ACMT Toxicology Visual Pearl – Along Comes a Spider

4. Sydney Funnel Web Spider (Atrax robustus)

Background [1-3]

The Sydney funnel web spider is geographically distributed in eastern Australia near populated areas, and most activity occurs within the summer months when males are searching for mates. When disturbed, the Sydney funnel web spider can inject deadly venom which has been associated with fourteen reported fatalities. They burrow in moist, cool, sheltered habitats and build a funnel-shaped web.

What are the symptoms of a Sydney funnel web spider bite? [3-5]

• Nausea and vomiting
• Salivation
• Diaphoresis
• Facial paresthesia
• Muscle fasciculations and cramping
• Autonomic instability: Tachycardia or bradycardia, hypertension or hypotension
• Pulmonary edema
• Cerebral Edema
• Deaths can occur within 15 minutes, particularly in small children.

What is the toxin in Sydney funnel web spider venom? [3-7]

• Venom from male spiders contains d-Atracotoxin-Ar1 (also known as robustoxin) which slows and inactivates voltage-gated sodium channels.
• The venom is thought to have developed during evolution for defense against larger predators.
• After envenomation, symptoms typically occur within minutes, and rarely beyond two hours.
• Fortunately, only 10-15% of bites are estimated to be venomous.

How do you treat a Sydney funnel-web spider bite? [3,4,8-10]

• Cleanse the bite site with soap and water.
• Field immobilization and a pressure wrap are recommended within 4 hours post-bite to delay symptom onset until the patient arrives at a medical facility.
• Patients should be monitored for 4-6 hours post envenomation for the development of systemic effects, and at least 2 hours after removal of immobilization bandages.
• Funnel Web Spider Antivenom (FWSAV), introduced in 1981, has been associated with symptom resolution and decreased mortality.
• FWSAV is indicated for signs of systemic toxicity.
  • Initial dose: 2 vials intravenously
  • Repeat dosing: 2 vials intravenously after 15 minutes if required.
  • Most patients only require 2 vials
  • Patients rarely require more than 4 vials in total.
• In Australia, the universal number for the Poisons Information Centre is 13 11 26.

Bedside Pearls

• In an endemic area, funnel web spider envenomation can be deadly.
• Immobilization and a pressure bandage are recommended in the field.
• Monitor for at least 4-6 hours post envenomation.
• Administer Funnel Web Spider Antivenom in patients with systemic toxicity.
• In Australia, contact the Poisons Information Centre at 13 11 26 for management advice.