Reports of Envenomation by Brown Recluse Spiders Exceed Verified Specimens of Loxosceles Spiders in South Carolina

Ivar L. Frithsen, MD, MS; Richard S. Vetter, MS; Ian C. Stocks, MS

Disclosures

J Am Board Fam Med. 2007;20(5):483-488. 

In This Article

Abstract and Introduction

Abstract

Purpose: To determine whether the number of brown recluse spider bites diagnosed by South Carolina physicians coincides with evidence of brown recluse spiders found in the state.
Methods: Brown recluse spider bite diagnosis data were extracted from 1990 and 2004 surveys of South Carolina physicians. This was compared with the known historical evidence of brown recluse spiders collected in South Carolina and derived from various sources, including state agencies, arachnologists, and museum specimens.
Results: South Carolina physicians diagnosed 478 brown recluse spider bites in 1990 and 738 in 2004. Dating to 1953, 44 brown recluse spider specimens have been verified from 6 locations in South Carolina.
Discussion: The number of brown recluse bites reportedly diagnosed in South Carolina greatly outnumbers the verified brown recluse specimens that have been collected in the state. The pattern of bite diagnoses outnumbering verified brown recluse specimens has been reported in other areas outside of this spider's known endemic range.

Introduction

The range of the brown recluse spider, Loxosceles reclusa, is restricted to a specific portion of the southeastern and central United States, which potentially includes the westernmost tip of South Carolina[1] (Figure 1). Despite this limited distribution, necrotic skin lesions have been attributed to loxoscelism (bites by Loxosceles spiders) throughout the continental United States, Canada, and Alaska.[2,3,4] In many areas where bites by brown recluse spiders are commonly reported, verified specimens are rare, no current populations are known to exist, and, in some cases, no Loxosceles spiders have ever been found.[2,3,4,5] This disparity between large numbers of reported loxoscelism cases versus few verified brown recluse specimens in areas outside of their native range signifies that this condition is over diagnosed in many parts of the country.

Figure 1.

Geographic distribution throughout the United States of verified widespread populations of 6 native Loxosceles species. Reprinted with permission of the Massachusetts Medical Society.

There are many alternate causes of skin lesions that have been mistaken for brown recluse spider bites,[1] including methicillin-resistant Staphylococcus aureus (MRSA). MRSA is a rapidly emerging infectious disease threat in many parts of the United States.[6,7,8,9] A recent study of patients with skin and soft-tissue infections presenting to 11 different emergency departments noted that MRSA was isolated from 59% of patients. This led to the conclusion that MRSA is now the most common cause of skin and soft tissue infections in the cities studied.[10] The prevalence of MRSA was noted to be 68% in Charlotte, North Carolina, and 72% in Atlanta, Georgia, during August 2004.[10] Studies have shown that patients with MRSA infections frequently present to their physicians with a complaint of spider bite.[10,11] The severe pain often experienced by patients with MRSA skin infections is probably the reason they think they have been bitten by a spider.[12] Therefore, in areas where brown recluse bites are commonly diagnosed but brown recluse spiders are rare, it is likely that MRSA infections are being missed. This would be especially true where MRSA prevalence is known to be high, making it important to examine spider bite data in these areas.

Although there are no published reports indicating the prevalence of MRSA in South Carolina, based on the numbers noted above from neighboring states it is likely that MRSA infections are common in South Carolina. Another reason for studying this issue is that the westernmost tip of South Carolina is on or just beyond the natural range of the brown recluse spider. In addition, data concerning the number of physician-diagnosed brown recluse bites is available from surveys of South Carolina physicians that were conducted in 1990 and 2004.[13,14] Finally, there are several available sources for determining the distribution of brown recluse spiders in South Carolina, including accessible collections from national and state museums and information obtained from Clemson University entomologists. The objective of this study was therefore to determine whether the known distribution of brown recluse spiders in South Carolina corresponds to statewide reports of loxoscelism. Information compiled here would be useful for physicians anywhere outside of the endemic brown recluse range.

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