Intradermal anti-loxosceles fab fragments attenuate dermonecrotic arachnidism

Objective: Bites from the brown recluse spider and other arachnids from the genus Loxosceles frequently induce necrotic skin lesions that can be recal citrant to treatment and disfiguring. The authors used a rabbit model of de rmonecrotic arachnidism to address the therapeutic efficacy of intradermal (id) polyclonal anti-Loxosceles Fab fragments (alpha Loxd Fab) raised again st Loxosceles deserta spider venom. Methods: Fab fragments were prepared by papain digestion and affinity chromatography from the Ige fraction oft. de serta antivenom raised in rabbits. Eighteen inbred New Zealand white rabbit s were:assigned to six groups of three. The rabbits received L. deserta ven om (3 mu g, id) injections into each flank. Cohorts of rabbits received sin gle id injections (at one venom site/rabbit) of 30 mu g alpha Loxd Fab at d ifferent times (T = 0, 1, 2, 4, 8, and 12 hours) after venom injection. In each rabbit the opposite flank was left untreated. As an additional control , one group of rabbits (T = 0) received nonspecific Fab (30 mu g, id) in th e opposite flank. Dermal lesions were quantified as a function of time thro ugh the use of a series of digital photographs and imaging software. In add ition, myeloperoxidase (MPO) activity, a measure of neutrophil accumulation , was determined in lesion biopsies. Lesion areas and MPO activities were a nalyzed by repeated-measures analysis of variance (ANOVA). Results: Lesion areas and MPO activity were markedly reduced when alpha Loxd Fab was admini stered very early after venom injections. As the interval between venom ino culation and antivenom treatment increased, the therapeutic benefit of alph a Loxd Fab decreased. The final time tested that demonstrated therapeutic e fficacy of alpha Loxd Fab was T = 4 hours. Lesion attenuation was no longer apparent when alpha Loxd Fab was given 8 hours post inoculation. Conclusio ns: Intradermal administration of alpha Loxd Fab attenuates Loxosceles-indu ced dermonecrotic lesion formation when given up to 4 hours after venom ino culation:in this rabbit model.