CLINICAL PRACTICE • Envenomation The funnel web and common spider bites B Nimorakiotakis, MBBS, FACEM, is Staff Specialist, Epworth Hospital and Sunshine Hospital, and Fellow, The Australian Venom Research Unit, Department of Pharmacology, the University of Melbourne, Victoria. KD Winkel, MBBS, BMedSc, PhD, FACTM, is Director, The Australian Venom Research Unit, Department of Pharmacology, the University of Melbourne, Victoria, and President-Elect, the Australasian College of Tropical Medicine. BACKGROUND Spider bites are one of the commonest Sydney funnel web spider The funnel web spiders, encompassed types of bites or stings presenting for man- within the genera Atrax and Hadronyche, agement in general practice and emergency The spider responsible for the most signifi- are the most dangerous spiders in the medicine departments. While in most cases cant bites is the Sydney funnel web spider world. Although the incidence of the responsible species is not identified and (Atrax robustus), a species geographically envenomation is low, funnel web spiders the effects self limited, certain species can limited to an area within 160 km radius of remain a cause of considerable public inflict life threatening bites. the Sydney (New South Wales) central busi- concern. However, most common spider ness district.1 The Sydney funnel web bites produce only minor effects requiring Funnel web spiders spider is a large spider with a glossy black only symptomatic treatment. More than 30 species of the highly danger- cephalothorax and a dark abdomen. The OBJECTIVE ous funnel web spiders are found on the female is larger and more robust than the This article describes the clinical features eastern seaboard of Australia including parts male (Figure 2). The male has a spur on its and treatment of the funnel web spider of South Australia and Tasmania (Figure 1). second leg and the spinnerets (from which and that of its close relative, the mouse The venom appears to be particularly harmful the spider produces silk) of both sexes are spiders. It also covers the question of necrotising arachnidism as well as bites to primates, whereas other mammals are rel- long and obvious, especially the terminal from other common species of spiders. atively unaffected. While many of these spinneret. Both sexes of this species are spiders remain unnamed and the venom very aggressive. When disturbed, they will DISCUSSION unstudied, all funnel web spiders belong rear up ready to strike with their large, Appropriate first aid combined with the either to the genera Atrax or Hadronyche. downward pointing fangs. The female administration of specific antivenom can be Identification and classification of funnel web spider constructs a burrow that may be 30 life saving for funnel web spider bites. True necrotising arachnidism appears to be rare. spiders is often difficult – with some species cm or more deep. Some use crevices in If suspected, clinicians must first consider resembling the less dangerous trapdoor rocks or around house foundations and the very wide differential diagnoses. spiders. Any suspicious spider that has colonies may contain as many as 100 inflicted even an apparently minor injury spiders. The male spiders tend to roam and within the geographic distribution of these often enter houses, particularly during the spiders should be treated as if it were a summer months and in wet weather. Bites funnel web spider. If the spider is captured or may occur when the spider has taken up killed, formal identification is encouraged – temporary residence in bedding, clothing or even a badly damaged spider can often be footwear, or when it is trodden on. successfully identified by arachnologists. Most bites occur in the warmer months, and are predominantly sustained on the 244Reprinted from Australian Family Physician Vol. 33, No. 4, April 2004 Clinical practice: The funnel web and common spider bites Figure 2. Comparison of size and appearance of Figure 3. Female Northern funnel web spider male (left) and female (right) Sydney funnel web Photo courtesy Vern Daffin Figure 1. Geographical distribution of funnel web spiders Photo courtesy Vern Daffin spiders Ç-atracotoxins (Ç-ACTXs). The Ç-ACTXs act • hypertension, tachycardia and vasocon- extremities. Children are especially at risk by slowing sodium current inactivation striction (hypotension may occur later) due to their lower body weight and the resulting in spontaneous repetitive firing of • local and generalised muscle fasciculation potential for multiple bites to occur if spiders action potentials.7 This triggers the release and spasm which may be prolonged and are handled. However, considering the large of excessive – and eventual exhaustion of – violent (facial, tongue or intercostal population at risk, effective envenomation is predominantly sympathetic neurotransmit- muscles, trismus) and difficult to manage. very uncommon. The male species is consid- ters leading to the characteristic biphasic Phase 2 is characterised by: ered to be the most venomous, and all clinical syndrome. • hypotension 13 funnel web spider fatalities documented • hypoventilation and apnoea before the introduction of antivenom in 1980 Symptoms and signs of • continuing acute noncardiogenic pul- have been attributed to the male spider.1 envenomation monary oedema Sydney funnel web spiders are usually easily The initial bite is usually painful and fang • coma, and, finally identifiable to the trained eye, but any large marks are generally seen. The envenomation • irreversible cardiac arrest. dark spider found in the geographic distribu- syndrome is generally characterised by two tion area should be treated with suspicion. phases: the first begins within minutes of the First aid and treatment bite, and the second when the secretions A summary of the recommended first aid and Other funnel web spiders subside – typically many hours later.1 medical treatment for funnel web spider bite There are 12 described species and at least Historically deaths have occurred in either is presented in Figure 4. The key points are: 20 unnamed species in the more widely dis- phase of envenomation. • ensure airway, breathing and circulation tributed genus Hadronyche.2,3 They are also Phase 1 is characterised by: (ABCs) are maintained aggressive spiders with at least six species Local effects: • prompt application of pressure immobilisa- described as having a similar envenomation • bite site may be painful for days to weeks tion bandage (PIB) to the affected limb syndrome to the Sydney funnel web spider.4 because of direct trauma and acidity of venom • transfer to hospital, ideally where As the potency of Hadronyche spp venom but no local necrosis has been recorded antivenom, resuscitation equipment and appears variable in relationship to sex, size, • local swelling, erythema and occasionally monitoring is available health, feeding habits and geographical dis- sweating. • intravenous access should be obtained tribution, all bites from these spiders should General effects: • PIB should be removed only in an area be managed as for the Sydney funnel • numbness around the mouth and spasms/ were appropriate resuscitation can occur web spider. fasciculation of the tongue and antivenom is available. (If PIB has • nausea and vomiting, abdominal pain, been removed and the patient deterio- Pathogenesis acute gastric dilatation rates it should be re-applied) Although most funnel web spider bites are • profuse sweating, salivation, lacrimation, • local tissue enzymes may inactivate the thought to be ineffective or ‘dry’, the clini- piloerection venom, therefore the use of PIB may not cal syndrome can be devastating and has • severe dyspnoea as a result of noncardio- only be helpful in delaying the onset of been lethal in both adults and children. genic pulmonary oedema symptoms, but may allow for a degree of While the causative venom is multicompo- • mental status can rapidly progress from inactivation of the venom nent, the key neurotoxins are the confusion to irrationality or coma • administer antivenom as per protocol in Reprinted from Australian Family Physician Vol. 33, No. 4, April 2004245 Clinical practice: The funnel web and common spider bites Figure 4 if systemic signs of envenoma- caution in the event of hypotension antivenom in 1980, there have been no deaths tion are present because of noncardiogenic pulmonary reported and time required in hospital has dra- • until antivenom is available supportive care oedema matically decreased from an average of 14 days8 of the envenomed patient may include: – relapse is possible and may manifest to less than 2 days.1 Moreover, the antivenom is – supplemental oxygen as dyspnoea secondary to noncardio- extremely safe – no cases of anaphylaxis have – atropine (0.6 mg initial dose for an adult) genic oedema which usually responds been reported and only one case of serum sick- to reduce salivation and bronchorrhoea to further antivenom (this should not ness has been associated with the antivenom.9 – nasogastric aspiration because of be confused with iatrogenic pulmonary gastric dilatation oedema as a result of intravenous Mouse spiders – muscle relaxants and sedatives to facil- overload, particularly in children) Mouse spiders (Missulena spp) are medium itate mechanical ventilation and control • if no symptoms or signs of envenomation sized and robust spiders found throughout intracranial pressure have started 4 hours after the removal of first mainland Australia. Currently there are – intubation and ventilation for respiratory