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Spider bites 'scapegoat' for cutaneous bacterial infection
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There is little evidence of a causative association between spider bites and bacterial infections, according to recently published data.
Richard S. Vetter, MS, formerly of the department of entomology at the University of California, Riverside, and colleagues reviewed studies on spider envenomations to determine whether or not spiders are vectors for bacterial infections. In a letter to the editor in Toxicon, their findings indicated little relation between the two.
“Although spider bite may be an attractive and tenable causative agent of a bacterial infection, this etiology is highly improbable,” the researchers wrote. “We believe any implied causative association between cutaneous infections and spider bites should be considered suspect, and that the medical community should not rely on spiders as the scapegoats for bacterial infections.”
Widow spiders, recluse spiders, Brazilian wandering or armed spiders, and Australian funnel web spiders were among those included in the reviewed studies. Infection was found to be either extremely uncommon or nonexistent, with some studies acknowledging the possibility that infection could have resulted from another source. Only one report — an Australian golden silk spider bite that led to Photorhabdus luminescens colonization — was deemed a credible example of documented infection.
“Patients may offer histories of antecedent trauma to the skin as the source, but often there is no obvious cause,” the researchers wrote. “If infection were part of spider bite syndrome, it should be obvious, common and a routinely reported manifestation of envenomation.”
The researchers wrote that a clear distinction exists between the infusion of venom through a spider bite and a contaminated break in the skin. Although some studies found that bacteria could be present on fangs or other mouthparts, such cases were unlikely and often negated by the spider’s venom.
“In fact, spider venoms are known to have antibacterial properties and were subject to investigation in hope of discovering novel antibacterial therapeutics,” the researchers wrote.
Despite this, cited studies demonstrated that many patients presenting for spider bites were diagnosed with cutaneous infections (85.7%) as opposed to envenomation (3.8%), and that 29% of patients with confirmed etiologies of MRSA had originally presented for spider bites. These mistakes, the researchers wrote, are not exclusive to patients.
“ ‘Spider bite’ is used as a default diagnosis despite lack of supporting evidence,” the researchers wrote. “Placing blame on spiders as the etiology for idiopathic wounds reinforces a prejudice that can have unwarranted post-incident fallout once a patient leaves the physician’s care.
“It appears that the often-errantly assigned spider-bacteria connection is yet another myth.”
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Arnon Shimshony, DVM
Community-associated MRSA has been recorded since the late 1990s, mainly as skin and soft-tissue infection and has become widely distributed since. The presentation of CA-MRSA skin infection, particularly in an early stage, resembles few other lesions, including spider bites. In view of the common tendency of patients and — when children are concerned — their parents to attribute suddenly appearing, insect-bite-like skin lesions to spiders, the critical differentiation of the two conditions, securing the correct, specific treatment and medication, becomes essential.
The reviewers have derived their data from 25 references, published between 1935 and 2006, most of them (n=20) addressing spider bites in Australia, the United States and Brazil; the others are from Europe (n=2), Asia (n=2) and South Africa (n=1). These studies, and the combined experience and academic background of the reviewers (entomology, dermatology, toxicology, family medicine), provide solid basis for their conclusion, assigning a spider-bacteria connection as unlikely. Spiders are not to be counted among the arthropods regarded as disease vectors, such as mosquitoes, ticks, sandflies, lice, fleas, mites, midges (Culicoides) and black flies. This review is a valid reminder for GPs, pediatricians and dermatologists.
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