Systemic toxicity from a widow bite is the result of alpha-latrotoxin, a potent neurotoxin, which causes the presynaptic release of the major neurotransmitters – acetylcholine, norepinephrine, dopamine, and glutamate – throughout the entire nervous system. Repeated discharge results in depletion of these neurotransmitters from the synaptic vesicles at the nerve endings. Clinical signs and symptoms are shown in Table 1. Symptoms usually resolve in 24 to 48 hours.

Pain is the primary reason patients present for treatment following a widow spider bite. Treatment includes proper wound care, ensuring updated tetanus status, and focusing on symptomatic relief using parenteral opioids and benzodiazepines. Barbiturates, dantrolene, antihistamines, and intravenous calcium have all been used with minimal success.⁴ Latrodectus antivenin is the only treatment that can shorten the duration of symptoms, but it is not universally available. The antivenin is derived from horse serum, similar to the older Crotalidae polyvalent antivenin.

CRITICAL DECISION

Which patients with findings consistent with a black widow spider bite should be given antivenin?

Patients with severe refractory pain not relieved by parenteral opioids or benzodiazepines are candidates for antivenin.^4,5 One vial of antivenin diluted in 100 to 250 mL of saline should be infused over 2 hours.⁶ The major adverse effects from antivenin administration are anaphylaxis and delayed allergic reactions.

Recluse

There are six species of Loxosceles indigenous to the United States —Loxosceles arizonica, Loxosceles deserta, Loxosceles devia, Loxosceles blanda, Loxosceles apachia, and Loxosceles reclusa. The brown recluse (L. reclusa) is the most common recluse spider in North America. As the name implies, recluse spiders are not aggressive, preferring dark, dry locations. They are mostly nocturnal. Both sexes are venomous.⁷ Unlike widow spiders, recluse spiders are found only in distinct geographic locations, generally from Kansas to Kentucky and from southern Iowa to Louisiana. Considerable controversy arises over reported recluse bites in patients with dermonecrotic lesions that occur outside of locations where recluse spiders are known to live.^7,8 The differential diagnosis (Table 2) is broad for loxoscelism.