An unusual case of processionary moth reaction

Dear Editors, The young one of the processionary moth is a larva of size ranging from 1 to 3⋅5 cm, with numerous hairs on them that are irritating for humans (1), which they use as a defence technique. The groups of processionary moth larvae always move in single row (it owes its name to this characteristic habit of moving on the ground in rows, forming a sort of ‘procession’) and shrink when they reach their nest of a white, silk-like material. The nest is used to lay eggs; after the hatch it is abandoned and new larvae will need to rebuild it. The so-called triangular butterflies are nothing more than the processionary adults and are totally harmless, although they are nocturnal and and they don’t settle down easily in inhabited homes. Their size can be variable, but mostly range 3–4 cm and the colour of their wings vary from dirty white to light ivory yellow, with streaks of darker colour almost invisible. The wingspan is about 5 cm. When threatened, the moths spray a yellowish liquid irritant and then fly away. The moth is an insect common in the temperate regions of the Mediterranean Sea basin. The caterpillar of the pine processionary moth is regarded as one of the main limiting factors for the development and survival of the pine forests of the Mediterranean region. This is because the moths attack mainly plants of the species Pinus nigra (black pine) and Pinus sylvestris (Scots pine), but sometimes also damage Pinus halepensis, Pinus pinea and Pinus pinaster; they rarely attack Pinus strobus, and it is not uncommon for the pine processionary moth to attack larch and cedar as well. The nests of the pine processionary moth, which overwinter as larvae, are recognisable even at a distance; are pear-shaped and brilliant white, mostly located on the top of the tree and at the tips of the lateral branches. Nests are filled with excrement and exuviae of the adults. In October 2013, a 55-year-old male was referred to our department for erthematous and squamous macules with atrophy of the hair follicle. The patient also had light itching at the site. We decided to perform skin biopsy, which showed an inflammatory infiltrate and the presence of many species belonging to the Trichophyton mentagrophytes family. The patient admitted visiting pine woods in which there were many processionary moth nests. Since similar wounds were reported by other people who frequented the same woods, we decided to analyse the nests of processionary moths with which the patient was in contact. Inside the nest we found the same fungi that we found on the skin of the patient. The stinging hairs of the processionary larvae easily separate from the larva back, during a contact or under the wind (2). Because of their particular structure (with tiny hooks at their end), these hairs will stick easily to the tissues (skin and mucous membranes), causing a stinging reaction due to the release of histamine (substance released in allergic reactions) (3). Those having repeated contact with the moths had reactions that got worse with each new contact. In severe cases, anaphylactic shock can occur with fatal consequences (hives, sweating, swelling in the mouth and throat, difficulty breathing, hypotension and loss of consciousness). There are many different symptoms, depending on the affected site of the body: • In the skin, direct contact with nests or processionaries led to dermatitis. Alternatively, an aeromediated contact with dispersed urticarial hairs causes skin, ocular and respiratory conditions. We usually find intense and continuous itching, with typical eruption and manifestation with round macules and papules (4). These can be surmounted by vesicles. Scratchy lesions are common findings, not only at the contact site but also in the rest of the body, because of the dispersion of the hairs. • In the eyes, hairs contact lead to an immediate, unilateral, burning sensation, with hyperemia and edema of conjunctiva and eyelids. If the hair goes deep into the eye tissue, it can cause inflammatory reactions and, rarely, blindness. • Hairs inhalation can evolve into respiratory symptoms with rhinitis, cough, dysphagia and dyspnea. Asthma crisis and risk of asphyxia are possible and are caused by an airway narrowing.