Skin reactions induced by experimental exposure to setae from larvae of the northern pine processionary moth (Thaumetopoea pinivora)

Occupational Exposure of Forest Workers to the Urticating Setae of the Pine Processionary Moth Thaumetopoea pityocampa

The larvae of the pine processionary moth are a threat to public health because they produce detachable setae that are about 200 µm long and 6 µm wide, reaching a total number of up to 1 million per mature individual. The setae are intended to be released to protect the larvae from predators but become a public health issue when in contact with humans and warm-blooded animals. Symptoms associated with the setae are typically urticaria and local swelling erythema, although edema of the skin, conjunctivitis or respiratory mucosa may occur. Occupational exposure concerns mainly forest workers but also farmers and gardeners. In the present study, we quantify the exposure to the setae of forest workers in a district of Northern Italy. The pine processionary moth represents a real case of occupational exposure as the urticating setae produced by the larvae caused symptoms in most forest workers directly in contact with the infested trees. In addition, the urticating setae were detected on the body of the chainsaw operators and in the surroundings of the felled trees during the operations. The non-exposed workers of the same agency did not report symptoms, with only one exception, likely linked to a non-occupational exposure. As the risk is not immediately perceived by the workers because direct contact with the larvae is unlikely, a campaign of information to workers and the general population living nearby infested forestry areas about the risk associated with airborne exposure is recommended. This becomes especially important in the areas of recent expansion of the insect, where people are inexperienced.

Caterpillar Venom: A Health Hazard of the 21st Century

Caterpillar envenomation is a global health threat in the 21st century. Every direct or indirect contact with the urticating hairs of a caterpillar results in clinical manifestations ranging from local dermatitis symptoms to potentially life-threatening systemic effects. This is mainly due to the action of bioactive components in the venom that interfere with targets in the human body. The problem is that doctors are limited to relieve symptoms, since an effective treatment is still lacking. Only for Lonomia species an effective antivenom does exist. The health and economical damage are an underestimated problem and will be even more of a concern in the future. For some caterpillar species, the venom composition has been the subject of investigation, while for many others it remains unknown. Moreover, the targets involved in the pathophysiology are poorly understood. This review aims to give an overview of the knowledge we have today on the venom composition of different caterpillar species along with their pharmacological targets. Epidemiology, mode of action, clinical time course and treatments are also addressed. Finally, we briefly discuss the future perspectives that may open the doors for future research in the world of caterpillar toxins to find an adequate treatment.

Processionary Moths and Associated Urtication Risk: Global Change-Driven Effects

Processionary moths carry urticating setae, which cause health problems in humans and other warm-blooded animals. The pine processionary moth Thaumetopoea pityocampa has responded to global change (climate warming and increased global trade) by extending its distribution range. The subfamily Thaumetopoeinae consists of approximately 100 species. An important question is whether other processionary moth species will similarly respond to these specific dimensions of global change and thus introduce health hazards into new areas. We describe, for the first time, how setae are distributed on different life stages (adult, larva) of major groups within the subfamily. Using the available data, we conclude that there is little evidence that processionary moths as a group will behave like T. pityocampa and expand their distributional range. The health problems caused by setae strongly relate to population density, which may, or may not, be connected to global change.

Size and dispersion of urticating setae in three species of processionary moths

Larvae of the processionary moths of the Palaearctic region bear urticating setae that are released against vertebrate predators, especially insectivorous birds. A few species are pests of forest and urban trees and, consequently, may threaten human and animal health during outbreaks, causing dermatitis, conjunctivitis and respiratory distress. Although some studies provide detailed information about the setae, particularly those of the pine processionary moth Thaumetopoea pityocampa, there is little knowledge on the morphological traits of the setae and their release by the larvae. In the present study we identify major traits of the setae of 3 species of processionary moth, T. pityocampa, T. pinivora and T. processionea, which are potentially helpful in the understanding of setae dynamics in the environment: (i) diameter and length of setae and (ii) analysis of dynamical properties of the setae in the airborne state. Setae are highly variable in size, with bimodal distribution in T. pityocampa and T. pinivora; in these 2 species, short and long setae are interspersed within the integument fields where they occur. The difference in the seta size has important consequences in dispersion, as smaller setae can spread 5 times further than their bigger counterparts. This information is relevant for a full understanding of the defensive importance of larval setae against natural enemies of the processionary moths, as well for elucidating the importance of the processionary setae as air pollutants, both close to the infested trees and at longer distances.

Setae from larvae of the northern processionary moth (Thaumetopoea pinivora, TP) stimulate proliferation of human blood lymphocytes in vitro

Larvae of the Northern pine processionary moth (Thaumetopoea pinivora, TP) carry microscopic needles (setae), which by penetrating skin and mucous membranes, may cause inflammatory/immune derived symptoms in man. In the present study the stimulatory effects of setae on human blood lymphocytes in vitro was investigated. Blood mononuclear cells were separated from venous blood or buffy coat of ten healthy individuals, six previously exposed to setae and four with no known exposure. Lymphoproliferation was measured as uptake of ³H-thymidine. Setae were prepared from TP larvae. Setae and saline setae extracts stimulated proliferation of T-lymphocytes in the presence of monocytic cells. Stimulation was pronounced in cells from persons who had been exposed to setae, and weak in cells from non-exposed donors. Chitin also induced lymphocyte proliferation in most donors, but to a lesser extent and independently of donor's previous exposure to setae. In conclusion, setae contain molecules that in the presence of monocytes activate human T-lymphocytes to proliferation. The antigenic nature of stimulatory molecules was supported by the significantly stronger lymphocyte response in persons previously exposed to setae than in non-exposed donors. The nature of such molecules remains to be defined.

Mast cells respond to urticating extract from lepidoptera larva Morpheis ehrenbergii in the rat

Mast cells and histamine participate in toxic effects of hairs from some caterpillars. This study reports that a crude extract of Morpheis ehrenbergii caterpillar hairs induces in vitro mast cells activation, triggers the release of histamine and causes a rapid urticarial reaction in the rat skin. Heating of the extract abolishes the inflammatory reaction. These results suggest that the use of antihistamines may improve the adverse skin reactions caused by the Mexican caterpillar M. ehrenbergii.

Skin Reactions to pine processionary caterpillar Thaumetopoea pityocampa Schiff

Pine caterpillar, Thaumetopoea pityocampa Schiff, is a phyto- and xylophagous lepidopteran, responsible for the delay in the growth or the death of various types of pines. Besides nature damage, pine caterpillar causes dermatological reactions in humans by contact with its irritating larvae hairs. Although the dermatitis occurs among outdoor professionals, it is primarily extraprofessional. Contamination generally occurs in pinewoods, rarely in cities. Means of contamination comprise direct contact with the nest or the processional caterpillar and indirect contact with air dispersed hairs. The dermatitis is generally observed in late spring and particularly from April to June, among campers and tourers. The eruption has its onset 1-12 hours after contact with the hairs and presents with intense and continuous itching. Morphologically, it is strophulus-like and consists of papulous, excoriated, and pinkish lesions on an oedematous base. Diagnosis is usually straightforward. The pathogenetic mechanism of the affection is mechanical, pharmacological, and allergic in nature. Besides skin, T. pityocampa Schiff can involve the eyes and rarely the airways. Despite the considerable damages to humans and nature, pine caterpillar infestation is an underestimated problem; medical literature lists few studies, and often relevant information is referred to local media and popular wisdom.

[Skin reactions on exposure to the pine processionary caterpillar (Thaumetopoea pityocampa)]

The pine processionary caterpillar is the larval form of the Thaumetopoea pityocampa moth. Mediterranean forests regularly suffer plagues of this insect, which has been moving north as a result of global warming. When the small urticating hairs that develop during the last 3 larval stages are shed and can become airborne. If they come in contact with skin, they can cause a variety of reactions, notably contact urticaria and papular rashes. Irritation can also occur if the hairs lodge in the mucosa of the conjunctiva or in the respiratory tract. Several cases of anaphylactic reactions have been reported in recent years. Mechanical (irritative) mechanisms may be involved in the pathogenesis of lesions, or immunoglobulin E-mediated allergic hypersensitivity reactions may be implicated when the process is rapid, recurrent, and progressively more severe.

Urticating hairs in arthropods: their nature and medical significance

The ecological phenomenon of arthropods with defensive hairs is widespread. These urticating hairs can be divided into three categories: true setae, which are detachable hairs in Lepidoptera and in New World tarantula spiders; modified setae, which are stiff hairs in lepidopteran larvae; and spines, which are complex and secretion-filled structures in lepidopteran larvae. This review focuses on the true setae because their high density on a large number of common arthropod species has great implications for human and animal health. Morphology and function, interactions with human tissues, epidemiology, and medical impact, including inflammation and allergy in relation to true setae, are addressed. Because data from epidemiological and other clinical studies are ambiguous with regard to frequencies of setae-caused allergic reactions, other mechanisms for setae-mediated disease are suggested. Finally, we briefly discuss current evidence for the adaptive and ecological significance of true setae.