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red back spider bites / Latrodectism


  • the red back spider ((L hasselti)) belongs to the widow spider family (Latrodectus sp.) and are a common cause of spider bite in Australia with 3,000-5,000 bites per annum which result in Latrodectism which is primarily due to neurotoxins such as alpha latrotoxin
  • most bites occur when people accidentally put their hand in the web and the spider feels threatened, or put on clothing containing a spider

clinical features of Latrodectism

  • the most consistent and prominent symptom is pain at the bite site which generally increases over the 1st hour and may spread proximally up the limb
  • this may be associated with other local features such as sweating, local erythema, piloerection, and systemic features such as:
    • nausea, malaise
    • headache
    • abdominal pain
    • tachycardia
    • hypertension
    • diaphoresis elsewhere (eg. bilateral legs)
  • in some cases, there may also be:
    • paraesthesiae
    • fever
    • muscle spasms and even some patchy paralysis
  • it is rarely lethal (none since 1950 in Australia) although bites to babies may be a significant risk
  • effects generally last 1-4 days and nearly all resolve within 1 week

Mx in ED

  • unlike snake bites:
    • first aid principles of compression and immobilisation are NOT indicated and may increase the pain
    • there is generally NO need for blood tests nor IV cannulation, unless you also suspect snake bite
    • there are NO diagnostic tests - the diagnosis is clinical
    • antivenom may NOT be needed even in those with envenomation
    • consider using an ice pack locally
  • it is rare for victims to require any Rx other than analgesia (although these analgesic regimes tend to be poorly effective in these bites) such as:
  • historically most victims were given im or iv red back antivenom, however, a recent study by Isbister et al suggests that the benefits of antivenom in reducing pain, systemic symptoms or sequelae in those over 8 years of age may not outweigh the 3-4% risk of allergic reaction 1)
  • older children and adults generally do not need observation in hospital, nor anti-venom
  • it may be prudent to given anti-venom to younger children and consider admission for observation, particularly in the very young
redback_spider.txt · Last modified: 2020/02/22 10:20 (external edit)