Characterization of the venom from the Brazilian Brown Spider Loxosceles similis Moenkhaus, 1898 (Araneae, Sicariidae).

Accidents caused by brown spiders (Loxosceles genus) are frequent in Brazil and are associated with dermonecrotic lesions and, eventually, systemic reactions that may be lethal. The major species implicated with human envenoming have been: L. intermedia, L. gaucho and L. laeta. In this study we characterized the venom from Loxosceles similis, a species of spider normally found inside caves. L. similis venom was characterized by two-dimensional gel electrophoresis and enzymatic activity (dermonecrosis and haemolysis). The lethal dose to mice and the capacity of commercial anti-serum to neutralize this venom were also analysed. The cross-reactivity with anti-venoms against L. intermedia, L. laeta and L. gaucho were studied. Our results showed that this venom was able to induce severe dermonecrotic lesions and showed the presence of the bacteria Clostridium septicum in association with the fangs. In addition, we have cloned the DNA coding for a dermonecrotic protein (LsD1), using the genomic DNA of L. similis. The deduced amino acid sequence showed a toxin of approximately 31.2 kDa with an estimated pI of 7.37 and sequence similar to LiD1, a protein from the dermonecrotic family of Loxosceles intermedia spider venom, a synanthropic species of medical importance.

Development and evaluation of the neutralizing capacity of horse antivenom against the Brazilian spider Loxosceles intermedia.

Spider bites due to Loxosceles intermedia are currently a major public health problem in South Brazil. About 3000 cases are reported annually. Specific treatment for spider bites is provided by the polyvalent anti-arachnidic antiserum produced by Butantan Institute, São Paulo, Brazil by immunizing horses with mixtures of venoms from Tityus serrulatus and T. bahiensis scorpions, as well as Phoneutria nigriventer and L. gaucho spiders. Due to the large amounts of the anti-arachnidic antivenom required and since L. intermedia venom has some biochemical and pharmacological variations, we have produced a specific anti-L. intermedia antivenom. This study shows that horses immunized with crude L. intermedia venom produced IgG antibodies that neutralized the dermonecrotic and lethal activities of the venom. The neutralizing potency of the anti-loxoscelic antivenom was compared with that of the anti-arachnidic antivenom. Our results indicate that both antivenoms were effective in terms of neutralization. However, the anti-loxoscelic antivenom was more efficient than the anti-arachnidic.

ELISA for the detection of venom antigens in experimental and clinical envenoming by Loxosceles intermedia spiders.

Enzyme linked immunosorbent assays (ELISA) were developed to detect antigens from Loxosceles intermedia spider venom. Hyperimmune horse anti-Loxosceles intermedia IgGs were prepared by immunoaffinity chromatography and used to set up a sandwich-type ELISA. The specificity of the assay was demonstrated by its capacity to correctly discriminate the circulating antigens in mice that were experimentally inoculated with L. intermedia venom from those inoculated with L. gaucho, L. laeta, and Phoneutria nigriventer spider venoms, Tityus serrulatus scorpion venom and Bothrops jararaca, Crotalus durissus terrificus, Lachesis muta muta and Micrurus frontalis snake venoms. Measurable absorbance signals were obtained with 0.8 ng of venom per assay. The ELISA also detected antigens in the sera of patients envenomed by L. intermedia. Therefore, after standardization for clinical use this ELISA may be a valuable tool for clinicians and epidemiologists.