Prevalence and Species Distribution of House Dust Mites in Household Dust Samples from Homes of Individuals with Allergic Complaints in Ordu, Turkey

Summary

This cross-sectional household survey investigated the presence and species distribution of house dust mites in clinically selected homes in Ordu Province, Turkey. Dust samples were collected from 160 households, and mite species were identified microscopically to determine environmental mite prevalence.

Abstract

This environmental cross-sectional study investigated the prevalence and species distribution of house dust mites in household dust samples collected from homes of individuals presenting with allergic complaints in Ordu Province, Turkey. Dust samples were collected from 160 households of individuals reporting asthma or other allergic complaints during outpatient clinic visits. Allergic conditions were based on participants’ self-reports and were not clinically confirmed. Samples were obtained from various areas of the home, including bedrooms and living spaces, using a portable vacuum cleaner, and were examined microscopically following the lactic acid precipitation method. Species identification was performed on positive samples using standard morphological keys. House dust mites were detected in 105 (65.6%) households, with detections throughout the year. The most frequently identified species were Dermatophagoides pteronyssinus, Dermatophagoides farinae, Dermatophagoides spp., Cheyletus spp., Chortoglyphus arcuatus, Acarus siro, Glycyphagus domesticus, Oribatida spp., and Euroglyphus maynei. Statistical analyses showed no significant association between mite presence and most demographic, environmental, or housing-related variables; however, age was identified as a factor associated with mite positivity. The findings indicate that house dust mites are highly prevalent in households within this humid Black Sea region and highlight their potential relevance for individuals with atopic conditions. Providing patients and their families with practical information on household mite control measures can improve indoor environmental quality and symptom management.

Introduction

House dust mites are arthropods commonly found in human settlements. Due to their microscopic size, they often go unnoticed and persist in living spaces. These organisms feed primarily on shed human and animal skin particles; fungal spores and various organic particles are also among their food sources. The life cycle and population density of mites depend on environmental factors such as temperature, relative humidity, and food availability. Indoor environments with suitable microclimatic conditions favor mite proliferation^1,2,3.

The importance of house dust mites in environmental exposure was first recognized in the early 20th century; the relationship between these organisms and the indoor environment was established in conjunction with respiratory complaints observed among individuals working in flour mills¹. Following Cooke's attention to the allergenic components in house dust, Voorhorst et al. (1967)⁴ demonstrated that mites were the primary biological source of house dust, a finding that is considered a significant milestone in indoor environmental exposure studies.

Among animal-derived allergens, 19 respiratory, 28 food, and 3 venom allergens have been identified, and it is noted that the number of allergens reported in the literature has increased over time⁵. Mite-derived antigens can accumulate in household materials such as beds, quilts, pillows, bedding, upholstered furniture, carpets, and textile products made of cotton, wool, feathers, or other fibers. These antigens can be released into the environment through the use of these materials or mechanical movements and spread through the air. It has been reported that some Group II antigens have a particle size smaller than 5 µm and can therefore be present in the respirable fraction⁶.

Li et al. (2009)⁷ reported that a certain number of mites can produce a significant amount of antigen daily. It has been emphasized that high levels of environmental exposure, especially during childhood, may be important for the development of sensitization; this may vary depending on individual and environmental factors^8,9,10. However, it is noted that most of these relationships have been evaluated based on levels of environmental exposure, and that causal inferences regarding clinical outcomes should be made with caution.

It has been reported that the prevalence of allergic diseases increases by approximately 1% annually; it has been suggested that this increase may be related to changes in environmental factors rather than advances in diagnostic methods¹¹. Factors such as global climate change, air pollution, increased pollen exposure, and the rising frequency of extreme weather events have been suggested as possible contributors to environmental allergen exposure¹². Asthma is reported to be one of the most common chronic diseases worldwide, with prevalence varying between 1% and 18% depending on the region¹³.

The distribution and prevalence of house dust mites may be influenced by factors such as climatic characteristics, housing structure, sampling method, and sampling frequency, as highlighted in the literature^7,14. However, studies with large sample sizes and a single sampling method are limited, especially in regions with humid climates such as the Black Sea Region. This situation necessitates assessing the presence and distribution of house dust mites at the regional level in the context of environmental exposure.

The aim of this cross-sectional and descriptive study is to determine the prevalence and species distribution of house dust mites in house dust samples collected from residences in Ordu province, where the annual average temperature is 14.4 °C and relative humidity ranges between 60%–90% during the summer months, and to evaluate environmental and demographic factors that may affect mite presence. The study hypothesizes that the humid and temperate climate of Ordu province creates suitable microclimatic conditions for house dust mite presence and that mite prevalence may vary with indoor environmental factors.

Protocol

This study was approved by the Ordu University Clinical Research Ethics Committee (Approval No: 09/11/2017–138). The study was conducted in accordance with relevant institutional and national ethical guidelines, including the Declaration of Helsinki. Written informed consent was obtained from all participants included in the study. The consent obtained explicitly covers conducting home visits and collecting house dust samples from residences.

1. Study design

This is a cross-sectional, descriptive study of house dust mite prevalence conducted in the province of Ordu, Turkey. Household dust samples were collected from specific indoor surfaces where mite accumulation is commonly expected. Sampling was performed from mattresses, bedding materials (pillows and quilts), carpets, and upholstered furniture located in bedrooms and living rooms. Dust was collected with a portable vacuum cleaner, and samples from different locations within the same household were pooled to form a composite household dust sample.

2. Study population and clinical cohort definition

The study population consists of individuals who visited the Ear, Nose, and Throat and Internal Medicine Outpatient Clinics at Ordu University Faculty of Medicine Education and Research Hospital due to asthma and/or allergic complaints. The inclusion criteria for participants were being 18 years of age or older, consenting to the collection of dust samples from their home environment, and agreeing to answer the questionnaire. Individuals who did not consent to a home visit, did not provide written consent, or for whom sufficient home dust samples could not be obtained were excluded from the study. Clinical diagnoses were assessed based on patients' self-reports and reasons for outpatient clinic visits; no clinical verification or diagnostic testing was performed. Each patient was matched with a household, and analyses were conducted at the household level. Ordu Province is located in the Eastern Black Sea region of Turkey and features a humid, temperate climate with year-round high humidity, conditions that may favor the survival and proliferation of house dust mites.

3. Sampling unit and sampling method

The primary sampling unit for this study was the household. Multiple sub-dust samples were obtained from different indoor locations within each household, with a particular focus on bedrooms and living areas. Although these sub-samples were collected separately, they were pooled and analyzed as a single composite household dust sample in the laboratory to represent overall indoor mite exposure. To estimate mite density, approximately 1 g of dust from each composite household sample was processed using the lactic acid precipitation method. All mites observed in the prepared microscopic slides derived from this dust sample were counted. The total number of mites detected was then expressed as the number of mites per gram of house dust.

Each household was sampled only once, and no repeated sampling was performed. Household dust samples were collected using disposable dust bags assigned to each sampling area, and a portable vacuum cleaner with a suction power of 1200 W. Sampling was conducted at a standardized rate of approximately 2 min/m² to ensure consistency and reproducibility across all households.

4. Laboratory procedures and mite identification

Once the samples were brought to the laboratory, they were sieved to remove coarse particles. The samples were examined by the lactic acid precipitation method. The lactic acid precipitation method was used to clarify dust samples by dissolving organic debris, facilitating the separation and visualization of mites and enabling reliable microscopic detection and morphological identification. One gram of house dust was added to 5 mL of 90% lactic acid in test tubes. The tubes were gently mixed and incubated for 1 h. After incubation, samples collected from both the surface and the bottom of the liquid were mounted between a slide and a coverslip and examined under a light microscope at 100×, 200×, and 400× magnifications¹⁵. Species identification was subsequently performed on dust samples in which mites were detected.

Samples in which mites were detected were defined as “mite positive”. The presence of at least one mite in any developmental stage (larva, nymph, or adult) in a dwelling was considered sufficient for the dwelling to be considered mite positive. For species identification in positive samples, mites visible under a stereomicroscope were collected using a fine-tipped insulin syringe needle after filtration from the supernatant onto filter paper and were mounted in Hoyer’s medium. Prepared specimens were examined under a light microscope for morphological identification. Statistical analyses were performed using statistical analysis software^{16,17,18,19,20}. Specimens were identified to species, genus, or higher taxonomic levels depending on the developmental stage and the availability of diagnostic features. Dermatophagoides spp. includes larval, protonymph, and deutonymph stages that could not be reliably identified to the species level. Oribatida represents mites identified at the order level. Unidentified larva and nymph refer to immature specimens, and unidentified imago to adult specimens, that could not be taxonomically classified due to insufficient or damaged morphological characteristics. The total number represents the cumulative count of all mite individuals detected across positive samples.

5. Survey application and variable definitions

A survey containing questions about demographic characteristics, housing structure, environmental factors, and allergic complaints was administered to participants. Data were evaluated based on participants' statements and were not clinically verified.

6. Statistical analysis

The association between categorical variables was examined using the chi-square test, and the change in mite density according to demographic and vital characteristics was examined using the Mann-Whitney U or Kruskal-Wallis tests. Binary logistic regression was used to examine the association between the dependent variable (mite positivity) and the independent variables. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated.

Results

Species distribution
Taxa are reported at the species or genus level where morphological identification was possible; specimens identified only at higher taxonomic levels are explicitly indicated. In the study, dust samples from 160 households were examined. Dust mites were detected in 105 households, while 55 households were evaluated as negative. Mite density values were calculated based on the total number of mites observed in microscopic preparations obtained from 1 g of house dust.

Discussion

Table 6 compares the prevalence of house dust mites across different countries and regions of Turkey, along with sampling design, sample size, and climatic characteristics. When studies are examined, it is seen that mite prevalence is generally higher in regions with hot, humid climates; in particular, positivity rates reached 100% in studies in which samples were collected at regular intervals from the same residences. In contrast, prevalence rates were lower in studies using a single sampling method an...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Portable vacuum cleaner (1200 W)	Arcelik	S 7564	Used for household dust collection
Disposable vacuum dust bags	Arcelik	Compatible with S 7564	Single-use for each household
Sieve (fine mesh)	Isolab	092.01.001	Removal of coarse particles
Test tubes (15 mL)	Isolab	077.01.015	For lactic acid precipitation
Lactic acid (90%)	Merck	100135	Dust clarification
Light microscope	Olympus	CX43	×100, ×200, ×400 magnifications
Stereo microscope	Olympus	SZ61	Collection of visible mites
Microscope slides	Isolab	064.01.001	Sample preparation
Cover slips	Isolab	064.02.001	Sample preparation
Hoyer’s medium	Sigma-Aldrich	H3147	Mounting medium for mites
Syringe tips (PP)	Eppendorf	30000813	Mite transfer
Filter paper	Whatman	Grade 1	Filtration of supernatant
RPMI-1640 medium	Gibco	11875-093	Parasite propagation
Statistical analysis software	IBM	SPSS v22.0	Data analysis