Bacterial Etiology of Necrotic Arachnidism in Black Widow Spider Bites

Brad Ahrens

doi:10.4172/2161-0495.1000106

Abstract

Spider bites are a common challenge for physicians and veterinarians worldwide. Envenomation by the Western Black Widow (Latrodectus hesperus) is frequently associated with a necrotic cutaneous reaction at the bite site; a condition known as necrotic arachnidism. Although the composition of venom is known to be almost entirely neurotoxic, and thus, presumably not damaging to skin, varying degrees of dermal necrosis are commonly encountered at the site of envenomation. The underlying mechanism is unknown, prompting our investigation of the possibility for a bacterial etiology of the local lesions associated with the bite. This descriptive study reports the presence of 5 uncommon, highly pathogenic; multiple antibiotic resistant, bacterial species cultured from 220 pairs of sterilely extracted black widow spider fangs. This finding is consistent with the known unresponsiveness of cutaneous spider bite lesions to steroids and first-line antibiotic treatment; which has led to the misconception that the venom is the causative agent. This discovery supports our hypothesis that bacterial strains have adapted to life on the fangs of certain spiders; providing them with an excellent mode of infection by not only being passed subcutaneously to the victim, but also protected from host defenses by the immunosuppressive effects of the venom. Since current treatment protocols for spider envenomations concentrate almost solely on the local and systemic effects of the venom itself, our findings suggest that the current diagnostic algorithm and treatment standards for spider bites in both human and animal medicine may be inadequate and should be re-assessed.

Highlights

Spider bites meriting medical intervention on the west coast are surprisingly common
Since current treatment protocols for spider envenomations concentrate almost solely on the local and systemic effects of the venom itself, our findings suggest that the current diagnostic algorithm and treatment standards for spider bites in both human and animal medicine may be inadequate and should be re-assessed
The necrotizing lesions secondary to bites are often attributes to Morganella [22,23,24,25,26]. Capnocytophaga is another highly pathogenic bacteria which is most frequently found in dog bite wounds

Summary

Introduction

Spider bites meriting medical intervention on the west coast are surprisingly common. In 2008, there were over 12,500 reported bites on humans, with over 2,500 from widow spiders [1]. (The actual number of bites potentially being far greater because of lack of reporting) [2]. Spider bites are very difficult to treat for physicians, veterinarians, and patients. Diagnosis is a challenge because the spider culprit is rarely found or caught, and the bite produces a number of nonspecific signs with a long list of differentials. Black widows are members of the family Theridiidae (cobweb spiders). All species in the genus are medically important and bites result in a potentially fatal clinical syndrome known as latrodectism. The widows are responsible for killing more people per year, worldwide, than any other spider. The toxins are deposited in neuronal synapses and neuromuscular junctions and death is most commonly due to cardiovascular collapse or respiratory paralysis

Methods

Results

Conclusion