Spider bites

T63.3

The vast majority of spiders are not harmful to humans.

SPIDER BITES, NEUROTOXIC (WIDOW/BUTTON SPIDERS)

DESCRIPTION

The term latrodectism is used to describe the systemic symptoms and signs following envenomation by the bite of the Latrodectus spider species (widow spiders). Most cases are caused by the bite of a black widow spider; brown widow spider bites are usually milder and characterized by local swelling.

DIAGNOSTIC CRITERIA

  • Bites are felt immediately as a pinprick sensation, followed by increasing local pain that may spread to include the entire extremity.
  • Typical target lesions, i.e. erythematous ring surrounding a pale center.
  • Spasms in large muscle groups, abdominal pain or rigidity, progressing to generalised pain involving the trunk and abdomen have been described.
  • Paraesthesia of hands and feet.
  • Sweating and anxiety may occur.

GENERAL AND SUPPORTIVE MEASURES

  • Supportive care of airway, breathing and circulation.

MEDICINE TREATMENT

For pain and muscle cramps:

  • Calcium gluconate 10%, IV, 0.5 mL/kg by slow intravenous injection.
    • Give 0.5–1 mL/minute.
    • Monitor ECG and respiration.

For severe envenomation (if systemic symptoms are present):

  • Spider antivenom, IV infusion, 5–10 mL diluted in sodium chloride 0.9% or dextrose 5%, 50–100 mL administered over 5–10 minutes.

SPIDER BITES, NECROTIC ARACHNIDISM

T63.3

DESCRIPTION

Violin/recluse (Loxosceles) spiders can produce local necrotic skin lesions that are mediated by enzymes.

DIAGNOSTIC CRITERIA

  • Bites are initially painless.
  • Skin lesions can vary from mildly erythematous lesions to severe local reaction, i.e. blistering, bluish discolouration progressing to frank necrosis.
  • Systemic effects include nausea, vomiting, fever, chills, arthralgia, haemolysis, thrombocytopaenia, haemoglobinuria and renal failure.

GENERAL AND SUPPORTIVE MEASURES

  • Supportive care.
  • Surgical debridement may be required once the clear margins around the necrotic lesions are established.

MEDICINE TREATMENT

For pain:

  • Paracetamol, oral, 15 mg/kg/dose, 6 hourly as required.

If severe pain:

  • Morphine, IV, 0.1 mg/kg/dose 4 hourly.
    • Monitor for respiratory depression.

Antibiotic therapy for septic lesions.