Cutaneous loxoscelism caused by Loxosceles similis venom and neutralization capacity of its specific antivenom

Abstract

Members of the spider genus Loxosceles pose a marked health risk to humans because of the seriousness of the necrotic and systemic effects of their bite, known as loxoscelism. The recent confirmation of Loxosceles similis in residences of Belo Horizonte in Minas Gerais Province, Brazil increases the local potential risk of loxoscelism at higher levels. The first characterization of the venom from this species showed that its main biological effects had a similar intensity as other species (e.g. Loxosceles intermedia, Loxosceles laeta, and Loxosceles gaucho). Therefore, we wished to further analyse the biological activity of the L. similis venom as well as the capacity of anti-L. similis-venom serum to reduce dermonecrotic effects to rabbit skin. Histological analysis of rabbit skin 2, 4 and 8h after intradermal injection of L. similis venom demonstrated a dense inflammatory infiltrate, edema, degeneration and necrosis of the skin muscle, dissociation of collagen fibers, and disruption of reticular fibers. Importantly, pre-incubation of the venom with anti-L. similis-venom serum significantly decreased all of these effects. Anti-L. similis antivenom generated antibodies that were strongly reactive to L. similis venom and capable of neutralizing the dermonecrotic effects in rabbits caused by this venom. Moreover, the antivenom significantly reduced the sphingomyelinase activity of L. similis crude venom. Venoms produced by male and female spiders were equally reactive towards anti-L. similis and anti-L. intermedia antivenoms, but female venom induced larger lesions on rabbits. In contrast, female venom acted as an immunization enhancer and protected animals from L. similis envenomation to a greater degree than male venom. In conclusion, the results shown in this study for L. similis antivenom merits a more in depth study of its properties, which may become a valuable tool against loxoscelism.

Histopathological characterization of experimentally induced cutaneous loxoscelism in rabbits inoculated with Loxosceles similis venom

“…According to our data, the inflammation increases progressively from two hours and then becomes severe eight hours post L. similis crude venom injection corroborating the already existing studies with L. laeta and L. intermedia venom (15,17,32). Morphometrical parameters showed here can be used to monitor the process dynamics, and also any treatment and sera effectiveness studies (22,31,33,34). In the present study, the heterophils/neutrophils were the predominant cells observed as mentioned by others for loxoscelism.…”

“…Macroscopically, the radius of the injured area increased over time as previously related in loxoscelism induced by other Loxosceles species (1,6,9). Notably, the venom concentration used in this work was very low (0.5 µg) compared with our previous study of 3 µg of venom, but it was enough to induce a very similar and severe lesion (22). Microscopically, a severe fibrinoushemorrhagic multi-focal acute dermatitis and a necrotic acute myositis were observed.…”

“…The venom used was extracted according to previous works and stored at -80°C (20)(21)(22). The protein content of the samples was determined by the Bradford method and confirmed by the Lowry method.…”

Successful Use of Plasma Exchange for Profound Hemolysis in a Child With Loxoscelism

“…[2][3][4][5][6] In almost all cases, supportive care with red blood cell (RBC) transfusions, intravenous fluids, and local wound care are sufficient to provide full recovery. 1,7,8 In more severe cases, hyperbaric oxygen, 9 dapsone, 10,11 and antivenom 12,13 have been used with variable success.…”

Whole venom of Loxosceles similis activates caspases-3, -6, -7, and -9 in human primary skin fibroblasts

“…Protein quantification was performed in the venom using the Bradford method (Bradford, 1976) with bovine serum albumin (BSA) (Sigma-Aldrich, CA, USA) as the protein standard. The absorbance was measured at 600 nm using an ELx 800 Universal Microplate Reader (Biotek Instruments, VT, USA) according to Chatzaki et al (2012).…”