Dermonecrotic Loxoscelism in the Mediterranean Region

Local Dermonecrosis with Generalized Urticaria Probably Due to Loxosceles rufescens Bite

BACKGROUND: The spiders of the Loxosceles genus, commonly denoted as “brown spiders” or “Mediterranean recluse” or “brown recluse,” belong to the spider family Sicariidae, suborder Labidognatha, order Araneida, class Arachnida, and phylum Arthropoda. This spider is widespread in Africa and South/Central America, but it is also distributed in North America, in the West Indies, in the Mediterranean Europe, and in China. CASE REPORT: Here, we report the case of a severe dermonecrotic loxoscelism identified in Southern Italy, probably due to the bite of Loxosceles rufescens. The patient was a women admitted at hospital ER because of a little skin erythema that evolved toward a severe necrosis and ulceration within 20 days. After clinical and laboratory data excluded other local and systemic diseases, she was treated with a systemic and local therapy using corticosteroids and antibiotics with the diagnosis of loxoscelism. The healing from the local skin lesion occurred within 2 months, but the local pain, weakness, and discomfort lasted for a long time. CONCLUSION: It is the fisrt time that a possible case of systemic loxoscelism with skin generalized urticaria is reported in Italy.

The kiss of (cell) death: can venom-induced immune response contribute to dermal necrosis following arthropod envenomations?

Introduction: Snakes, insects, arachnids and myriapods have been linked to necrosis following envenomation. However, the pathways involved in arthropod venom-induced necrosis remain a highly controversial topic among toxinologists, clinicians and the public. On the one hand, clinicians report on alleged envenomations based on symptoms and the victims' information. On the other hand, toxinologists and zoologists argue that symptoms are incompatible with the known venom activity of target species. This review draws from the literature on arthropod envenomations, snakebite, and inflammatory processes to suggest that envenomation by a range of organisms might trigger an intense inflammatory cascade that ultimately lead to necrosis. If confirmed, these processes would have important implications for the treatment of venom-induced necrosis. Objectives: To describe two inflammatory pathways of regulated necrosis, tumour necrosis factor (necroptosis) and Neutrophil Extracellular Traps (NETosis); to discuss existing knowledge about snake venom and arachnid-induced necrosis demonstrating the involvement of tumour necrosis factor and neutrophils in the development of tissue necrosis following envenomation and to contribute to the understanding of venom-induced necrosis by arthropods and provide clinicians with an insight into little known inflammatory processes which may occur post envenomation. Methods: ISI Web of Science databases were searched using the terms "spider bite necrosis", "arthropod envenomation necrosis", "venom necrosis", "venom immune response", "loxoscelism", "arachnidism", "necroptosis venom", "necroptosis dermatitis", "tumour necrosis factor TNF venom", "scorpionism", "scolopendrism", "centipede necrosis", "NETosis venom", "NETosis necrosis". Searches produced 1737 non-duplicate citations of which 74 were considered relevant to this manuscript. Non-peer-reviewed sources or absence of voucher material identifying the organism were excluded. What is necrosis? Necrosis is the breakdown of cell membrane integrity followed by inflowing extracellular fluid, organelle swelling and the release of proteolytic enzymes into the cytosol. Necrosis was historically considered an unregulated process; however, recent studies demonstrate that necrosis can also be a programmed event resulting from a controlled immune response (necroptosis). Tumour necrosis factor and the necroptosis pathway: Tumour necrosis factor is a pro-inflammatory cytokine involved in regulating immune response, inflammation and cell death/survival. The pro-inflammatory cytokine TNF-α participates in the development of necrosis after envenomation by vipers. Treatment with TNF-α-antibodies may significantly reduce the manifestation of necrosis. Neutrophil Extracellular Traps and the NETosis pathway: The process by which neutrophils discharge a mesh of DNA strands in the extracellular matrix to entangle ("trap") pathogens, preventing them from disseminating. Neutrophil Extracellular Traps have been recently described as important in venom-induced necrosis. Trapped venom accumulates at the bite site, resulting in significant localized necrosis. Arthropod venom driving necrosis: Insects, myriapods and arachnids can induce necrosis following envenomation. So far, the processes involved have only been investigated in two arachnids: Loxosceles spp. (recluse spiders) and Hemiscorpius lepturus (scorpion). Loxosceles venom contains phospholipases D which hydrolyse sphingomyelin, resulting in lysis of muscle fibers. Subsequently liberated ceramides act as intermediaries that regulate TNF-α and recruit neutrophils. Experiments show that immune-deficient mice injected with Loxosceles venom experience less venom-induced inflammatory response and survive longer than control mice. Necrosis following Hemiscorpius lepturus stings correlates with elevated concentrations of TNF-α. These observations suggest that necrosis may be indirectly triggered or worsened by pathways of regulated necrosis in addition to necrotic venom compounds. Conclusions: Envenomation often induce an intense inflammatory cascade, which under certain circumstances may produce necrotic lesions independently from direct venom activity. This could explain the inconsistent and circumstantial occurrence of necrosis following envenomation by a range of organisms. Future research should focus on identifying pathways to regulated necrosis following envenomation and determining more efficient ways to manage inflammation. We suggest that clinicians should consider the victim's immune response as an integral part of the envenomation syndrome.

Distribution and medical aspects of Loxosceles rufescens, one of the most invasive spiders of the world (Araneae: Sicariidae)

Loxosceles rufescens is a circum-Mediterranean spider species, potentially harmful to humans. Its native area covers the Mediterranean Basin and Near East. Easily spread with transported goods, it is meanwhile an alien and invasive species to nearly all other continents and many islands. This species occurs in semi-arid steppe-like habitats, typically under stones and in cavities, which enables it to settle inside buildings when invading the synanthropic environment. This review analyses the literature of L. rufescens bites to humans (38 publications) of which only 11 publications refer to 12 verified spider bites (11% of the reported bites). Two published allegedly deadly spider bites (Thailand 2014 and Italy 2016) involve non-verified spider bites and are thus not reliable. The symptoms and therapy of these 11 verified bites are described: only five cases showed moderate systemic effects, nine cases developed necrosis, four cases needed surgical debridement, all cases healed without complications within a few weeks. In conclusion, L. rufescens is a spider species globally spread by human activity, it rarely bites humans and the bites are less harmful than often described. There is no known fatal issue.

Not as docile as it looks? Loxosceles venom variation and loxoscelism in the Mediterranean Basin and the Canary Islands

The medical importance of Loxosceles spiders has promoted extensive research on different aspects of their venoms. Most of the reported cases of loxoscelism have occurred in the Americas, and thus, much work has focused on North and South American Loxosceles species. Interestingly, loxoscelism cases are rare in the Mediterranean Basin although Loxosceles rufescens, endemic to the Mediterranean, is an abundant spider even in human-altered areas. Thus, it has been suggested that the venom of L. rufescens could be of less medical relevance than that of its congeners. In this study, we challenge this hypothesis by using multiple approaches to study venom variation in selected species and lineages from the Mediterranean Basin and the Canary Islands. We found that SMase D activity, the key bioactive component of Loxosceles venom, is comparable to American species that are confirmed to have medically relevant bites. The venom protein composition using SDS-PAGE presents some differences among regional Loxosceles taxa in banding pattern and intensity, mostly between the Canarian and L. rufescens lineages. Differences between these species also exist in the expression of different paralogs of the SicTox gene family, with the Canarian species being less diverse. In conclusion, our results do not support the challenged hypothesis, and suggest that venom of these species may indeed be as potent as other Loxosceles species. Pending confirmation of loxoscelism with direct evidence of Loxosceles bites with species identification by professionals, Loxosceles in the Mediterranean region should conservatively be considered medically relevant taxa.

Immune-mediated mechanism for thrombocytopenia after Loxosceles spider bite

Loxoscelism, characterized by high fever, vomiting, malaise, a dermonecrotic lesion, and thrombocytopenia, was diagnosed in a 3-year-old female. Clinical laboratory and dermatological signs are described. Blood test showed a transient hypercoagulable state and the presence of IgG antibodies against platelets, suggesting an immune-mediated mechanism for platelet destruction, in addition to the direct toxic effect of the spider venom. The finding of platelet antibodies after a Loxosceles spider bite has not been previously reported.

Brown spiders and loxoscelism

Accidents caused by brown spiders (Loxosceles genus) are classically associated with dermonecrotic lesions and systemic manifestations including intravascular haemolysis, disseminated intravascular coagulation and acute renal failure. Systemic reactions occur in a minority of cases, but may be severe in some patients and occasionally fatal. The mechanisms by which Loxosceles venom exerts these noxious effects are currently under investigation. The venom contains several toxins, some of which have been well-characterised biochemically and biologically. The purpose of the present review is to describe some insights into loxoscelism obtained over the last ten years. The biology and epidemiology of the brown spider, the histopathology of envenomation and the immunogenicity of Loxosceles venom are reviewed, as are the clinical features, diagnosis and therapy of brown spider bites. The identification and characterisation of some toxins and the mechanism of induction of local and systemic lesions caused by brown spider venom are also discussed. Finally, the biotechnological application of some venom toxins are covered.