A reduced immunization scheme to obtain an experimental anti-Loxosceles laeta ("violinist spider") venom

Bites by Loxosceles (L.) laeta spiders can produce severe envenomation in humans. The only specific treatment is the early administration of antivenom. The production of anti-Loxosceles antivenom is hampered by the extremely low venom yield by these spiders and by the difficulties in maintaining a large breeder of Loxosceles. We developed an experimental equinum L. laeta antivenom, using as immunogen venom glands homogenates from spiders captured in Argentina. Horses immunized with venom gland homogenate (1.0 mg total protein per horse) by the subcutaneous route were bled after completion of the immunization scheme. Plasma was fractionated by ammonium sulfate precipitation and treated with pepsin to obtain F(ab')2 fragments. The protein composition of the experimental antivenom was assessed by SDS-PAGE, and its immunochemical reactivity was compared with those of other anti-Loxosceles antivenoms available for therapeutic use in Argentina by ELISA and Western blot. The experimental, homologous anti-L. laeta antivenom appeared to be more efficient in neutralizing the lethal potency in mice and the necrotizing activity in rabbits than of the heterologous antivenom.