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|Route of Exposure||Inhalation|
|Source Material||Whole body culture|
|Latin Name||Dermatophagoides farinae|
|Other Names||House dust mite, Dust mite|
House dust mites (HDMs) are the most important causes of allergic sensitization and allergic disease, including Dermatophagoides farinae as one of the principal species. Mites dominate in environments with temperate climates, damp, and humid dwellings. The HDM fecal pellets are reported to be the major source of allergens causing allergic reactions after inhalation. Mite allergens can trigger the symptoms in a sensitized individual through inhalation, ingestion and direct contact. Out of all the D. farinae allergens listed, Der f 1, Der f 2, Der f 11 and Der f 23 are the major allergens. A high degree of cross-reactivity is noted between D. pteronyssinus and D. farinae extracts, whereas the reactivity between Dermatophagoides and Blomia tropicalis is limited. Furthermore, a high degree of cross-reactivity is also observed between Der p 1 and Der f 1, Der p 2 and Der f 2, and between Der f 23 and Der p 23. Tropomyosins play an important role in the cross-reactivity. It has been reported that tropomyosin allergens from HDMs cross-react with crustaceans (shrimp, lobster, crab, crayfish) and mollusks (mussel, oyster, scallop, clams, abalone, snails, squid, octopus, cuttlefish). Furthermore, Der f 10 is found to be cross-reactive with Blo t 10, Lep d 10, Pen a 1, Per a 7 and Hom a 1.
Globally, house dust mites (HDMs) are the most important causes of allergic sensitization and allergic diseases. The HDMs are reported to colonize to the indoor environment, and the allergens of HDM target the epithelium of humans, thus demonstrating the unique characteristics of HDMs (1).
The most important HDM species are Dermatophagoides farinae (D. farinae), Dermatophagoides pteronyssinus (D. pteronyssinus) and Euroglyphus maynei (E. maynei). The characteristics of D. farinae co-exists with that of the storage mite, Blomia tropicalis (B. tropicalis), found in the subtropical and tropical areas, as a major source of mite allergen (1, 2).
D. farinae produces one or two eggs in a day, however, it can sometimes even lay 5 or 6 eggs per day (3). The adult mites have nonsegmental bodies that measure between 250 to 350 μm in length. The HDMs move on 8 legs and possess hair-like structure on their entire body, that functions as feelers. Further, the suction cup-like feature on their feet help the mites to stick to the surfaces (1).
House dust mites are most prevalent in the indoor environment of every household, located in the temperate areas. It is reported that mites survive the dry winters with humid, temperate climates. High allergen levels of mites are reported in older homes, and in homes that are devoid of air-conditioning, as compared to those with air-conditioners (1). The longevity of D. farinae male and female species differ, with the duration of survival between 18 to 64 days in males and 20 to 54 days in females (1, 3). Furthermore, the female species achieve its complete cycle of egg to adult in 35 days, when the optimum temperature is between 23-30°C (1, 3). However, the time duration of their survival might increase, with an increase in the temperature and humidity in environment (1).
|Taxonomic tree of D.farinae (1,4)|
Mites, including D. farinae, during its lifespan produces ~1000 solid wastes, each measuring about 25 µ diameter (1). The fecal pellets of HDM (including D. farinae) are reported to be the major source of allergen carrier in air, causing allergic reactions after inhalation (1, 5). Further, the pellets become transiently airborne during disturbance brought about by human activities, such as sweeping, dusting, vacuuming, or changing bedding (2).
Generally, high altitudes are not favorable place for dust mites to live in, and hence it is important to know that, even before the dust mites were discovered, sanitaria were frequently built for patients with respiratory diseases, e.g., in the Alps (Europe) and Denver, CO (USA) (1). Low sensitization and growth of dust mites have been observed in the Alps than at sea level, due to the lower indoor humidity observed at high altitudes (6, 7). However, contrasting results were obtained in a study conducted at high altitudes in a tropical developing country. According to this cross-sectional study, 87.9% of asthmatic children were found positive to at least one HDM type (n=61). Further, out of the sensitized children, 70.7% showed sensitivity to D. farinae (8).
According to a systematic analysis conducted on 163 articles, involving 114,302 allergic cases in China, the rate of D. farinae sensitization was reported to be 75.2% in patients with allergic rhinitis (AR), whereas it was 78.5% in patients with allergic asthma (9).
Dust mites are found worldwide, except in the Arctic and Antarctic (1). Mites dominate in the environment, that has temperate climate, with damp and humid dwellings. Countries with such environment, include Scotland, Europe (West and Central), New Zealand, Australia, England, areas of United States and South America, where homes are both warm and damp. In contrast, in northern region of Europe, where the climate is extremely cold and dry, the mites cannot survive the weather (5).
The species of Dermatophagoides are found throughout the world, including the United States, South America, Hawaii, the Middle East, Canada, Europe, Asia, parts of Australia, and Africa. D. farinae are most commonly found in the United States, whereas in United Kingdom, it is less commonly seen (3).
Airway inhalation is the primary route of exposure to HDM. It has been reported that post-inhalation of a dust mite allergen, reduction in mucociliary clearance is observed, which in turn is found to escalate the deposition of inhaled particles (10). Further, it has been found that exposure of HDM allergen can act as a trigger in exacerbating the existing condition of asthma (1).
Mite allergens can trigger the allergic symptoms in a sensitized person through various routes, including inhalation (asthma, AR, eczema), ingestion (anaphylaxis, urticaria), and direct contact (conjunctivitis, eczema) (1).
Mite-allergic patients with asthma might also have symptoms of AR. This supports the “unified airway” concept that asthma and AR may not be separate entities, but rather linked manifestations of allergic inflammation, occurring throughout the upper and lower airways (11).
According to a 13-month, multicenter survey, severe or very severe burden of AR and asthma, caused by HDM was noted in terms of irritability, tiredness, disturbed sleep, and troublesome professional life (12).
According to a study conducted in China (Qingdao region), D. farinae was responsible for causing AR in 66.4% of children (1887 out of 2841 children). It was reported that sensitization to HDM was more in older children with AR, particularly the males. Clinical manifestations of AR are likely to have an effect on studies, work productivity and efficiency, as well as the quality of life (13).
Many patients are unaware that dust mites are a trigger for their asthma, yet report symptoms of sneezing, wheezing or eye irritation while performing their activities, such as house cleaning, or upon waking up (5).
Exposure to HDM during early childhood elevates immunoglobulin E (IgE) levels, which in turn predisposes to asthma. Mite allergy is a major risk factor for asthma, and sensitization to mites, early in life has a significant impact on pulmonary function (14).
A study was conducted in 2087 allergic patients, out of which, 82% of patients demonstrated a positive skin prick test (SPT) for HDM allergens. D. farinae was one of the predominant species, with a prevalence of 61%. The dust allergen load (>10 µg/g) was notably higher in Der f 1 (57.6%) than Der p 1 (20%), thus indicating as a risk factor for the development of asthma (15).
In a cross-sectional study, 31% of severely asthmatic children were found to have an obstruction (forced expiratory volume in one second/forced vital capacity [FEV1/FVC] <80%). A significant correlation (Rho: −0.34; CI 95%: −0.55 to −0.09; P=0.008) was observed between FEV1/FVC and positive SPT, indicating the presence of obstruction. Further, it has been observed that an elevated risk of progressive lung function loss could be noted in children with asthma, atopy, and reduced pulmonary function (8).
The prevalence of sensitization to mites can be very high in patients with atopic dermatitis (AD). The increase in the permeability of atopic skin and the ability of mite proteases to decrease skin barrier function may allow more effective sensitization with aeroallergens, initiating a vicious cycle of inflammation and further allergen exposure (1).
A retrospective, cohort study was conducted on 102 children with AD (median age at onset: 1.5 years). Children were majorly sensitized to HDMs, including D. farinae and D. pteronyssinus, across all the age groups (<2 years, between 2-7 years and >7 years), however, sensitization to HDMs was higher in children >7 years of age (16).
Unintentional ingestion of dust mites in the form of food (contaminated with mites), can cause systemic allergic symptoms (1). In a case of a 48-year-old male, ingestion of fried pastry, prepared from flour contaminated with D. farinae, led to anaphylaxis (1, 17).
According to evidence, sublingual immunotherapy (SLIT) could be considered as a safe and effective route of administration. In a retrospective study conducted among 282 children with AR in China, SLIT with D. farinae drops was found to be safe and efficacious in pre-school and school-age children with AR, induced by HDMs (18).
The exposure of HDMs can be prevented or reduced by wrapping the mattresses, pillows, and box springs in coverings, that are allergen-proof, washing the bedding with hot water in a week, cleaning the house, wearing an appropriate mask while cleaning, changing furnace and air-conditioner filters, and using a dehumidifier, that help in decreasing the humidity in homes (2).
In a study conducted in Malaysia, use of commercial ionizer was found to be successful as well as effective in increasing the mortalities in mites (including D. farinae and D. pteronyssinus) by increasing the length of exposure time of ionizer. It has been reported that production of negative ions by the ionizer had the capability of killing the HDMs and further decreasing the population of natural mites on surfaces, such as clothes, mattresses, floors, curtains, etc. (19).
In mite-sensitized asthmatic patients, bronchial hyperreactivity and bronchospasm was found to be aggravated, upon exposure to mites, however, the symptoms got improved in mite-free environment (1). Decreased exposure to mites in patients with mite allergy can be an effective tool in managing allergic patients, such as asthma (20).
The recognition of HDM-specific allergens helps in the diagnosis and treatment of allergic diseases, associated with HDM, especially identification and characterization of novel HDM allergens (21). The allergens of D. farinae listed in the WHO/IUIS database include (22).
|Allergen||Biochemical name||Molecular Weight (kDa)||Allergenicity|
|Der f 1||Cysteine protease||27||
|Der f 2||NPC2 family||15||
|Der f 3||Trypsin||29|
|Der f 4||Alpha-amylase||57.9|
|Der f 5||Low molecular weight IgE binding protein||15.5|
|Der f 6||Chymotrypsin||25|
|Der f 7||Bactericidal permeability-increasing like protein||30-31|
|Der f 8||Glutathione S-transferase||32|
|Der f 10||Tropomyosin||37||
|Der f 11||Paramyosin||98||
|Der f 13||Fatty acid binding protein||15|
|Der f 14||Apolipophorin||177|
|Der f 15||Chitinase||98/109|
|Der f 16||Gelsolin/villin||53|
|Der f 17||Calcium-binding protein||53|
|Der f 18||Chitin-binding protein||60|
|Der f 20||Arginine kinase||40|
|Der f 21||Not determined||14|
|Der f 22||Not determined||14.7|
|Der f 23||Peritrophin-like protein||19||
|Der f 24||Ubiquinol-cytochrome c reductase binding protein homologue||13|
|Der f 25||Triosephosphate isomerase||34|
|Der f 26||Myosin alkali light chain||18|
|Der f 27||Serpin||48|
|Der f 28||Heat Shock Protein||70|
|Der f 29||Peptidyl-prolyl cis-trans isomerase (cyclophilin)||15|
|Der f 30||Ferritin||15|
|Der f 31||Cofilin||15|
|Der f 32||Secreted inorganic pyrophosphatase||35|
|Der f 33||Alpha-tubulin||52|
|Der f 34||Enamine/imine deaminase||16|
|Der f 35||Not determined||14.4|
|Der f 36||Not determined||23|
|Der f 37||Chitin binding protein||29|
|Der f 38||Bacteriolytic enzyme||15|
|Der f 39||Troponin C||18|
Der f: Dermatophagoides farinae; IgE: Immunoglobulin E; RAST: Radioallergosorbent; ELISA: Enzyme-linked immunosorbent assay; SPT; Skin prick test.
The prevalence of IgE reactivity was observed to be 94.7%, of the total HDM extract, in a study conducted on 129 HDM-allergic Korean patients. It was reported that 79.1% of patients showed specific IgE to Der f 1 and Der f 2. Further, 9.3%, 6.2%, 7%, and 7% of patients showed IgE reactivities to Der f 6, Der f 8, Der f 10, and Der f 20, respectively. In HDM-allergic patients having respiratory allergy and AD, Der f 2 was the most sensitized allergen. Further, the diagnostic sensitivity was reported to be increased with the combination of the group 1 (Der f 1) and 2 (Der f 2) major allergens (28).
Apart from the WHO/IUIS list, another allergen of D. farinae, Der f Alt a 10 has been described by a study. According to the findings reported in this study, 32.7% of AD patients were sensitized to Der f Alt a 10, in comparison to 3.0% in patients with allergic asthma/AR (29).
The allergic sensitivity, following the ingestion of HDMs, show symptoms in two different forms - the ingestion of invertebrates demonstrating cross-reactivity with mite allergens, and the ingestion of foods that are contaminated with dust mites (1).A high degree of cross-reactivity is noted between D. pteronyssinus and D. farinae extracts, however, the reactivity between Dermatophagoides and B. tropicalis has been reported to be low (5).
According to a study, co-sensitization and cross-reactivity has been reported between B. tropicalis and two Dermatophagoides species, i.e., Der p and Der f. In this study, 70.14% of allergenic patients (1050 out of 1497 patients) were found to be co‐sensitized to B. tropicalis, Der p, and Der f. However, the cross-reactivity between B. tropicalis and Dermatophagoides was limited (30).
The structural similarities between Der p 1 and Der f 1 was demonstrated with an X-ray crystal structure analysis. The analysis showed a surface conservation of a crystal structure of natural Der f 1 with Der p 1, having 71% of amino acid similarity, along with an overlapping catalytic area. This high structural similarity observed between Der p 1 and Der f 1 are commonly believed to be the basis for their cross-reactivity (31, 32).
A high degree of cross-reactivity has also been reported between Der p 2 and Der f 2 (from D. farinae) (33).
Group 11 allergens (Der p 11, Der f 11) are considered as major allergen molecules in patients with AD, having sensitization to HDM, and thus should be included among allergen components for the routine testing in the clinical laboratory (34).
A high amino acid sequence similarity has been found between Der p 23 and Der f 23 (87%). Different structural studies of Der p 23 and consecutive modelling of Der f 23 on its structure, might imply on the occurrence of considerable cross-reactivity between the two proteins (35).
Der f 10 (tropomyosin from Der f) and Der p 10 of HDM, both are found be cross-reactive with Lep d 10 (tropomyosin from the storage mites), due to high level of homology (36).
Tropomyosins are a large family of heat-resistant, alpha-helical proteins. These proteins form a coiled-coil structure of two parallel helices, that includes two sets of seven alternating actin-binding sites. This feature plays a vital role in regulating the function of actin filaments (37).
One of the most important cause of cross-reactivity, among mites, shellfish, helminths, and cockroaches is the Tropomyosin, although glutathione transferase may also be included. In cases where genuine sensitization is unclear, specific allergen components can be useful to identify primary allergy (5).
Tropomyosin allergens from HDMs are reported to show cross-reactivity with tropomyosin allergens of invertebrates, such as crustaceans (shrimp, lobster, crab, crayfish), mollusks (mussel, oyster, scallop, clams, abalone, snails, squid, octopus, cuttlefish) and insects (cockroaches) (1, 37).
Der f 10 allergen has shown sequence similarity with shrimp tropomyosin Pen a 1, American cockroach tropomyosin Per a 7, and lobster tropomyosin Hom a 1 (38).
Further, cross-reactivity has been reported between HDM and shrimp-reactive IgE antibodies, in patients with shrimp allergy (39). In patients with allergy to HDMs, reactivity to shrimp has also been revealed, especially in patients who were never been exposed to shrimps, because of religious dietary habits (40).
Author: Turacoz Healthcare Solutions
Reviewer: Dr. Christian Fischer
Last reviewed: January 2021