Venomous Creatures: Black Widow Envenomation (Latrodectism)

Spider bites are a common occurrence in the United States. While most bites are benign, there are two types of spiders with clinical importance to emergency physicians because their venom can cause significant systemic manifestations. These are widow spiders and brown spiders. Missed diagnosis is common for both bite types, and delayed treatment can lead to significant morbidity. This article reviews the distinguishing characteristics of widow spider bites, the clinical syndrome caused by black widow venom, emergency department management, indications for and dosing of antivenom, and disposition.

BACKGROUND

Widow spiders are so-called because the female eats the male after mating. In the United States, the most common widow spider is the black widow, characterized by the classic red hourglass seen on the ventral abdomen. However, color and shape variations exist.  

From: Swanson DL et al. Clinical Manifestations and diagnosis of widow spider bites. UpToDate.

From: http://watchingtheworldwakeup.blogspot.com/2008/06/black-widows-part-1-chemistry-of-venom.html

CLINICAL MANIFESTATIONS AND TREATMENT

The initial bite of a widow spider can be painless or only cause minor pain. However, within 30 – 120 minutes, generalized symptoms can manifest. Black widow venom contains alpha-latrotoxin which binds presynaptic nerve terminals and stimulates the release of neurotransmitters such as acetylcholine, norepinephrine, dopamine, glutamate, and enkephalin.  

The resulting clinical syndrome known as latrodectism can range from mild symptoms of localized pain to severe symptoms of sympathetic and parasympathetic hyperactivity, including tachycardia, hypertension, nausea, and vomiting. A common board-review presentation is a spider bite that presents as an acute or surgical abdomen. One rare but distinguishing feature is that of localized or asymmetric diaphoresis, especially below the knees. Treatment is mostly supportive, but in severe cases, antivenom is indicated.

Labs: not helpful

Antivenoms:

• Antivenom (whole horse IgG)
  • Initial Dose: 1 vial (reconstituted in 2.5mL sterile diluent + 250mL NS) over 1hr
    • May repeat x 2 q1hr (if symptoms persist)
  • Shortens duration of symptoms to <24hrs
  • Side Effects: allergic reactions, serum sickness
  • Pregnancy category C (but still give if pregnant)
  • Pediatrics: same dose

**Consult with poison control center before administration**

• Analatro aka F(ab)2 antivenom
  • Initial Dose: 3 vials (reconstituted in 50mL NS) over 10min
  • Reduces pain more quickly
  • Only available in clinical trials

DISPOSITION

• Discharge: Mild or moderate/severe envenomations successfully controlled with antivenom
• Admit: Ongoing requirement of parenteral analgesia

Resources:

• Basanou E et al. Treatment of black widow spider (Lactrodectus mactans) envenomation: A review of 53 cases. Clin Toxicol. 2015;53:281.
• Clark RF.  The safety and efficacy of antivenin Lactrodectus mactans.  J Toxicol Clin Toxicol.  2001;39:125.
• Dart RC, Bigdan G, Heard K, et al.  A randomized, double-blind, placebo-controlled trial of a highly purified equine F(ab)2 antibody black widow spider antivenom. Ann Emerg Med. 2013;61:458.
• Isbister GK, Graudins A, White J, Warrel D.  Antivenom Treatment in Arachnidism. J Toxicol Clin Toxicol.  2003; 41:291-300.
• Monte AA, Bucher-Bartelson B, Heard KJ.  A US Perspective of Symptomatic Lactrodectus spp Envenomation and Treatment: A national poison data system review.  Ann Pharmacother.  2011;45:1491-1498.
• Monte AA.  Black widow spider (Lactrodectus mactans) antivenom in clinical practice. Cur Pharm Biotechnol.  2012;13:1935-1939.
• Ryan NM, Buckley NA, Graudins A.  Treatments for Latrodectism – A systematic Review on Their Clinical Effectiveness.  Toxins 2017;9:148.
• Saucier JR. Arachnid Envenomation. Emerg Med Clin N Am.  2004;22:405-422.
• Swanson DL et al.  Clinical Manifestations and diagnosis of widow spider bites.  UpToDate.
• Vetter RS, Swanson DL, Weinstein SA, White J.  Do spiders vector bacteria during bites? The evidence indicates otherwise.  Toxicon.  2015;93:171.
• Vetter RS, Swanson DL, Weinstein SA, White J.  Management of widow spider bites. UpToDate.
• Yan S, Wang X.  Recent Advances in Research on Widow Spider Venoms and Toxins.  Toxins 2015:7:5055-5067.

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