Tuesday, August 17, 2010

Do Whitetail Spiders Cause 'Flesh Eating' Ulcers?

There is a change in the reporting of stories about whitetail spiders in the media and among professionals. The direction the media is now taking is that whitetail spiders are not a threat and those that continue the promotion of the ‘danger’ of white tails and necrotic arachnidism (ulceration due to spider toxins) are scare mongers.

I have a personal view that there is ‘something’ to the reports of ulcers caused by white tail bites. The reports in medical journals and from universities, hospitals, etc. stating that there is no evidence for ulcers being caused by whitetail bites, all fail to discuss the possibility of bite infection carried by the spider rather than the spider toxin causing the ulceration. The evidence they use is collected from hospital records of admissions for spider bites or for ulceration. They have not found that those with confirmed whitetail bites show ulceration, but this is not surprising if it is caused by infection as the hospital would administer antibiotics as a matter of course.

In the cases of ulceration they have not identified an infection, again because antibiotics would be administered and also because the causative agent may be difficult to culture. My own work on mycobacteria included culturing and identifying Mycobacterium ulcerans which as you might guess from its name causes just the sort of ulceration seen with the reported spider bites. The culturing and identification of this organism is notoriously difficult even for reference labs. It is even unlikely that hospitals would attempt it. If M. ulcerans is the cause of these ulcers then I would expect significant under reporting.

M. ulcerans is, in my opinion, a prime suspect in the identification of the cause of ulceration attributed to whitetail spiders. M. ulcerans is a common soil bacterium and could easily be picked up by whitetails. Whitetail spiders actively hunt and predate other spiders specially the grey house spider. Both the whitetail and the grey house spider are normally found on the ground in soil and leaf litter.

The jury is still out on the whitetail spider but I know I will be protecting myself, even if it is just from a painful bite, by spider proofing my house soon.

What do you call a big Irish spider?
Paddy Long Legs.

1 comment:

  1. I've just been reading the study by Pincus 1999. It seems that there is fair evidence that white tailed spider bytes can cause severe ulcerations, but so can the common house spider (Badumna). The cases he lists suggest that there are at least 3 species that can do this in rare cases. The Isbister and Gray study shows that the two common White Tail species cause no ulceration, but they were all from inside the house. Species encountered in the garden may be different. If ulceration was caused by bacteria, antibiotic treatment would tend to always clear the ulcers, and they would not recur.

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