Necrotic Arachnidism

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Necrotic arachnidism in Missouri is strikingly similar to “gangrenous spot” or cutaneous arachnidism of South America caused by Loxosceles laeta. A typical case report presents a distinctive clinical picture quite unlike that due to a black widow bite. Severe pain develops at the site of the bite and within the next 24 to 36 hours a systemic response is likely to occur, characterized by restlessness, fever, and at times the development of a generalized scarlatiniform eruption. Locally an ischemic area develops, surrounded by redness and extravasated blood, and becoming rapidly neerotic, with a central sloughing area which forms a deep ulcer exposing at times the underlying muscles. Slow gradual evolution with scarring follows. Experiments with Loxosceles reclusus, the probable agent of necrotic arachnidism in Missouri, and laboratory animals showed that the spider produces a powerful necrotoxin which it can readily inject into the skin of mammals, producing in the guinea pig tissue damage characterized by local hemorrhage, acute inflammatory cell reaction and, within three or four days, liquefaction with the formation of an abscess resulting in granulation and scarring. There is some species variation, rabbits being more susceptible than guinea pigs. The venom of both sexes of L. reclusus was found to be toxic. Rabbits were immunized after four bites or injections of venom. L. reclusus has been collected readily from the homes of patients with “brown spider bite” and appears to be a common house spider in Missouri.

Author Notes

Department of Pathology, School of Medicine, University of Missouri. Deceased Dec. 9, 1956.

Department of Entomology, College of Agriculture, University of Missouri.

Department of Medicine, Jefferson Medical College of Philadelphia.

Department of Pathology, School of Medicine, University of Missouri.