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REDBACK SPIDER BITE UNDERESTIMATED ... AND ANTIVENOM NOT EFFECTIVE
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The seriousness of bites by the redback spider in Australia has been
underestimated, according to a new study. Moreover, intramuscular antivenom is not as effective as previously thought.
Most people who have been bitten experience severe pain for over 24 hours.
The study, by Dr Geoffrey Isbister, from the Department of Clinical Pharmacology at the University of Newcastle, and Dr M R Gray, from the Australian Museum, was conducted prospectively from February 1999 to April 2002 from patients presenting to participating hospitals or contacting a poisons information centre.
Ninety-nine cases of bites by spiders of the family Theridiidae (comb-footed spiders) were recorded.
Of the 99, 68 were by Latrodectus hasselti (redback spiders), 23 by Steatoda spp. (cupboard or button spiders), 5 by Achaearanea spp., and 3 by undifferentiated theridiid spiders.
The seasonal incidence of bites differed, with Steatoda bites occurring throughout the year, and L. hasselti having a large peak over summer.
Presenting the results at a conference of the Australasian College for Emergency Medicine, Dr Isbister said the major symptom of bites was pain, which was severe and persistent, and was similar for all three groups.
This is the first report of bites by Achaearanea spp., and the first series of Steatoda bites that confirms it is similar but less severe than Latrodectus bites (redback spiders).
Dr Isbister advises people to check their shoes before putting them on, and to be careful in dry places, garages, and under outdoor furniture.
He says people should not to panic, as it is very unlikely that a bite will be fatal, so much so that there have been no cases of death for 40 years.
In patients in this study, the pain lasted greater than 24 hours in two-thirds of patients, and was severe enough to prevent sleep in one-third.
The problem, he said, is that people realise how bad the pain is only after it has been going for 24 hours.
At first they think they can put up with it - similarly doctors tend not to worry about the pain alone.
Because the study found that intramuscular antivenom was ineffective and no better than no treatment, it is difficult to give advice on this, he said.
Experience and other research has shown that intravenous antivenom does work - so the problem is the route of administration, not the antivenom itself.
There are currently two trials comparing intravenous and intramuscular antivenom in redback spider bite in Australia (at Dr Isbister's centre in Newcastle, and in Western Australia).
"Hopefully in a couple of years this will mean that we can recommend the appropriate antivenom," he said.
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