Necrotising arachnidism

In 1976, Southcott brought Loxosceles to the attention of Journal readers, reporting its occurrence in Adelaide and Sydney.³ From the late 1970s an increasing number of patients have been presenting to doctors throughout Australia with bites resulting in local tissue injury, ranging from a tiny ulcer through to very extensive areas of full-thickness skin necrosis.^2,4 Following a report of one such case in the Journal,⁵ Sutherland, in an editorial entitled "Watch out, Miss Muffet!", speculated on causative organisms, mentioning, in particular, the white-tailed spider (currently designated Lampona cylindrata).⁶

Since then Australian poisons information centres have seen a steady increase in calls about definite or suspected spider bite, and such calls are now the single most common reason for calling a poisons information centre,⁷ with a 30% increase in calls related to spider bite in the last two years alone. Casual conversation with many urban general practitioners will often reveal that they see a small but growing number of cases of suspected spider bite resulting in local tissue injury, varying from mild to quite severe. Currently, there is no system for national collection of these case data to ascertain the true extent of the problem, nor to confirm that numbers of cases are rising. In many cases the bite is ascribed to the white-tailed spider, despite a singular lack of evidence.

The white-tailed spider is a common native urban spider, frequently found in homes, where it roams in search of prey.² Published venom research and case reports of bites have been reviewed and do not reveal evidence that this spider commonly causes tissue injury.^8,9 There are only four published case reports of tissue injury and in none of these cases was the spider formally identified.^10-12Pincus et al add a further 12 cases, but in only three cases was the spider formally identified by an expert. In two this was a white-tailed spider, while the third case involved a black house spider (Badumna species). This adds to the still scarce case reports of necrotic bites by identified spiders and, most importantly, provides three cases with expert identification.

Of the two confirmed white-tailed spider bite cases reported, one developed shallow ulcers only, the other a small ulcer that healed within one month. Both cases are therefore at the mild end of the necrotising arachnidism spectrum.

What is the mechanism of injury in necrotising arachnidism and how might we treat it? Recluse spiders have been studied in detail, but the mechanism of venom injury is still contentious.² Worse, in North America, where these spiders are native and frequently cause bites, there is neither concordance on treatment nor a clearly effective treatment.² Experience there does suggest that early surgical debridement may extend the lesion, that early skin grafting usually fails, that antibiotics are unhelpful unless there is a clearly identified and targeted secondary infection and that no specific therapy is helpful, with the possible exception of hyperbaric oxygen therapy.² This treatment for necrotising arachnidism is being tried in a number of hyperbaric units around Australia, with mixed but encouraging success.¹¹ It is probably time to formalise this by running a multicentre trial to establish the validity and indications for this form of treatment.

In the only two cases I have seen in South Australia where a spider was clearly caught biting and subsequently identified, it was a recluse spider (Loxosceles), not a white-tailed spider.² In my experience with many cases of necrotising arachnidism over nearly 20 years, the white-tailed spider is often suspected but never confirmed to be the culprit. In most cases, a spider is found in the house after the bite and an unsubstantiated link is made.

The increasing tendency of the media and the medical profession to blame the white-tailed spider for necrotising arachnidism is unfortunate, as it establishes a common belief that the cause is known when in truth it is not. In Brazil, wolf spiders were long blamed for necrotising arachnidism until a detailed study showed that recluse spiders were the culprits.¹³ A concerted effort to determine which species of spiders (or perhaps some other organism) can cause necrotising arachnidism should become a prime focus for research in this field. Once a cause is known, specific treatments can be more reliably investigated and preventive measures devised.

Julian White
Clinical Toxinologist
Women's and Children's Hospital, Adelaide, SA

1. Pincus GL, Winkel KD, Hawdon GM, Sutherland SK. Acute and recurrent skin ulceration after spider bite. Med J Aust 1999; 171: 99-102.
2. White J, Cardoso JL, Fan HW. Clinical toxicology of spider bites. In: Meier J, White J, editors. Handbook of clinical toxicology of animal venoms and poisons. Boca Raton: CRC Press, 1995: 259-329.
3. Southcott RV. Spiders of the genus Loxosceles in Australia. Med J Aust 1976; 1: 406-408.
4. Sutherland SK. Spider bites in Australia; there are still some mysteries [editorial]. Med J Aust 1983; 2: 597.
5. Spring W. A probable case of necrotizing arachnidism. Med J Aust 1987; 147: 605-607.
6. Sutherland SK. Watch out, Miss Muffet! [editorial]. Med J Aust 1987; 147: 531.
7. New South Wales Poisons Information Centre. 1998 Annual Report. Sydney: New Children's Hospital, 1999.
8. White J, Hirst D, Hender E. 36 cases of bites by spiders, including the white-tailed spider, Lampona cylindrata. Med J Aust 1989; 150: 401-403.
9. Atkinson RK, Wright LG. Studies of the necrotic actions of the venoms of several Australian spiders. Comp Biochem Physiol 1991; 98: 441-444.
10. Grey M. A significant illness that was produced by the white-tailed spider, Lampona cylindrata [letter]. Med J Aust 1989; 151: 114-116.
11. Skinner MW, Butler CS. Necrotising arachnidism treated with hyperbaric oxygen. Med J Aust 1995; 162: 372-373.
12. Chan SW. Recurrent necrotising arachnidism. Med J Aust 1998; 169: 642-643.
13. Ribeiro LA, Jorge MT, Piesco RV, Nishioka S deA. Wolf spider bites in Sao Paulo, Brazil; a clinical and epidemiological study of 515 cases. Toxicon 1990; 28: 715-717.