06 Jan Spiders Are Rarely The Source Of Bacterial Infections

MedicalResearch.com Interview with:
Rick Vetter   (retired)
Department of Entomology
Univ. Calif. Riverside
Riverside, CA  92521

Medical Research: What is the background for this study? What are the main findings?

Response: Regarding the spider toxinology field, many misconceptions have been voiced over the years with statements being made in the medical literature which are tenable sounding explanations offered by well-meaning physicians, however, when given further scrutiny, are not supported by the data.  An example of this is the platitude from years ago (and sometimes still today) that brown recluse spider bites are feasible diagnoses anywhere in North America because the spiders CAN get transported around.  However, these authors never actually show that brown recluse spiders ARE frequently transported around in sufficient numbers such that they are tenable culprits in necrotic skin lesions.

The evidence developed in the last decade regarding this situation shows that brown recluses DO NOT get transported often, DO NOT establish extra-indigenous populations often and they are not likely etiologies for necrotic skin lesions outside of their indigenous range.  Similarly, a commonly heard statement over the decades is that spiders are likely vectors of bacterial skin lesions.  Several studies have swabbed the fangs and mouthparts of spiders, found bacteria and proudly proclaim the association between spider bites and bacterial infections.  However, these same authors never actually prove that verified spider bites result in bacterial transfer to humans.

This current study was instigated in part due to statements made in the 1990s by the late Dr. Philip Anderson, Missouri dermatologist and brown recluse spider bite expert, that recluse spider bites are never infected even in non-medicated patients.  So if spiders actually can vector bacteria, then a data-mining of the vast literature on spider bites worldwide should show significant bacteria association in the form of infected skin lesions as signs of envenomation.  In contrast, there is almost a complete absence of reports of infection when one examines the thousands of spider bites that include a vast array of medically important spiders including the widows, recluses, armed or wandering spiders of South America, Sydney funnel web spiders, wolf spiders, yellow sac spiders, as well as studies involving a random conglomeration of species.  A mechanism to explain this lack of bacterial vectoring may lie in the fact that the venom of spiders (as well as other venomous animals) has antibacterial and antimicrobial capabilities which may function evolutionarily to prevent bacterial transfer from prey to spider in bites.

Medical Research: What should clinicians and patients take away from your report?

Response: For clinicians and patients, the main take-home lesson is to stop relying on spiders as the scapegoats of bacterial infections.  In my many years of working with medically important spiders, I have heard many cases of patients being diagnosed as having spider bites and being given antibiotics.  Although this may seem to be a worthwhile prophylactic measure, antibiotics obviously do nothing to counteract the effects of venom.  What may be most frequent is that an infection is misdiagnosed as a spider bite then antibiotics are administered which remedies the infection, no matter what the etiology.  However, by diagnosing a spider bite, it conveys to the patient that this etiology is a valid one which, once a patient leaves the physician’s care, may evolve into the development of severe arachnophobia in the patient and his/her family to the point where psychological desensitization must be implemented and/or the overzealous abuse of dangerous pesticides by the patient in their living space due to the misconception that their medical malady has been caused by an arachnid.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: Future research would benefit with studies of verified spider bites to more securely document the lack of infection.  The current study was retrospectively examining a lack of the presence of bacterial infection in spider bites which is a somewhat non-definitive assessment.  It would be much better to prospectively corroborate this premise with a study where, when having the patient in treatment, one could look for the presence or absence of infection and document this information.

Citation:

Do spiders vector bacteria during bites? The evidence indicates otherwise
Vetter RS, Swanson DL, Weinstein SA, White J
Toxicon. 2015 Jan;93:171-4. doi: 10.1016/j.toxicon.2014.11.229. Epub 2014 Nov 21.

For more information:

1. Vetter-related websites for BROWN RECL– USE SPIDER INFO:  http://spiders.ucr.edu
2. Brown WIDOW ID guide    http://cisr.ucr.edu/identifying_brown_widow_spiders.html
3. hobo spider ID guide   pep.wsu.edu/pdf/PLS116_1.pdf
4. Check out the “Spider Myths Web Site”!
   http://www.washington.edu/burkemuseum/spidermyth/index.html

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Last Updated on January 6, 2015 by Marie Benz MD FAAD