Presently, approximately 10 million Chinese children suffer from asthma and about 50 million Chinese adults have allergic rhinitis [
China is large, and its climate varies from tropical zone to cold temperate zone. It is evident that the predominant allergenic mite species differ across diverse regions of China [
There are no reports about HDM surveys in tropical rainforest area of China. In the present study, to improve our understanding of the national epidemic of allergic diseases in China, we investigated the distribution of HDM in Xishuangbanna Dai, P.R. China, which is a special city in a tropical rainforest biome. We compared mite distributions in Xishuangbanna area homes between its rainy and dry seasons and compared the seasonal distributions in Xishuangbanna and in Beijing [
The survey subjects included a case group and a control group. The case group consisted of 31 homes of patients who were admitted to Xishuangbanna Dai Autonomous Prefecture Hospital and diagnosed by specialists with mite-related allergic diseases between August 2010 and January 2011. Their diagnoses were based on comprehensive considerations about disease history, symptoms, signs, skin prick test results, and serum sIgE test results. The case group only included homes where patients had positive skin prick test results from
Dust samples were collected with a 1200 W vacuum attached securely to an ALK Dust Trap (ALK. Copenhagen, Denmark) with a vacuum hose and O-ring and a measuring device to define 1 m2 of collection area or a scale. The filter dish was removed carefully to prevent dust spillage. Each collection dish was covered with a lid, sealed, and labeled with date and place information. The vacuum nozzle was stored vertically to prevent dust from falling out after vacuuming. The nozzle was rinsed and dried before being fitted with a new filter dish for collection of the next sample.
Collection sites were locations where mites survive and breed easily (i.e., pillows, quilts, sheets, sleeping pads and mattresses, sofas, rugs, and carpet floors). Collections were made by placing the vacuum nozzle over a defined 1 m2 area for 3 minutes. Samples were collected from the entire selected surface. The collection time was shortened to 2 minutes for places with surface area less than 1 m2 (such as pillows, sofas, and rugs).
All dust samples were collected and prepared by two researchers (Qing-Hua Luo and Yu-Ling Zhou). For each sample, a record of which collection device and filter plate were used, the collection location, and other related information such as the family’s living conditions was kept. Dust samples were transported to the lab in Xishuangbanna. Whenever possible, the mites within the samples were isolated immediately; otherwise, they were stored frozen at −20°C for later isolation [
The flotation method was used to extract mite bodies from the dust samples. Isolated mite specimens were stored in 70% alcohol. For convenient morphological species identification of individual mites, permanent slides were prepared using Hoyer’s Medium and observed under a light microscope. Species were identified in accordance with the morphological characteristics described by Krantz and Walter and other related information [
The mite-positive rate of samples was calculated as follows: positive rate is positive sample number/total sample number × 100%. The number of mites in each mite species within each sample was counted, and the percentage of each species relative to the total mite counted for each sample was calculated. All mite bodies were counted, whether they were alive, dead, or physically damaged. Mite density was calculated for each sample as follows: mite density is total number of mites detected/weight of isolated dust (in g). If the number of mite species obtained from the same location at different time points differed, the average number was used for the distribution calculations. The Xishuangbanna HDM data obtained in this study were compared to analogous data from a study conducted in Beijing during the same time span from December 2008 to January 2010 (
Rank sum tests for two independent samples (Mann-Whitney
A total of 233 dust samples were collected from 41 homes in the Xishuangbanna area between August 2010 and February 2011. Mites were detected in 186/233 samples (79.8%) and 40/41 homes (97.5%). In total, 6,349 live, intact mites in various development stages were detected. They were distributed among 877 slides. Species identification was possible for 6316/6349 of the mites. This group of 6316 identified specimens (the damaged remains of dead mites were not identified) included mites spanning 23 species in 15 genera, representing 12 families belonging to 3 orders of Acari. Notably, the four main allergenic HDM including
Composition of mites and insects in house dust in Xishuangbanna area.
Species | Sampled homesa,b ( |
Samplesb ( |
Mitesc ( |
|||
---|---|---|---|---|---|---|
Number | % | Number | % | Number | % | |
Acari | 40 | 97.56 | 186 | 79.83 | 6316 | 99.48 |
Astigmata | 40 | 97.56 | 183 | 78.54 | 6157 | 96.98 |
Pyroglyphidae | 40 | 97.56 | 182 | 78.11 | 6102 | 96.11 |
|
40 | 97.56 | 167 | 71.67 | 4001 | 63.02 |
|
38 | 92.68 | 126 | 54.08 | 1128 | 17.77 |
|
20 | 48.78 | 39 | 16.74 | 101 | 1.59 |
Nymph | 38 | 92.68 | 126 | 54.08 | 818 | 12.88 |
Larva | 19 | 46.34 | 27 | 11.59 | 54 | 0.85 |
Acaridae | 14 | 34.15 | 19 | 8.15 | 34 | 0.54 |
|
10 | 24.39 | 16 | 6.87 | 28 | 0.44 |
|
3 | 7.32 | 3 | 1.29 | 6 | 0.09 |
Glycyphagidae | 13 | 31.71 | 16 | 6.87 | 19 | 0.30 |
|
10 | 24.39 | 16 | 6.87 | 19 | 0.30 |
Histiostomatidae | 2 | 4.88 | 2 | 0.86 | 2 | 0.03 |
Oribatida | 5 | 12.20 | 8 | 3.43 | 26 | 0.41 |
Haplochthoniidae | 5 | 12.20 | 8 | 3.43 | 25 | 0.39 |
Unidentified | 1 | 2.44 | 1 | 0.43 | 1 | 0.02 |
Prostigmata | 27 | 65.85 | 54 | 23.18 | 123 | 1.94 |
Cheyletidae | 27 | 65.85 | 54 | 23.18 | 123 | 1.94 |
Mesostigmata | 5 | 12.20 | 8 | 3.43 | 10 | 0.16 |
Blattisociidae | 3 | 7.32 | 6 | 2.58 | 8 | 0.13 |
Laelapidae Berlese | 2 | 4.88 | 2 | 0.86 | 2 | 0.03 |
|
||||||
Insecta | 10 | 24.39 | 12 | 5.15 | 33 | 0.52 |
Liposcelididae | 6 | 14.63 | 6 | 2.58 | 22 | 0.35 |
Unidentified | 6 | 14.63 | 7 | 3.00 | 11 | 0.17 |
|
||||||
Total number identified | 40 | 97.56 | 186 | 79.83 | 6349 | |
Total number collected | 41 | 233 |
The numbers and percentages of individual arachnids and insects of particular species are reported in Table
Among the predominant Pyroglyphidae mites, most were adults (85.7%), followed by nymphs (13.4%) and larvae (0.9%).
The detailed counts and percentages of mites of the particular species of mites observed are reported in Table
Multiple mite species were often found within homes and within dust samples. Among the 41 surveyed homes, 2 homes had eight species of mites, 1 had seven species, 2 had six species, 6 had five species, 14 had four species, 11 had three species, 3 had two species, 1 had one species, and only 1 home had no mites. The predominant mite species was
Domestic mite densities in Xishuangbanna area are shown by season in Figures
Comparisons across the seasons of total mite (a),
Comparison of mite density in different seasons for 18 sites
Comparison of
Comparison of
Comparison of
The mite densities and positivity rates in the Xishuangbanna area differed markedly from analogous data for samples collected in the Beijing area (December 2008 to January 2010) [
As reported in detail in Table
Comparisons of the mite density in case homes versus control homes.
Group (number of samples) | Mite density, number of samples (%) | ||
---|---|---|---|
Lowa | Mediumb | Highc | |
Case ( |
110 (57.3%) | 59 (30.7%) | 23 (12.0%) |
Control ( |
21 (51.2%) | 12 (29.3%) | 8 (19.5%) |
Note: the value of row mean score differ test was 1.2184 and the
The present results confirm that home dust mites exist in Xishuangbanna area. We found that
The factors affecting the distribution and abundance of mite species are quite complex, involving not only geographical factors such as latitude, seasonality, climate, rainfall, altitude, and distance from a coast, but also household factors such as neighborhood location, building age and materials, house orientation, ventilation and thermal systems, family economic conditions, surrounding foliage, types of furnishings, and number of occupants and their smoking status and health habits [
Mite densities and positive detection rates were significantly lower in Beijing than in Xishuangbanna, perhaps due to their different geographical and climate characteristics and the large difference in latitude between the two areas. Indeed, it is not surprising that dust mites would be present in large numbers in tropical areas, such as Xishuangbanna, with mild temperature changes and a high relative humidity, which are optimal conditions for growth of the dust mites.
We observed no differences between the homes of mite-allergic people (case group) and homes of nonallergic people (control group) in terms of overall mite densities, nor in terms of numbers of homes with low, medium, or high densities of mites. Experts at an international seminar regarding mites and asthma held in 1988 reached a consensus that mite density of more than 100 mites per g of dust is a risk factor for sensitization and development of asthma (our cut-off between low- and medium-density samples) and that a mite density of more than 500 mites per g of dust is a risk factor for development of acute asthma attacks in mite-allergic patients (our cut-off between medium- and high-density samples). These cut-off values were used in our case versus control comparisons because they have been accepted indicators in mite research internationally for the last two decades [
In conclusion, the present study showed that the HDM population in Xishuangbanna area has its own characteristics. It has rich dust mite species. Four main allergenic dust mite species including
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank Professor Thomas A. Platts-Mills at the Asthma & Allergic Diseases Center, University of Virginia, USA, for assistance with this research.