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Arthropod Bites or Stings
Published in Jerome Goddard, Public Health Entomology, 2022
Direct tissue damage from stings or bites may lead to development of skin lesions. Arthropod mouthparts puncture skin in various ways (through a siphoning tube, scissor-like blades, and so on), leading to skin damage; hence damage may be a small punctum, dual puncta (from fangs), or lacerations. However, most lesions result from host immune reactions to salivary secretions or venom. Arthropod saliva is important during feeding in order to lubricate the mouthparts on insertion, increase blood flow to the bite site, inhibit coagulation of host blood, anesthetize the bite site, suppress the host’s immune and inflammatory responses, and aid in digestion. In contrast, venom from certain spiders may directly cause tissue death (necrosis) in human skin. In the United States violin spiders (Figure 20.2D) are primarily responsible for necrotic skin lesions, although sac spiders (Cheiracanthium spp.) and hobo spiders are sometimes reported to cause necrotic arachnidism.17,18 Brown recluse spider venom contains a lipase enzyme, sphingomyelinase D, which is the primary necrotic agent involved in the formation of the typical lesions. Neutrophil chemotaxis may be induced by sphingomyelinase D. The influx of neutrophils into the area contributes to the formation of the necrotic lesion.
Principles of Treatment for Arthropod Bites, Stings, and Other Exposure
Published in Gail Miriam Moraru, Jerome Goddard, The Goddard Guide to Arthropods of Medical Importance, Seventh Edition, 2019
Gail Miriam Moraru, Jerome Goddard
In contrast to the widow spiders, violin spiders (brown recluse being one of the most notable) have venom that is necrotic in activity coupled with hyaluronidase which acts as a spreading factor. Brown recluse spider venom contains a lipase enzyme, sphingomyelinase D, which is significantly different from phospholipase A in bee and wasp venoms. This specific lipase is the primary necrotic agent involved in the formation of the typical lesions (see Chapter 29). It is possible that neutrophil chemotaxis is induced by sphingomyelinase D.14 The subsequent influx of neutrophils into the area is critical in the formation of the necrotic lesion.
Clinical Toxicology of Spider Bites
Published in Jürg Meier, Julian White, Handbook of: Clinical Toxicology of Animal Venoms and Poisons, 2017
Julian White, J.L. Cardoso, Hui Wen Fan
There have been a variety of studies of Loxosceles venom, but the exact mechanisms causing the local necrosis and systemic illness in man are still controversial. Given that the pathophysiology is poorly understood, several aspects have to be considered in understanding the mechanisms of action: Sphingomyelinase D is clearly an important component of Loxosceles venom,responsible, at least in part, for local skin necrosis, intravascular haemolysis and platelet aggregration23. A dermonecrotic fraction has been isolated from L gaucho venom, a common cause of loxoscelism in Brazil198.The role of polymorphonuclear leucocytes seems to be important in the development of local vasculitis, the putative cause of necrotic lesions. This led to new therapeutic approachs in loxoscelism36,199, using inhibitors of chemotaxis, which have proven beneficial clinically.The hemolytic activity may be related to G6PD deficiency200. Complement activation and other factors are apparently not involved.
How relevant are in vitro culture models for study of tick-pathogen interactions?
Published in Pathogens and Global Health, 2021
Cristiano Salata, Sara Moutailler, Houssam Attoui, Erich Zweygarth, Lygia Decker, Lesley Bell-Sakyi
In the context of virus–vector interactions, the role of the well-conserved I. scapularis organic anion transporting polypeptides (OATPs) was examined in ticks infected with LGTV [96]. While infection of unfed nymphal ticks with LGTV in vivo did not result in significant changes in oatps gene expression, specific genes were significantly downregulated upon LGTV infection of ISE6 cells in vitro. Treatment of tick cells with OATP inhibitor significantly reduced LGTV loads suggesting a role of arthropod OATPs in vector–virus interactions [96]. In the presence of LGTV, expression of arthropod IsSMase, a sphingomyelinase D that catalyzes the hydrolytic cleavage of substrates, such as sphingomyelin (SM) lipids, was significantly reduced in both I. scapularis ticks in vivo and ISE6 cells in vitro [97]. The LGTV-mediated suppression of IsSMase allowed accumulation of SM lipid levels supporting membrane-associated viral replication and exosome biogenesis, suggesting a role for arthropod IsSMase in tick-LGTV interactions and its function in vector defense mechanism(s) against TBV infection and in anti-viral pathways [97]. In vivo studies in ticks are required to confirm the roles of other antiviral responses, identified in studies focusing on flaviviruses in Ixodes spp. cell lines [98–100].
Atypical systemic and dermatologic loxoscelism in a non-endemic region of the USA
Published in Clinical Toxicology, 2021
John W. Downs, Kevin T. Gould, Ryan C. Mclaughlin, Kirk L. Cumpston, S. Rutherfoord Rose
Hemophagocytic lymphohistiocytosis (HLH) was described in a 10 year male after returning from summer camp in Tennessee [15]. It was presumed he was bitten by a LR because he presented one day after the bite with fever, pallor, jaundice, scleral icterus, anuria and a necrotic skin lesion. After meeting 7 of 8 criteria for HLH, he was started on hemodialysis and dexamethasone 10 mg/m2/day with rapid improvement. We did not assess all the criteria needed to diagnose HLH in our patient, and he most likely did not have secondary HLH. However, these authors illuminate the fact that sphingomyelinase D activates complement and stimulates pro-inflammatory cytokines, which could explain our patient’s SIRS presentation on day 7 post-bite. The benefit of therapeutic plasma exchange has been demonstrated in recent case reports [16,17], and direct and indirect antibodies to platelets have been found in LX [18]. These series of reports supports the hypothesis that the syndrome of LX is an immunological and inflammatory storm triggered by the venom that may manifest as hemolysis, acute renal injury and DIC, but also with alternative immunological and inflammatory effects [1,2].
Targeting Loxosceles spider Sphingomyelinase D with small-molecule inhibitors as a potential therapeutic approach for loxoscelism
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Priscila Hess Lopes, Mário T. Murakami, Fernanda C. V. Portaro, Kerly Fernanda Mesquita Pasqualoto, Carmen van den Berg, Denise V. Tambourgi
The recombinant Sphingomyelinase D (SMase D) from L. laeta venom was obtained as described by Fernandes-Pedrosa et al25. The protein content was determined using the method of Lowry et al26. The samples were stored at –80 °C until use.