisation to B. tropicalis has also been reported in patients with persistent allergic respiratory symptoms in Venezuela. Skin reactivity in 92.2% of 115 patients was shown to either B. tropicalis or D. pteronyssinus or both; 70.4% were positive to both, 10.4% only to D. pteryonyssinus, and 11.3% only to B. tropicalis. IgE antibodies to either or both were detected in 93%, in 69.6% to both, in 11.3% only to D. pteronyssinus, and in 12.2% only to B. tropicalis. In a second Venezuelan study, 204 allergic patients attending specialised clinics in Caracas were studied. Sensitisation to B. tropicalis was documented in 90.6%. Monosensitisation to B. tropicalis occurred in 2.4%, whereas none reacted exclusively to B. kulagini.

In a Brazilian study, the presence of skin specific IgE to B. tropicalis was found in 61.8% of patients with atopic dermatitis and 83.33% of asthmatic patients, and in 12.5% of the control group. IgE antibodies were present in 44.1% of those with atopic dermatitis and in 61.9% of asthmatic patients, but in none of the control group. Among 110 Brazilian patients with allergic rhinitis with or without asthma, 56% had skin reactivity to B. tropicalis, 51% to both B. tropicalis and D. pteronyssinus, and 6% to B. tropicalis only. IgE antibodies for B. tropicalis were found in 43% of these patients.

In Brazil, nasal challenges with B. tropicalis in a group of sensitised patients were positive in 60% of cases (and 90% had positive challenges to D. pteronyssinus). In Singapore, positive nasal challenges to B. tropicalis were demonstrated; it was also shown that B. tropicalis may provoke a concomitant asthmatic response during the late-phase reaction. A clinical study was recently made of patients with allergic respiratory disease who attended an allergy clinic in Brazil. Of 212 medical records evaluated, 61.7% were of patients sensitised to Der p, 59.9% to Der f and 54.7% to B. tropicalis. The high prevalence of sensitisation is not surprising, considering the high level of B. tropicalis infestation of dwellings. In an investigation of mites and the presence of Blo t 5 on beds used by individuals with different socioeconomic backgrounds in Salvador, a major Brazilian city, 89% of the beds analyzed were found to harbour at least 1 mite species. B. tropicalis was found in 71.8% and D. pteronyssinus in 39.9%. B. tropicalis was found with a similar frequency in beds of both socioeconomic groups, whereas D. pteronyssinus was found more frequently in the beds of the wealthy than of the poor group .

In Valdivia, Chile, among 100 consecutive asthmatic paediatric patients evaluated, 80 were confirmed to have skin specific IgE to at least 1 mite species. Sixty patients had asthma and allergic rhinitis, 12 asthma and eczema, and 8 asthma, allergic rhinitis and eczema. All patients with skin reactivity for mites were positive to D. pteronyssinus, 99% to D. farinae, 92% to Euroglyphus maynei, 80% to Lepidoglyphus destructor, 73% to Tyrophagus putrescientae, 72% to B. tropicalis, 70% to Acarus siro and 68% to Chortoglyphus arcuatus. All of the patients with severe persistent asthma, 85% of those in the moderate group, and 73% of those in the mild group had skin reactivity to mites. Ninety-five percent of patients with asthma and allergic rhinitis were shown to have skin reactivity to mites, along with 92% of patients with asthma and eczema and 100% of patients with asthma, allergic rhinitis and eczema.

D. pteronyssinus, D. siboney and B. tropicalis have also been reported to be the most important allergenic mites in Cuba. A total of 88.4% of patients were positive to D. siboney, 87.1% to D. pteronyssinus, and 68.1% to B. tropicalis. Sensitisation to Dermatophagoides species was predominant, as demonstrated by the fact that 31.9% of patients showed positive SPT to either D. siboney or D. pteronyssinus only, whereas only 5.6% was sensitised solely to B. tropicalis. Nevertheless, most patients (58.6%) were polysensitised to the 3 species.

Although a very high rate of sensitisation to B. tropicalis has been found in atopic individuals in tropical and subtropical environments, studies have reported high prevalences of sensitisation in countries with temperate climates; the species Blomia tjibodas, B. kulagini, and B. thori appear to partake of this phenomenon.

In Germany, a high rate of IgE antibodies to B. tjibodas and B. tropicalis in allergic city dwellers and farmers was reported. In a study of B. tropicalis-sensitive patients in Florida, 83% had a positive nasal challenge with B. tropicalis extract, suggesting that the presence of IgE antibodies to this mite is a good predictor of allergic symptoms due to inhalation of allergens from the mite.

Other reactions Occupational allergy to Blomia kulagini present on cheese rind has been reported.
Systemic anaphylaxis can occur after the ingestion of heated or unheated mite contaminated foods. This problem may be more prevalent in tropical and subtropical countries than previously recognised. The most common symptoms following the ingestion of mite-contaminated flour were breathlessness, angioedema, wheezing, and rhinorrhoea, and these started between 10 and 240 minutes after eating.