Spider Bite

Introduction

Spider bites are common and rarely require treatment. More significant effects result from Redback spider bite and uncommonly Funnel Web spider envenoming. It is important to have a thorough understanding of these envenomation syndromes.

Red Back Spider envenomation (Latrodectism)

  • Severe and persistent pain, can increase over the bite site over minutes and can last days, but resolves within 1 week
  • Local and regional diaphoresis
  • Piloerection
  • Local erythema
  • Fang marks 5%
  • Systemic features: nausea, vomiting, headache, malaise, abdominal pain, chest pain, HTN, rarely priapism

Funnel Web Spider envenomation

  • Immediate pain
  • Visible puncture marks
  • Local bleeding
  • Autonomic excitation:
    • Diaphoresis
    • Hypersalivation
    • Lacrimation
    • Piloerection
    • HTN
    • Tachy or bradycardia
    • Miosis or Mydriasis
  • Neuromuscular excitation:
    • Paraesthesiae
    • Fasciculations
    • Muscle spasm
  • Non-specific Systemic effects:
    • Nausea & vomiting
    • Headache
    • Abdominal pain
  • Uncommonly: pulmonary oedema, myocardial injury, drowsiness, coma

It has been suggested to consider Australian spider bites into 3 medically relevant groups – Big black spiders, Redback spiders and everything else.1 It is important to consider anyone bitten by a big black spider to have potentially been bitten by a Funnel Web Spider until there are no signs of envenoming after 4 hours.1 If a patient falls in the ‘everything else’ category they can be reassured and discharged without any further treatment required provided their tetanus prophylaxis is up to date.

Management

Redback Spider Bite

  1. The provision of adequate analgesia is the key to managing Redback Spider Bites with envenomation. Recent research has suggested that antivenom is not superior to analgesia2.   It is important to explain that the pain is self-limiting and will resolve although it may take a number of days. Discuss these patients with the toxicology team if achieving adequate analgesia is proving difficult.

Funnel Web Spider Bite

  1. Pressure immobilisation bandage can be applied as first aid measure, it can be taken down at the outset if there are no features of envenomation, or if envenomation is present after antivenom has been commenced.
  2. Assess for features of envenomation; most manifest within 2 hours however it is recommended to observe for at least 4 hours
  3. Antivenom administration is indicated if there are signs of severe envenomation
    • 2 vials of antivenom which can be repeated every 15-30 minutes until envenoming has resolved

Additional Information

  • There have been no reported cases of death attributable to a Redback Spider Bite in over 50 years.
  • Funnel web spiders are distributed from southern Queensland to southern New South Wales, fortunately serious envenoming is rare with 5 to 10 cases each year requiring antivenom1
  • There is no evidence to support that necrotic arachnidism exists in Australia.

Map showing distribution of Funnel Web species in Australia

Further reading

References

  1. Isbister GK. ‘Spider bite: a current approach to management.’ Australian Prescriber 2006; 29(6): 156-8
  2. Isbister GK, Page CB, Buckley NA et al. Randomised controlled trial of intravenous antivenom versus placebo for lactrodectism: The second redback antivenom evaluation (RAVE II) study. Ann Emerg Med 2014; 64(6): 620-628 e2