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PubMed2002

Virulence and site of infection of the fungus, Hirsutella thompsonii, to the honey bee ectoparasitic mite, Varroa destructor.

The Varroa mite, Varroa destructor, is recognized as the most serious pest of both managed and feral Western honey bee (Apis mellifera) in the world. The mite has developed resistance to fluvalinate, an acaricide used to control it in beehives, and fluvalinate residues have been found in the beeswax, necessitating an urgent need to find alternative control measures to suppress this pest. Accordingly, we investigated the possibility of using the fungus, Hirsutella thompsonii, as a biocontrol agent of the Varroa mite. Among the 9 isolates of H. thompsonii obtained from the University of Florida and the USDA, only the 3 USDA isolates (ARSEF 257, 1947 and 3323) were infectious to the Varroa mite in laboratory tests. The mite became infected when it was allowed to walk on a sporulating H. thompsonii culture for 5 min. Scanning electron micrographs revealed that the membranous arolium of the mite leg sucker is the focus of infection where the fungal conidia adhered and germinated. The infected mites died from mycosis, with the lethal times to kill 50% (LT(50)s) dependent on the fungal isolates. Thus, the LT(50)s were 52.7, 77.2, and 96.7h for isolates 3323, 257, and 1947, respectively. Passage of H. thompsonii through Varroa mite three times significantly reduced the LT(50)s of isolates 257 and 1947 (P<0.05) but not the LT(50) of isolate 3323. The fungus did not infect the honey bee in larval, prepupal, pupal, and adult stages under our laboratory rearing conditions. Our encouraging results suggest that some isolates of H. thompsonii have the potential to be developed as a biocontrol agent for V. destructor. However, fungal infectivity against the mites under beehive conditions needs to be studied before any conclusion can be made.

Animals↗
PubMed1998

Multiple sclerosis with mite antigen-specific IgE.

The total and mite antigen-specific IgE in the sera were measured in 60 patients with multiple sclerosis (MS) and 40 healthy controls by an enzyme-linked immunosorbent assay using two common mite antigens, Dermatophagoides farinae and Dermatophagoides pteronyssinus, in order to study the role of atopy in MS. Neither the total IgE level nor the frequency of mite antigen-specific IgE differed significantly between the MS patients (mean total IgE 162 U/ml, 42% mite IgE-positive) and healthy controls (mean total IgE 168 U/ml, 35% mite IgE-positive). The MS patients with mite antigen-specific IgE showed a significantly higher level of serum total IgE (mean 293 U/ml, P=0.0005) and a higher frequency of atopic disorders (36%, P=0.0508) than did the MS patients without mite antigen-specific IgE (mean total IgE 68 U/ml, atopic disorders 14%). The former group also showed a significantly higher frequency of male (P=0.0216), a younger age of onset (P=0.0081), a lower expanded disability status scale (EDSS) score (P=0.03) and a lower protein content in the cerebrospinal fluid (CSF) (P=0.0426) than the latter, while the duration of disease and a number of relapses did not differ significantly between the two groups. In addition, the mite IgE-positive MS showed a very low frequency of oligoclonal IgG bands in CSF (4%) and a significantly higher association of HLA-A24 (87.5%) than the healthy controls (45%). Therefore, the presence of IgE response to the mite antigens and atopy appeared to significantly lessen the severity of the disease and the immunologic abnormalities in MS.

Adult↗
PubMed1995

Chemical treatment of carpets to reduce allergen: comparison of the effects of tannic acid and other treatments on proteins derived from dust mites and cats.

BACKGROUND: Several chemical treatments have been recommended for reducing mite and other allergen levels in carpets, including the protein-denaturing agent tannic acid (TA). OBJECTIVE: We evaluated the efficacy of TA and other treatments on mite and cat allergens in carpets within houses. The effects of TA were assessed on Der p 1 and Der f 1, on group II mite allergens, and on the major cat allergen Fel d 1. METHOD: Carpet treatments tested were benzyl benzoate moist powder, a 3% TA spray, and two carpet cleaners (Host and Capture). Carpets were treated twice and dust samples collected on a biweekly basis for 8 weeks: these samples were extracted in saline solution alone. Additional studies evaluated the effects of TA on 17 carpets. Carpets were treated twice (on days 0 and 28) and samples collected on days 0, 1, 7, 14, 28, and 42. Eighteen carpets were untreated controls. Dust samples were extracted separately in both saline solution and in the presence of 5% bovine serum albumin. RESULTS: Benzyl benzoate and the two carpet cleaners reduced group 1 dust mite allergen concentrations in carpet dust. In addition, benzyl benzoate and TA reduced airborne group 1 mite allergens by more than 64%. Further studies showed that, in keeping with in vitro studies, TA inhibited the assay and bovine serum albumin abrogated this effect. Significant reductions after treatment occurred only for Der f 1 and group 2 dust mite allergens (p = 0.005 and p = 0.035, respectively). However, for all mite allergens the percentage changes after treatment were significant when compared with untreated carpets (p < 0.005 for Der f 1 and group 2 mite, p < 0.02 for Der p 1) but not for cat allergen (p > 0.3). The results suggested that repeated application of TA was necessary to maintain reduced allergen concentrations. CONCLUSION: Carpet treatments can reduce mite-derived allergen levels in airborne and carpet dust. However, the effects do not appear to be maintained for long periods, are not dramatic, and are different for different allergens.

Allergens↗
PubMed2005

Systemic anaphylaxis after the ingestion of pancake contaminated with the storage mite Blomia freemani.

BACKGROUND: Systemic anaphylaxis after the ingestion of mite-contaminated food has rarely been reported. OBJECTIVE: To describe an 8-year-old boy in whom systemic anaphylaxis developed shortly after the ingestion of pancakes prepared with commercial pancake flour. METHODS: The patient underwent skin prick testing for house dust mites and with uncontaminated and mite-contaminated pancake flour. Specific IgE for mites and the main ingredients of the pancake flour were also evaluated, with titers for Der p 1, Der f 1, and Blo t 5 quantitated using immunochemical methods. A sample of pancake flour was examined microscopically for mites. RESULTS: The patient had positive skin prick test results to contaminated pancake flour extract (1 g/5 mL), Dermatophagoides pteronyssinus, and Dermatophagoides farinae but a negative skin test response to uncontaminated pancake flour. The patient's serum specific IgE analysis was positive for antibodies to dust and storage mite allergens. There was no response, however, to the main ingredients of the pancake mix. Microscopic examination of the pancake flour revealed the storage mite Blomia freemani. Using an immunochemical assay, we found that the contaminated flour contained 5.4 microg/g of the allergen Blo t 5 but no Der p 1 or Der f 1. CONCLUSIONS: This patient's anaphylactic episode was the result of ingestion of the storage mite B. freemani. To our knowledge, this is the first reported systemic hypersensitivity reaction caused by this mite anywhere in the world.

Allergens↗
PubMed2000

Gall mite molecular phylogeny and its relationship to the evolution of plant host specificity.

The phylogenetic relationships of all seven known species of Cecidophyopsis mites (Acari: Eriophyidae) with Ribes hosts have been inferred from ribosomal DNA sequences. This analysis found groups of closely related mites. The five gall-forming species, four of which are monophagous and one which has two hosts, were found in two groups. Another group consisted of the two non gall-forming species, one of which has two hosts, while the other is monophagous. The molecular phylogeny of their known Ribes host plants was calculated using the equivalent ribosomal regions as the mites. The structure of the two trees (mites vs hosts) was clearly different, implying that mite speciation did not closely follow speciation events in the plant hosts. Instead, the three groups of Ribes-infesting Cecidophyopsis mites have derived from a common galling ancestor millions of years ago. Each mite group has recently diversified onto different primary hosts. One group of mites has also lost the galling habit. The results have implications for host range changes and the durability of mite-resistance genes in cultivated Ribes.

Animals↗
PubMed2003

Adaptive learning in arthropods: spider mites learn to distinguish food quality.

Many herbivorous arthropods have been shown to possess learning capabilities, yet fitness effects of learning are largely unknown. In this paper, we test whether two-spotted spider mites (Tetranychus urticae) learn to distinguish food quality in choice tests, and whether this results in fitness benefits. Food consisted of cucumber plants with one of three degrees of feeding damage: undamaged (no mites), mildly damaged (infested by a mite strain adapted to tomato) and heavily damaged (infested by a mite strain adapted to cucumber). Mites were subjected to one choice test in a greenhouse and three sequential choice tests on leaf disks. Thereafter, individual mite performance was measured as oviposition rate over four days. In the course of the three small-scale choice tests, preference shifted towards less damaged food. The performance tests showed that learning was adaptive: mites learned to prefer the food type that yielded the higher oviposition rate. Interestingly, innate preferences in the greenhouse tests were close to those shown after learning in the small-scale tests. Given that both strains of mites had not experienced cucumber for several years, we hypothesize that the preference in the greenhouse was due to avoidance of mite odours rather than odours of damaged plants. Through its effect on foraging behaviour, adaptive learning may promote the evolution of host plant specialization in herbivorous arthropods.

Adaptation, Physiological↗
PubMed2004

A new method for mite extraction from leaf samples.

Debris often hampers the detection of mites in washed leaf samples. We describe in detail a method for the extraction of mites from leaf samples, based on the adherence of mite cuticles to liquid paraffin, at the interface of paraffin and ethanol in a so-called mite-counting channel. We demonstrate its efficacy by comparing the mite numbers in samples before and after extraction. We illustrate the method's reliability by extracting known numbers of a taxonomic variety of plant-inhabiting mites, manually added to mite-free debris: for 13 of the 15 taxa all mites were retrieved. This method can also be used to extract small non-mite arthropods such as scales, whiteflies, thrips, cicadellids, hymenopteran parasitoids and psyllids.

Animals↗
PubMed2004

Tactic responses of the parasitic mite, Psoroptes ovis, to light and temperature.

The astigmatid mite, Psoroptes ovis (Hering) (Acari: Psoroptidae), is an obligate, non-burrowing ectoparasite of vertebrates, of particular economic importance in domestic sheep flocks where it causes clinical psoroptic mange. To help understand the behaviour which facilitates transmission via the environment, the responses of P. ovis derived from rabbits (syn. Psoroptes cuniculi) to temperature and light were examined in the laboratory. On a vertical surface of uniform temperature, the presence and direction of illumination had a significant effect on the distance and direction moved by the mites. In darkness or with illumination from both above and below, the mites moved relatively little, but this movement was upwards. In contrast, with illumination from above only, mites moved downwards. When the direction of the illumination was reversed so that it came from below only, the mites moved upwards. On a vertical surface with a temperature gradient, in darkness or with illumination from both above and below, the mites moved up or down towards the area of highest temperature, depending on whether this was above or below, respectively. However, the movement of the mites in response to the temperature gradient was strongly displaced up or down by the presence of unidirectional illumination from above or below, respectively. The results indicate that the movement of these mites is strongly directed towards areas of high temperature but away from higher light intensity. These behaviours might be expected to maintain the position of the mites on a host animal and help them locate the skin surface of a new host when displaced into the environment.

Animals↗
PubMed1999

Sensitization to local dust-mite fauna in Singapore.

BACKGROUND: Recent studies showed the presence of a unique dust-mite fauna in the indoor environment of Singapore. Immediate hypersensitivity to these dust mites, along with other known indoor allergens, may play a role in the pathogenesis of allergic respiratory diseases. This study evaluated the sensitization rates of the local atopic population to these allergens. METHODS: The skin prick test was performed on a total of 391 individuals (289 patients with asthma and/or allergic rhinitis and 102 healthy controls) using extracts of six species of local dust mites (Austroglycyphagus malaysiensis, Blomia tropicalis, Dermatophagoides pteronyssinus, D. farinae, Sturnophagoides brasiliensis, and Tyrophagus putrescentiae) and 10 other common indoor allergens. Total serum IgE and specific IgE to these dust mites were also quantified with the fluorescence allergosorbent test (FAST). RESULTS: The sensitization rates among patients with asthma and/or allergic rhinitis to dust mites and other inhalant allergens tested (via skin prick tests) were as follow: B. tropicalis (96.2%), D. pteronyssinus (93.4%), D. farinae (92.3%), A. malaysiensis (78.2%), S. brasiliensis (71.6%), T. putrescentiae (71.3%), canary feathers (69.9%), Periplaneta americana (cockroach) (59.5%), Blattella germanica (cockroach) (56.4%), mosquito (Aedes sp.) (46.4%), dog epithelia (mixed breed) (34.3%), kapok seed (31.8%), cat hair (29.1%), Aspergillus fumigatus (20.8%), Penicillium notatum (18.0%), and Candida (Monilia) albicans (9.3%). All patients were observed to react to at least three of the six dust-mite extracts, with 254/289 (87.9%) reacting to at least five or to all six. Skin prick responses to the dust mites were found to correlate with the corresponding specific IgE levels quantified by FAST (P<0.001). In addition, specific IgE levels to D. pteronyssinus and D. farinae were highly correlated (Spearman's rank coefficient = 0.76, P<0.001), as were those to B. tropicalis and A. malaysiensis (r = 0.60, P<0.001). CONCLUSIONS: Asthma and/or allergic rhinitis patients were highly sensitized to the local dust-mite fauna. Thus, these dust mites should be considered important allergenic sources of this region.

Adolescent↗
PubMed1991

[Sensitization against storage mites in allergic rhinopathy].

In the past 15 years, storage mites became more common as an agent in allergic airway disease. Sensitization to storage mites has been reported in farmers and grain workers. There were some studies investigating local populations, especially in the north of Europe. The sensitization to storage mites in a rural population seems to be similar to the rate found for Dermatophagoides. The main diseases caused by storage mites are allergic rhinitis and asthma. Although there is a cross-reactivity between Dermatophagoides pteronyssinus and storage mites, most of the antigens were distinct from house dust mite antigens. In our study, we analysed sera obtained from patients with known house dust mite allergy. Patients with a RAST class 2, 3 or 4 for Dermatophagoides pteronyssinus were tested for specific IgE-antibodies against storage mites. The test was performed using the Melja EAST-technique. We obtained a sensibilization rate of 7% for Acarus siro (d70), 17% for Lepidoglyphus destructor (d71), 3% for Tyrophagus putrescentiae (d72) and 13% for Glycyphagus domesticus (d73). According to our results we can conclude that storage mites are relevant allergens in allergic rhinitis, especially in the rural population in Bavaria. Therefore, routine testing in patients with perennial rhinitis is proposed.

Agricultural Workers' Diseases↗
PubMed2001

Allergens of wild house dust mites: environmental Der p 1 and Der p 2 sequence polymorphisms.

BACKGROUND: Sequence diversity is a common feature of mite allergens. Previous studies, using predominantly commercial mite clones, have described several polymorphic residues for Der p 1 and Der p 2. OBJECTIVE: This study aimed at determining the occurrence of sequence diversity in environmental mite isolates. METHODS: Mites were isolated from houses in Perth and Sydney, Australia. Total RNA was extracted from 1 to 30 Perth mites, and cDNA was synthesized by reverse transcriptase PCR. Der p 1 and Der p 2 cDNAs were PCR amplified and sequenced. Genomic Der p 1 DNA was amplified from whole Sydney mites directly by PCR and then sequenced. RESULTS: Twelve Der p 1 and 9 Der p 2 cDNA clones and 3 Der p 1 genomic DNA were analyzed and showed a high frequency of amino acid polymorphisms. Der p 2 displayed a clear pattern of divergence toward 2 alleles that differed by 4 amino acids and had characteristic silent nucleotide changes. The pattern for Der p 1 was different and unusual, with almost no silent nucleotide substitutions but frequent sporadic missense changes. Proliferative responses of peripheral blood mononuclear cells to peptides containing polymorphic residues of Der p 1 were detected in 8 of 19 subjects, with stimulation being found only for either one of the variant forms of the peptides. However, the responses to variants of whole recombinant allergens were similar, as shown for 4 variants of Der p 2. CONCLUSION: Two clones for each of the allergens were identified as containing sequences that were largely representative of environmental isolates. A small-scale reverse transcriptase PCR used to produce cDNA from individual mites isolated from house dust will have wide application for studies on mite genetics and the production of recombinant mite allergens. Differences in T-cell responses to peptides representing variant epitopes were found, but responses to variants of whole recombinant allergens were similar. The GenBank and Swiss Prot database entries for Der p 1 (U11695) and Der p 2 (P49278) have been updated with the inclusion of the sequence polymorphisms described in this study.

Animals↗
PubMed2003

Identification, characterization, and cloning of a complementary DNA encoding a 60-kd house dust mite allergen (Der f 18) for human beings and dogs.

BACKGROUND: House dust mites of the Dermatophagoides genus are the most important cause of perennial allergic disease in both humans and companion animals. Although the major mite allergens for humans are proteins of relatively low molecular weight, this is not the case for dogs. Western blotting shows that canine anti-mite IgE responses are directed primarily toward proteins in the molecular weight range of 50 to 120 kd. OBJECTIVE: The objectives of this study were to characterize a D farinae allergen with a molecular weight of approximately 60 kd and to isolate the cDNA coding for this allergen. METHODS: A protein of apparent molecular weight of 60 kd was identified by Western blotting by using canine serum IgE from house dust mite-sensitized atopic dogs. The protein was purified from homogenized D farinae mite bodies by ammonium sulfate precipitation, followed by gel filtration and cation exchange HPLC. The presence of IgE directed to the 60-kd protein in sera from humans and dogs with dust mite allergy was measured by FcepsilonRIalpha-based ELISA. A cDNA encoding a full-length 60-kd protein was isolated from a D farinae cDNA library by a combination of both PCR amplification and hybridization screening. A panel of mAbs specific for the 60-kd protein was generated and used to localize the protein in whole body sections of D farinae mites. RESULTS: ELISA showed that the purified protein bound IgE in 54% of the sera from patients with D farinae allergy. In addition, the 60-kd protein was able to bind IgE in 57% to 77% of D farinae -sensitized dogs. A cDNA was isolated that encoded a protein of 462 amino acids, consisting of a 25 amino acid signal sequence and a 437 amino acid mature protein. The calculated molecular weight of the mature protein is 50 kd, and the amino acid sequence contains a single N-glycosylation site. A protein database search showed homology with multiple chitinases. A mAb specific for the 60-kd chitinase recognized the allergen in the mite digestive system, but fecal pellets did not stain positively for this allergen. CONCLUSIONS: A 60-kd D farinae protein (Der f 18), with homology to chitinase, is a major allergen for humans and dogs sensitive to house dust mites.

Allergens↗
PubMed1995

Dust mite allergens in the office environment.

The objective of this study was to evaluate the extent of dust mite infestation and its contribution to the health complaints in office settings. The methodology recommended for residential dwellings was evaluated for use in the work environment. Der p I allergen-specific ELISA was chosen as a primary method. A liquid chromatography method for guanine is suggested as a backup method to cover a few cases where other mite species may be encountered. The levels of dust mite allergens were measured in 14 offices in response to numerous health complaints. Approximately one-half of the offices investigated were identified as having a dust mite population. Four offices showed levels of Der p I in the dust greater than 1 microgram/g. In two offices, the dust mite allergens were the source of the health complaints. In the other two offices, dust mite allergens were one of the contaminants in the office environment. In all cases, the infestation of dust mites in the offices was localized to a few specific work areas. Office chairs were the primary location where dust mites thrived. The remedial measures included regular cleanup of all fabric-covered office furnishings. Steam cleaning was recommended to eliminate dust mite populations.

Air Pollution, Indoor↗
PubMed2000

Long term dynamics of dermanyssus gallinae in relation to mite control measures in aviary systems for layers.

1. The dynamics of the poultry red mite, Dermanyssus gallinae, in aviary systems for layers were studied in an empirical study in Sweden between 1994 and 1997. Fluctuations were monitored with mite traps at monthly intervals during 3 laying cycles at each of 2 commercial poultry farms. 2. When mites were first detected in the system it then took about 5 months for the populations to reach equilibrium levels around which they fluctuated. Within flocks when the population growth was unaffected by temporary control activities, it was demonstrated that the mite populations were significantly denser in summer than in winter. 3. Current control methods had limited effects as mite populations were only temporarily suppressed. One exception was the control achieved with permethrin impregnated plastic strips, which reduced the population at equilibrium level to approximately 22%, compared with the previous flock. 4. The distribution of mites was patchy horizontally, along the aviary system, at low burden wlhereas it became more evenly dispersed at equilibrium. 5. Significant differences in vertical mite distributions that correlated with the hybrids used and their rearing conditions were also observed. In flocks with brown hens, mites gathered at the lower tiers, whereas they were found at the highest tiers in association with white hens. As the hens are attacked mainly at night-time the most likely explanation is that the mites adjust their behavioural pattern to the birds' roosting behaviour.

Animal Husbandry↗
PubMed1979

Mite allergen content in commercial extracts and in bed dust determined by radioallergosorbent tests.

Radioallergosorbent (RAST) direct binding and inhibition type assays were used to quantitate the mite (Dermatophagoides pteronyssinus) allergen content of four commercial mite extracts and a laboratory prepared extract from freeze-dried mites. The content of mite allergen in extracts prepared from twenty samples of dust vacuumed from bedding was measured by RAST inhibition assay. The four commercial mite extracts designated A, B, C and D, and the laboratory extract, designated L, contained 52, 265, 108, 1.5 and 581 arbitrary units of allergen/ml for the direct binding assay and 128, 111, 217, approximately 1 and 1083 arbitrary, but different, units of allergen/ml for the inhibition assay respectively. Qualitative differences between at least two extracts were suggested by the different slopes obtained when allergen binding of anti IgE was plotted against the volume of extract used in the direct binding assay. Differences in slope between the two extracts were also apparent when they were used in the inhibition assay. The quantities of mite allergen/gm of bed dust expressed in arbitrary units for the inhibition assay were 24 to 457 (mean 129) units. These quantities are similar to and sometimes greater than the quantity in 1 ml of mite extract and so confirm bed dust as a potent source of mite allergen. There was no significant correlation between the weight of dust, the numbers of dead and live mites and the allergen content of dust.

Allergens↗
PubMed1992

The house dust mite Dermatophagoides pteronyssinus is the most important allergen on the island of Mauritius.

To determine the relative importance of mites as a cause of allergic sensitivity and asthma on the western Indian Ocean island of Mauritius, we measured specific IgE antibodies to common inhalant allergens in sera from Mauritians claiming to have allergic symptoms and we examined house dust samples for evidence of mites and their allergens. Seventy-two of the 110 sera tested (65%) contained detectable IgE antibody to at least one mite, mould or pollen allergenic extract. By far the most prevalent was antibody to one or both of the common house dust mites, Dermatophagoides pteronyssinus and Dermatophagoides farinae, being present in 67 (61%) of the 110 sera. Allergy to pollens, including the locally prevalent Bermuda grass and sugar cane, was infrequent. Antibody to a limited number of moulds was detected in 22% of the sera tested. Of 81 subjects whose clinical history was known, 60 were asthmatic, and 75% of these asthmatic individuals had IgE antibody to mites. In contrast, only 35% of the subjects with rhinitis without asthma were sensitive to mites. Different mite species, including D. pteronyssinus but not D. farinae, were identified microscopically in samples of local house dust. Mite antigen Der p I but not antigen Der f I was detected with specific monoclonal antibodies in extracts of these dust samples. On the bases of this serological and environmental survey, we conclude that our data support the hypothesis that the house dust mite D. pteronyssinus is the principal cause of allergic sensitivity and asthma in that tropical environment.

Adolescent↗
PubMed1993

Exposure to house dust mite allergen of children admitted to hospital with asthma.

Eighty-two children admitted to hospital with exacerbations of asthma were studied to determine how many were exposed to house dust mites at the time of admission and displayed immediate hypersensitivity to house dust mites. The concentration of house dust mite allergen (Der p I) was measured in dust obtained from the child's mattress, bedroom floor and living room floor. Sixty-two (75%) children admitted had been exposed to > 10 microg Der p I/g. Sixty-seven (82%) children were sensitive to house dust mite (RAST > or = 1 +, or weal > or = 3 mm): 49 (60%) children were both exposed and sensitive. In contrast in a control group of 44 children, 31 (70%) (n.s.) were exposed to > 10 microg Der p I/g, 10 (23%) (P<0.001) were sensitive to house dust mite, and 7 (16%) (P<0.001) were both exposed and sensitive. Seventy-three homes were revisited 6 months after the child's initial admission. During the preceding month 14 children had been readmitted, 12 were fully investigated; of these 10 were both sensitive to house dust mite and still exposed to > 10 microg Der p I/g. In contrast, of the remaining 62 children who were not readmitted, only 19 were both sensitive and still exposed to > 10 microg Der p I/g (P<0.001). In conclusion, the majority of children admitted to hospital with exacerbations of asthma were exposed to house dust mite allergen and were house dust mite sensitive. Further the results suggest that continued exposure to higher concentrations of mite allergen may be associated with the risk of readmission.

Adolescent↗
PubMed1994

House-dust mite exposure reduction in specially designed, mechanically ventilated "healthy" homes.

Exposure to house-dust mites (Dermatophagoides spp.) was investigated in 30 asthmatic patients before and after moving to homes with mechanical ventilation systems. Median house-dust mite concentration was 110 mites per gram of mattress dust at the initial investigation and 20 mites per gram at the first follow-up after a mean of 4.7 months in the new homes. This was lower (P < 0.05) than counts in a control group of 23 asthmatic patients that had unchanged counts. At a second follow-up, after 15.0 months, mite counts in the study group were further reduced (P < 0.01) from initial values. Among 16 patients, with initial mite counts above the recommended threshold limit value (TLV) of 100 mites per gram of dust, the mite counts fell, in most cases, below this TLV. Air-exchange rates increased (P < 0.001) from a median value of 0.40 air changes per hour (ach) to 1.52 ach at the second follow-up investigation. Furthermore, a reduction (P < 0.01) was found in indoor absolute air humidity, with a median value of 5.6 g of water/kg. No such changes were found in the control group. The present study indicates that reduction of air humidity through an increased supply of fresh air may significantly diminish and, in some cases, even eliminate house-dust mites in homes.

Air Conditioning↗