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House dust mites in urine. Spurious finding in two cases.


Mites belong to the order Acarina and only a few species are known to affect humans. Mites in sputum specimens were first reported in 1944 by Carter et al. in Ceylon (1). The acaroid mite is a kind of arthropod and its geographic distribution appears to be global and mites can survive in many environments including the storehouse, farmhouse, stored food stuff, various drugs, packing material, household objects, and human and animal bodies. Its infection in human cause acariasis in some organs including the lung, intestines, and the urinary tract by inhalation, ingestion, and transmission through the skin (2-4). House dust mites can also cause asthma and extensive dermatitis to atopic eczema through the allergens that they produce (5). Most adult mites possess the usual arachnoid appendages, jaws, palps at the front end, and four pairs of legs. This report describes the spurious cytologic findings of adult dust mites in urine samples from two patients. With referral from a parasitology laboratory, and experts on house dust mite identification, we concluded that the microscopic objects were most likely dust mites, the first case as being Euroglyphus maynei and the second case as being of the Dermatophagoides species (6,7).

From the laboratory perspective it may not be possible to decide whether the presence of mites is due to contamination or a true infection. The possibility of infection should only be considered in the presence of a considerable number of adult mites with inflammatory reaction (3) and after repeated identification of mites in consecutive samples from a symptomatic patient, and that the clinical findings are compatible with such an infestation. Mites can be present in cytologic samples as a contaminant from the environment. In this article we present two cases of urine samples in which we observed a single mite. Presence of a single mite without inflammatory reaction and relevant clinical findings led us to consider their presence as a contaminant.


Case 1: A 30 year old pregnant female presented with chronic haematuria without other symptoms. We received a urine sample from the urologist for cytologic examination in which we found an adult mite, originally mistaken for pubis lice. On two consecutive urine samples from this patient we did not find any adult mites. On examination by her general practitioner no visible opalescent nits or live lice and blue macules at feeding sites were present.

Case 2: A 72 year old female presented with haematuria and dysuria. We received a urine sample for cytologic examination in which we found single adult mite without inflammation. We did not receive any further urine samples from this patient.


In both cases we received fresh mid-stream urine samples in a summer month from the urologist for cytologic examination. Filter preparations were made on size 5 micron, 25 mm diameter Sartorius AG-cellulose acetate filters using the cytosieve method in which cells are trapped in filters pores and fixed in 95% ethanol. Filters were stained by the Papanicolaou method. The main components of Papanicolaou stain includes basic dye-hematoxylin, which stains the nucleus; and three acid dyes-light green, eosin, and Orange G, which stain the cytoplasm. With the Papanicolaou stain, the nucleus stains deep blue, nuclear details are sharp, the nucleous stains red, and the cytoplasm stains eosinophilic, cyanophilic, or orange (8).


Cytologic findings

Filter preparations of both urine samples demonstrated blood, benign squamous cells, scattered reactive urothelial cells and a single well preserved dust mite, approximately < 0.5 mm in size, pinkish brown in colour with partially folded legs (presumably 4 pairs), jaw, and palps at the front end (Figures 1 and 2). No inflammation was seen in both cases.


Mites belong to the order Acarina and are a kind of arthropod with only a few species known to affect humans (5-7). Mites are distributed throughout the world and thrive in warm, moist environments (7). They are tiny creatures less than 1 mm in length, usually invisible to the naked eye. Mites are found almost everywhere in nature, on land and in water, living on organic matter. The body of the mite is divided into two regions; a front part called the cephalothorax and a hind part called the abdomen. Although there is no clear demarcation between these parts, most adult mites possess the usual arachnid appendages, jaw and palps at the front end, and four pairs of legs. Most mites are quite harmless themselves but their fecal pellets contain digestive enzymes that can cause severe conditions such as asthma, allergic reaction, dermatitis, intestinal and urinary acariasis, and respiratory disorders (2,4,5).

A study in China found that the prevalence of human intestinal, respiratory and urinary acariasis (mite infection) was associated with occupation and was higher in individuals working with medicinal herbs, in store houses, in mills, or other sites where the density of mites was high (4). Nevertheless, mites can be found in cytologic samples as a contaminant from the environment, as we have observed in two cases of urine samples. In spite of their relative large size, mites are not always conspicuous because they are often transparent and unstained, and the joined appendages and sac-like bodies cause them to resemble specimen contaminants such as food. In many cases the legs are folded against the body rather than extended making the mites considerably less conspicuous and may be overlooked on routine screening, especially in cases of contaminants.

The differential diagnosis includes Sarcoptes scabie which are most commonly associated with humans and cause scabies with pruritus skin manifestations such as papules, blisters and eczematous changes. Pthirus pubis has a similar appearances but is normally bigger in size (1-3 mm long) and has broader crab like bodies with three pairs of legs, a small head with short antennae and simple eyes (9), which were absent in both our cases. Pthirus pubis infests hair in the pubic area and physical findings include visible opalescent nits or live lice, which were not present in our patients.

We conclude that the microscopic object in each urine sample were house dust mites that were contaminants because consecutive two urine samples from the first patient did not show any dust mite. One reason for house dust mites as a contaminant is the presence of house dust mites on clothing (10) and on skin (11) as evidenced by the presence of house dust mite allergens on these environments and thus may have been transferred into the urine specimens. In New Zealand 98% of house dust mites are Dermatophagoides pteronyssinus (12). They were first described in domestic homes in New Zealand in 1971 (13). New Zealand has some of the highest levels of house dust mite allergens in the world and this reflects the very high number of house dust mites in New Zealand domestic dwelling (14). The clinical significance of mites in cytologic samples largely depends on the identification of the mite species.


In our study, in the first case the mite was Euroglyphus maynei and the second being of the Dermatophagoides species (which was identified by an experienced house dust mite expert but he was unable to determine whether it was D. pteronyssinus or D. farina). To avoid contamination of urine specimens sterile specimen containers should be used when sampling and the container should be kept closed until ready for examination.


The authors acknowledge Louise Goosens for her photographic assistance, Rob Siebers for guidance towards the case, and Graeme Paltridge from Parasitology at Canterbury Health Laboratories. Adrian Pike from Victoria University, Wellington; and Dr Matt Colloff (CSIRO Ecosystem Sciences, Canberra, Australia) for helping us in identifying the dust mites; and Ian Thompson for graphical assistance.


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(3.) Farley ML, Mabry LC Hieger LR. Mites in pulmonary cytology specimens. Diagn Cytopathol 1989; 5: 416-426.

(4.) Li CP, Cui YB, Wang J, Yang QG, Tian Y. Acaroid mite, intestinal and urinary acariasis. World J Gastroenterol 2003; 9: 874-877.

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(6.) Abbott J, Cameron J, Taylor B. House dust mite counts in differenttypes of mattresses, sheepskins and carpets, and a comparison of brushing and vacuuming collection methods. Clin Allergy 1981; 11: 589-595.

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(8.) Gill GW, Frost JK, Miller KA. A new formula for a half-oxidized hematoxylin solution that neither overstains nor requires differentiation. Acta Cytol 1974; 18: 300-311.

(9.) Wendel K, Rompalo A. Scabies and pediculosis pubis: an update of treatment regimens and general review. Clin Infect Dis 2002; 35(Suppl 2): S146-151.

(10.) Riley G, Siebers R, Rains N, Crane J, Fitzharris P. Housedust mite antigen on skin and sheets. Lancet 1998; 351: 649-650.

(11.) Siebers RW, Patchett K, Fitzharris P, Crane J. Mite allergen (Der p 1) on children's clothing. J Allergy Clin Immunol 1996; 98: 853-854.

(12.) Pike AJ, Wickens K. The house dust mite and storage mite fauna in New Zealand dwellings. N Z Entomol 2008; 31: 1722.

(13.) Cornere BM. The incidence of house dust mites in Auckland. N Z J Med Lab Technol 1971; 25: 7-9.

(14.) Wickens K, Siebers R, Ellis I, Lewis S, Sawyer G, Stone L, et al. Determinants of house dust mite allergen in homes in Wellington, New Zealand. Clin Exp Allergy 1997; 27: 1077-1085.


Sharda Lallu, BSc CT(FIAC), Staff Cytotechnologist [1]

Sarla Naran, BSc CT(FIAC), Staff Cytotechnologist [1]

Peter Bethwaite, MBChB PhD FFSc(RCPA) FRCPA, Senior Lecturer [2]

[1] Department of Cytology, Anatomic Pathology, Wellington Hospital, Wellington

[2] Department of Pathology and Molecular Medicine, Wellington School of Medicine and Health Sciences, University of Otago, Wellington

Author for correspondence: Dr Peter Bethwaite. E-Mail:
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Title Annotation:CASE STUDY
Author:Lallu, Sharda; Naran, Sarla; Bethwaite, Peter
Publication:New Zealand Journal of Medical Laboratory Science
Article Type:Report
Date:Nov 1, 2014
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