Monica Corazza1, Massimo Tassinari2, Marco Pezzi3, Michela Ricci1, Alessandro Borghi1, Sara Minghetti1 and Marilena Leis3
Departments of 1Medical Sciences, Section of Dermatology and 3Life Sciences and Biotechnology, University of Ferrara, Via Savonarola 9, IT-44112 Ferrara, and 2DVM, Animal Health Sector, Public Health Department, Azienda USL of Ferrara, Ferrara, Italy. E-mail: czm@unife.it
Accepted Apr 5, 2013; Epub ahead of print Aug 27, 2013
Mites are an important cause of human dermatosis. Although clinical diagnosis is often simple for the clinician, the identification of the causative mite is often troublesome. The identification and eradication of the agent causing the eruption is crucial for the resolution of the cutaneous disease (1). We describe here a case of Pyemotes dermatitis in which infested wood was the source of the problem.
CASE REPORT
A 35-year-old non-atopic man presented an intensely pruritic eruption he had had for 2 days.
Skin examination showed numerous scattered, small, erythematous, urticarial papules distributed over the trunk and forearms. Each papule was capped by a tiny vesicle or had a central haemorrhagic punctum (Fig. 1). The palms, soles and mucous membranes were spared. Past medical history was of no significance. The patient’s wife had few similar lesions on her forearms.
A clinical diagnosis of multiple insect bites was made; however, the patient did not remember having been bitten and denied any contact with pets. On careful questioning he reported handled and having stored beech wood.
Fig. 1. Papulourticarial rash caused by Pyemotes ventricosus.
Examination of the wood revealed infestation by white larvae, sized 1–1.3 cm. Some specimens of larvae, together with sawdust, were delivered to the Animal Health sector of the Public Health Department and then the material (wood particles eroded as well as larvae of woodworms and their droppings) was taken to the University Laboratory of Urban Ecology and processed for scanning electron microscopy (SEM) analysis (Fig. 2). The larvae were recognized as belonging to the Cerambycidae family and they were infested by mites of the Pyemotidae family. The mites, present in large numbers, were physiogastric females (Fig. 3) identified as Pyemotes ventricosus (Newport, 1850) on morphological and behavioural basis (2).
Fig. 2. Scanning electron microscopy analysis of a physiogastric female of Pyemotes ventricosus.
Fig. 3. Two physiogastric females (female with enlarge abdomen) of Pyemotes ventricosus on a bckground of sawdust particles (optical microscopy). Arrows indicate the rear part of the ball-shaped histerosoma (posterior abdomen).
The patient was treated with oral antihistamines and systemic corticosteroids at tapering daily dosage.
Removal of the wood led to resolution of the dermatitis.
Discussion
P. ventricosus is a white-yellow predaceous mite that attacks and kills larvae or nymphs of a number of insects, including moths, beetles, wasps and bees, etc., that are usually found in grain, straw, plant-based food, firewood and old furniture. However, if normal food sources are reduced, P. ventricosus may attack horses, cattle, other mammals and humans. Human infestation occurs only accidentally and temporarily, when an individual comes in contact with infested material.
The skin eruption caused by P. ventricosus is known as “grain itch”, “barley itch”, “straw itch”, “hay itch”, “prairie itch”, “mattress itch” and “cotton seed itch” (3). It may be an occupational condition in farmers, bakers, dock-workers, packers and indoor workers. Both isolated cases and small outbreaks have been reported (1–5).
The first sign of this dermatitis is itching, which usually occurs within a few hours of contact with infested material, followed by an eruption of urticarial papules surmounted by pin-point vesicles, 10–20 h later. The vesicles are often destroyed by scratching (3). P. ventricosus bites are painless and therefore not correlated with dermatitis by the patient (6). A central hemorrhagic punctum is frequently seen; ecchymoses and brownish pigmentation may persist after resolution. The distribution of the eruption depends on the circumstances of the contact, and to some extent on the ambient temperature, which may condition the nature of the protective clothing worn at the time. Bacterial super-infections and systemic symptoms (fever, vomiting, and joint pain) are seldom described.
The mites are not visible to the naked eye, and reside only briefly on the human body, and thus are not found by physicians during clinical examination; the diagnosis is often based only on clinical features and patient’s history (1–7). The patient is often reluctant to accept the diagnosis of insect bites, so the definitive diagnosis can be made only through mite identification. This may persuade the reluctant patient to carry out disinfestation and environmental prophylactic measures.
Although Pyemotes spp. have been known since 1901 to cause dermatitis, only few documented cases have been reported in the literature. Even though P. ventricosus has been mainly reported to be associated with Anobium punctatum (1, 3), the common furniture beetle, exceptionally P. ventricosus can attack Cerambycide and Buprestidae (8), both damaging beetles, as in the present report.
The authors declare no conflicts of interest.
References
