Findings in vivo of Sarcoptes scabiei with incident light microscopy

ARTICLE

Human scabies is a frequent ectoparasitosis caused by the transmission of Sarcoptes scabiei. It is usually spread by skin-to-skin contact, although clothing and linen may act as fomites since the mite can remain viable away from skin for 2 to 5 days. The primary infestation has a month incubation period before allergic sensitization occurs and itching begins. Subsequent infestations produce immediate itching [1, 2].

Scabietic lesions are typically found on interdigital webs, elbows, feet, genitalia, buttocks and axillae. The head is usually spared in adults but is involved in infants. The burrow is the characteristic and diagnostic feature of the human scabies variant. Experienced observers can detect and even remove the female mite, which appers as a small dark of gray speck below the vesicle [3]. In many cases microscopic examination can be negative due, probably, to the small number of parasites in the cornified layer [4, 5].

Recently, Kreush suggested using light incident microscopy (with varying magnifications from x 6 to x 40) for in vivo detection of Sarcoptes scabiei to confirm diagnosis [6]. Many suspicious sites may be examined within a few minutes without causing any harm or discomfort to the patient. To improve the diagnosis we used a camera with lenses that allowed up to x 200 magnification.

We evaluated, the convenience and the applicability of this incident light microscopy in the diagnosis of scabies in thirty-seven patients.

Patients and methods

Thirty-seven patients with the presumptive clinical and/or anamnestic diagnosis of scabies were enrolled in our study.

For the incident light microscopy the following procedure was used: a) selection of suspected mite locations (burrows, nodule, papule) by the naked eye, b) application of citron oil and a slide to eliminate epidermal reflection, c) observation of selected areas with incident light microscopy using a Macroblitz color camera (Fig. 1) with interchangeable lenses and enlargement up to x 200 (greater enlargement up to x 1,000 with zoom), d) camera equipped with image sensor and halogen light through 28 optic fibers with temperature of 3,200 K, e) visualization is obtained with a RGB monitor (high definition). After finding the mites, we collected and observed them using an optical microscope in order to achieve an accurate estimation of the actual presence of Sarcoptes scabiei.

The examination with incident light microscopy highlighted the presence in the lesions of oval-shaped, translucent structures in whose anterior part it was possible recognize the anterior legs of the mite and the rostrum (Fig. 2); it was also possible to observe the burrow with excrement and egg deposits.

In all cases examined, we visualized the anatomical structures of the mite and afterwards confirmed the presence of the mite with traditional direct microscopy.

Discussion

The diagnosis of scabies is, at the moment, relatively difficult. In many cases, the results of microscopic examination can be negative.

Until 1992, epiluminescence microscopy was used only for preoperative assessment of melanocytic lesions. Then Kreush [6] suggested using this investigative method for the detection of Sarcoptes scabiei in vivo. This suggestion is supported by the fact that ELM allows a detailed inspection of the skin surface down to the superficial papillary dermis, where the scabies mites live.

The present study and a previous observation [6] suggest that incident light microscopy could represent the method of choice for the diagnosis of scabies; in fact, as regards the traditional optical microscope, it presents the indisputable advantage of allowing the observation, with enlargement up to x 200, of quite large body areas and clinical lesions. Most foreign bodies in the skin (e.g. splinters, etc.) are easily recognized, and their complete removal can be achieved. Finally, this method can be highly accurate in the location of the parasites by recognition of their anatomical structures.

A major advantage of a quick and accurate diagnosis is that it avoids the frequent phenomenon of multiple consultation. In line with Argenziano [7], we propose this technique in the newborn, children, the elderly and all patients with atypical disease.

REFERENCES

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