Thank Christ someone chimed in with the facts eventually in this thread
! In Australia the media has ‘beat up’ the myth that white-tail bites
cause necrotising arachnidism. Nice work Lara, you rock !
The study published last year that Lara alludes to by Isbister and Gray
is the most powerful and convincing evidence to date that white-tails
don’t cause necrotising arachnidism. They only included patients that
had captured the spider that bit them on the spot, and they had all
spiders identified ‘in the flesh’ by experts. Impressively, and
relevant to Paul’s post (above) suggesting that there could be an odd
species distribution accounting for anecdotal reports of white-tail
induced ulceration, they went as far as identifying all ‘white-tips’
(Different Lampona genus spiders) down to the species level.
130 certified white-tail bites, zero necrotic lesions. Relevant to the
above post from “ax”, they also confirmed zero infections.
http://tinyurl.com/43bxw

There is another interesting study relevant to Isbister and Gray’s
final conclusion (see Lara’s post, directly above), particularly their
assertion that “Previously we have shown that there were no necrotic
lesions when all spider types in Australia were analysed. These data
suggest that spiders are an extremely uncommon cause of necrotic or
cytotoxic lesions, and should be considered only at the end of a long
list of other differential diagnoses”

This seems to amount to a tactfully phrased (but wise) suggestion that
when patients present with necrotic lesions that they think were caused
by a spider bite, they are most likely to be wrong (and inadvertently
misleading the physician to their own detriment).

One group has investigated this specific question scientifically, and
just published their results this year. Probably because white-tails
do not actually cause necrotic lesions, the sample size (the number of
people that actually presented with existing lesions that the patients
themselves believed were caused by white-tails) was small, 11. So the
study is nowhere near as powerful as Isbister and Gray’s. But like the
venom study alluded to by ‘Rod’ above, it is completely concordant with
their conclusions.
Physiologically verified alternative causes of ulceration ? All 11
patients. Their conclusion:
“In this series, all cases initially referred as WT spider bites or
necrotic arachnidism were found to have alternative diagnoses with
appropriate investigations. This demonstrates that spider bites are an
unlikely cause of necrotic ulcers and that all ulcers should be
properly investigated with bacterial, fungal and mycobacterial cultures
and skin biopsy for histopathology”.
http://tinyurl.com/5smqy

So why does the myth persist. ? In my humble opinion it is the product
of a combination of irresponsible media hype, and human psychology.
Applying principals of psychology, I think people would often feel
embarrassed when they develop necrotic skin lesions, because they’re
disfiguring and ugly. People are more comfortable believing that such
ailments are due to external causes, that are clearly ‘not their fault’,
rather than an internal deficiency or the like. I hope this suggestion
doesn’t offend anyone.
Cheers, Owen Proudfoot


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Owen Proudfoot