Armed spider bite

Background

• Identification: Brown gray with white spots forming a longitudinal band on the dorsal abdomen and a red-brown brush of hair on the chelicerae. Large in size (4.5-6cm) with 4-5mm fangs.
  • They do not form webs, but rather are mobile nocturnal hunters
  • among the largest and most aggressive spiders in South AmericaHabitat restricted to South America, largely Brazil, Argentina, and Uruguay.
• Genus: Phoneutria
• The best-known representative is P. nigriventer, the Brazilian Wandering Spider

Venom

• A complex mixture of polypeptide components. Neurotoxicity is the most clinically relevant.
• Histamine and other components potentiate localized swelling and vascular permeability
• Several neurotoxic components that activate sodium channels, potentiating action potentials and causing uncontrolled muscle contractions.

Clinical Features

• Initial intense pain that radiates to the trunk
• Within 10-20 minutes, onset of systemic toxicity
  • Tachycardia
  • Hypertension
  • Profuse diaphoresis,
  • Salivation
  • Vertigo
  • Vision disturbances
  • Nausea and Vomiting
  • Priapism
• Death has been reported, particularly in children and frail adults, from respiratory paralysis
• Most recover in 24-48hours

Differential Diagnosis

Envenomations, bites and stings

• Hymenoptera stings (bees, wasps, ants)
• Mammalian bites
  • Closed fist infection (Fight bite)
  • Dog bite
• Marine toxins and envenomations
  • Toxins (ciguatera, neurotoxic shellfish poisoning, paralytic shellfish poisoning, scombroid, tetrodotoxin
  • Stingers (stingray injury)
  • Venomous fish (catfish, zebrafish, scorpion fish, stonefish, cone shells, lionfish, sea urchins)
  • Nematocysts (coral reef, fire coral, box jellyfish, sea wasp, portuguese man-of-war, sea anemones)
  • Phylum porifera (sponges)
  • Bites (alligator/crocodile, octopus, shark)
• Scorpion envenomation
• Reptile envenomation
  • Snake bites
    • Crotaline (Pit Vipers)
    • Elapidae (Coral Snakes)
  • Lizard bites
• Spider bites
  • Black widow
  • Brown recluse
  • Tarantula
  • Funnel-web spider bite
  • Armed spider bite

Evaluation

• Generally a clinical diagnosis

Management

• Largely Supportive Care
  • Pain Control
    • Local anesthetic infiltration at site of the bite is effective in 95% of cases
    • Opiates are discouraged as they may potentiate respiratory depression in severe envenomation
• Antivenom
  • Polyvalent and Monovalent formulations available
    • Skin testing and antihistamine ppx recommended prior to use
    • 1-5 vials given IV or IM
  • Clinical response judged by relief of pain or resolution of priapism

Disposition

• May discharge those with no systemic symptoms after period of ED observation
• Admit patients with signs or symptoms of systemic toxicity

See Also

• Envenomations, bites and stings