Overdiagnoses of Brown Recluse Spider Bites


The misdiagnoses of spider bites by both the general public and the medical community are a significant problem in North America.  In particular, the brown recluse, Loxosceles reclusa, is falsely blamed for numerous dermonecrotic lesions including diabetic ulcers, lyme disease, and most medically significant, methicillin-resistant Staphylococcus aureus (MRSA).  In one study conducted in South Carolina, the number of diagnosed L. reclusa envenomations (loxoscelism) significantly outweighed the understood population of the species. [1]


The study revealed that in 1990, 478 bites were reported with only 42% of physicians responding to the survey.  The number of reported bites rose to 738 in a 2004 survey while the number of physicians responding dropped to 19%.  The study added that only 44 specimens of L. reclusa have ever been officially documented within the state. 

Another study surveyed four western states (California, Washington, Oregon, and Colorado) that lack established populations of L. reclusa, yet reported 216 cases of loxoscelism over a forty-one month period. It is important to note that three of the outcomes of the 216 cases resulted in an amputation, a double amputation, and one death. [2] The lack of verified L. reclusa populations in the region suggests that a different pathology was responsible and further demonstrates the necessity for a proper diagnosis.

In regards to the spider itself, there is great ignorance to its distribution and its proper identification.  Many people, including doctors and zoologists, believe L. reclusa to be cosmopolitan, while it is actually contained within the south east/central portion of the United States.  As L. reclusa is a small, brown spider, it is commonly misidentified with hundreds of similar small, brown spiders. 

  [1] Frithsen, I.L., Vetter, R.S., and Stocks, I.C.  2007.  Reports of Envenomation by Brown Recluse Spiders Exceed Verified Specimens of Loxosceles Spiders in South Carolina.  The Journal of the American Board of Family Medicine 20(5): 483-488.
  [2] Vetter, R.S., Cushing, P.E., Crawford, R.L., and Royce, L.A., 2003.  Diagnoses of brown recluse spider bites (loxoscelism) greatly outnumber actual verifications of the spider in four western American states.  Toxicon 42:413-418.
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