Dermatitis linearis outbreak associated with Paederus balcanicus in Austria

Rove beetles (family Staphylinidae) represent one of the largest groups of beetles with more than 50,000 known species worldwide. Paederus is a genus consisting of more than 500 species within this family. Paederus beetles are relatively slender and small (approximately 1.5 mm wide and 7–10 mm long) and easily recognized by the characteristic coloring (black head with red or orange thorax). They inhabit moist areas, such as marshes and edges of freshwater lakes and are active during the day but are also attracted to incandescent and fluorescent light at night. Paederus beetles are predators of other insects and nematodes and in some agricultural areas are considered as helpful in the biological control of crop pests; however, local Paederus invasion and proliferation associated with anthropogenic and landscape disturbances has become an issue in some urban settings, particularly in Africa and Southeast Asia [1].

At least 20 species within the genus Paederus cause characteristic skin lesions on contact. These injuries are caused by the vesicant toxin pederin, which is present in the hemolymph of female beetles [2]. Pederin is an amide with two tetrahydropyran rings produced by endosymbiotic Pseudomonas bacteria and prevents cell division, inhibits protein and DNA synthesis. It is among the most potent known non-proteinaceous toxins. Paederus beetles do not bite or sting, but the toxin is typically released when the beetles are crushed while being brushed away, thus causing characteristic linear skin irritations (dermatitis linearis or whiplash dermatitis). Interestingly, initial skin contact with pederin causes no injury, but lesions emerge later within 12–36 h after contact. Toxic hemolymph present at a primary site may be transferred to a secondary site by touch, thus causing characteristic kissing or mirror lesions. Treatment of Paederus lesions is ill-defined, but washing of exposed skin areas with water and soap and application of (topical) steroids and antihistamines are commonly recommended [1, 3]. The use of oral antibiotics is recommended to prevent or treat secondary infections [4, 5] but has also been reported to reduce healing time of dermatitis linearis in general [6]. Lesions usually resolve within days to weeks but may leave behind scarring and hyperpigmentation. In the eye, pederin may cause severe conjunctivitis that may lead to blindness (Nairobi eye).

Dermatitis linearis outbreaks have been described mainly in local populations in tropical and subtropical regions and in travellers [3]; however, invasion of Paederus spp. into human settings, potentially associated with climate change, is an emerging public health concern throughout the world. In Europe, dermatitis linearis outbreaks have so far been described anecdotally in Italy and were associated with P. fuscipes [7].

Similar to other insects causing skin lesions, Paederus species have recurrently been linked to human injury including local mass breeding forcing the evacuation of entire communities [2, 10]. We describe here our observation of a cluster of persons with skin injury associated with a Paederus species in Austria. While the cluster was confined to a relatively small group of seven persons in this case, it highlights that raising awareness and planning of adequate measures for prevention of further and larger outbreaks of Paederus-associated disease are warranted in Central Europe.

We identified Paederus balcanicus as a potential cause of dermatitis linearis using morphological and molecular techniques. Although we did not demonstrate pederin in the hemolymph of the collected beetles, we consider the circumstantial evidence presented here as highly indicative of a relevant medical role of P. balcanicus. Our finding is of interest, as P. balcanicus has not been recognized as one of the toxic Paederus species so far. Little is known about this species and only few publications are available, but it has been described as stenotopic (occurring only in one or a few habitats), hygrophilous (preferring moist habitats), and paludicolous (marsh-dwelling) [11, 12]. The first observation of P. balcanicus in the Austrian Lake Neusiedl area dates back to 1957, when Scheerpeltz described collected rove beetles as P. trapeziceps, which turned out to be a synonym of P. balcanicus [13]. More recently, the occurrence of P. balcanicus in two other Austrian locations has been documented [11, 14]. Further systematic investigations are needed to better understand the biology, life cycle, behavior and distribution of Paederus balcanicus.

Females of the genus Paederus have been reported to use the toxin pederin to chemically defend themselves, their eggs and their offspring against predators [15]. Beyond that, this toxin was found to exhibit potent antitumor activity caused by selective inhibition of the eukaryotic ribosome [16]. In cytotoxicity assays using human carcinoma cell lines, IC₅₀ values in the subnanomolar range were observed [17]. In the beginning, studies of the anticancer effect of pederin have been hampered by the fact that the true producer of pederin, a bacterial endosymbiont of Paederus beetles, is not culturable in a laboratory setting. Recently, however, the successful chemical synthesis not only of pederin itself but also of related molecules enabled the exploration of the potential of this promising family of anticancer drug candidates [18].

A number of measures to prevent linear dermatitis associated with Paederus species have been proposed. The most important actions are awareness-building measures in regions with resident occurrence of Paederus such as distribution of information on looks and behavior of the beetles, the importance of avoiding fluorescent lights to prevent attraction of the beetles at night, the correct removal of beetles from the skin to prevent toxin release, and the correct treatment of skin lesions [5]. In our case, the authors recommend the instalment of information and warning signs in the affected public recreational area of Lake Neusiedl.

In conclusion, we report for the first time (a) an outbreak of dermatitis linearis associated with exposure to an autochthonous Paederus species in Austria, and (b) that contact to the species Paederus balcanicus may be a cause of dermatitis linearis in humans. We consider dermatitis linearis outbreaks due to Paederus occurrence an emerging public health concern.