Spiders or Scapegoats, necrotising skin ulcers cannot be solely attributable to spider bites

Main Category: Public Health
Article Date: 06 Aug 2004 - 12:00 PDT

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A viewpoint article in this week's issue of THE LANCET (pp 484, 549) discusses how the negative portrayal of spiders through the centuries is largely unfounded, and that necrotising skin ulcers in particular cannot be solely attributable to spider bites.

Author Geoffrey Isbister (Newcastle Mater Misericordiae Hospital, Australia) comments: "Putting aside emotion and dislike for these creatures, and based on a rational assessment of the risks, the fear or concern about spiders is unfounded. Most spiders do not pose a medical risk. Even spiders that can cause clinically significant human envenoming cause very little mortality or severe morbidity.

Scorpions are responsible for a far greater burden of illness worldwide. In Australia and the USA, bee and wasp stings account for many more deaths than spider bites. Spiders can also be compared with cars.

The fear of cars is rare, and there are few myths about the medical effects of car travel even though more deaths occur from motor vehicle accidents each year than from spider bites, and people take a great risk every time they travel in a car.

In 2001, there were 1183 motor vehicle deaths involving drivers or passengers in Australia, but no deaths from spider bites."

Various models to explain spider phobia are detailed: the 'non-associative' model, where fear is not based on previous negative experience, but rather on an innate Darwinian concern that spiders are venomous; another model suggests that spider phobia depends on conditioning, modelling, and negative information experiences; the 'disgust sensitivity' theory proposes that people who are scared of spiders also have a fear of other animals that evoke disgust such as slugs and maggots; this final theory provides some explanation for the association of spiders with disease.

There are many misconceptions surrounding spiders and disease-from them being the alleged causes of the great plagues to the cause of skin ulcers. Dr Isbister comments: "The current myth asserts that many types of spider are responsible for necrotic ulcers. This is a perception of both patients and medical practitioners.

Despite significant advances in the biomedical sciences and increasing focus on evidence-based medicine, the diagnosis of a spider bite continues to be based mainly on suspicion and fear of spiders, and diagnosis of a chronic ulcer on stories of suspected spider bites causing devastating necrotic fasciitis (flesh-eating skin disease)."

An accompanying commentary (p 484) by Richard Vetter (University of California, USA) agrees that the medical community has helped weave a web of misinformation about the alleged dangers of spiders.

He concludes: "Instead of using the presumptive diagnosis of spider bite when the causative agent is unknown, physicians should diagnose idiopathic [of unknown cause] necrotic ulcer, which accurately describes the clinical presentation of the lesion. Some medical conditions confused with necrotic spider envenomation can result in far worse outcome than most spider bites. The worldwide medical community would do well to relegate spider bite to the bottom of the list of differential diagnoses and consider the plethora of other conditions that manifest in dermonecrosis which have higher probability of occurrence than the rare necrotic spider envenomation".

http://www.thelancet.com

Contact: Dr Geoffrey K Isbister, Clinical Envenoming Research Group, Newcastle Mater Misericordiae Hospital, Waratah NSW 2298, Australia; T) +61 (0)2 4921 1211 or +61 (0)438 466 471; gsbite@ferntree.com

Dr Richard S Vetter, Department of Entomology, University of California, Riverside, CA 92507 USA; and Biology Division, San Bernardino County Museum, Redlands, CA 92374 USA; T) +1 909 787 3550; rick.vetter@ucr.edu)

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