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Brown Recluse Spider Bite

The brown recluse spider, Loxosceles reclusa, is widely distributed in the United States throughout the Southeast and Midwest. Its natural habitat is outdoors under overhanging rocks and cliffs; it also lives in closets, attics, and outbuildings. The brown recluse hibernates during the winter; most bites occur between March and October.

Responses to bites range from mild local urticarial (hive-like) reactions to full-thickness skin necrosis. The more extensive reactions may be associated with systemic manifestations including a maculopapular rash, fever, headache, malaise, joint aches, and nausea and vomiting. The bite itself is generally painless, and the findings of a central papule and associated redness may not be seen for 6 to 12 hours. Only approximately 10% of bites progress to skin necrosis; those that do tend to show progression in 48 to 72 hours. Central blistering with a surrounding gray to purple discoloration at the bite site may appear. The site is surrounded by a ring of blanched skin that in turn is surrounded by a large area of redness, producing the "red, white, and blue" sign typical of a brown recluse spider bite. At this stage, the bite is associated with significant pain. As the wound becomes necrotic, it will turn black. Healing is slow and may require skin grafting to cover the defect.

Not all victims recall the spider bite, and because the clinical appearance is nonspecific, diagnosis can be difficult.

Differential Diagnosis: Brown recluse spider bites can be distinguished from cutaneous anthrax in the following manner.

Brown recluse spider bite


Cutaneous anthrax

*Patient has a possible history of spider bite or recent exposure to spider habitat

*Bite lesion becomes painful

*Lesion may manifest the red, white and blue sign


* Lesion is painless

* Ulcer and eschar are surrounded by characteristic non-pitting edema



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