Efficacy of Australian red-back spider (Latrodectus hasselti) antivenom in the treatment of clinical envenomation by the cupboard spider Steatoda capensis (Theridiidae)

• Steatoda capensis envenomation responded to CSL red-back spider antivenom (RBSAV).
• RBSAV neutralized S. capensis venom at similar doses to red-back spider venom.
• S. capensis venom was more rapidly toxic to insects than Latrodectus venoms.
• Latrodectus venoms were more potent than S. capensis venom in contracting arteries.
• ‘Steatodism’ may overlap more closely with latrodectism than previously recognized.

We describe the first Steatoda capensis envenomation treated with CSL red-back spider antivenom (RBSAV). The patient, a 51-year-old female, developed acute local pain, swelling, redness, and diaphoresis in association with tender lymphadenopathy and hypertension. These features responded, in a dose-dependent manner, to RBSAV. In vitro studies confirmed that RBSAV could neutralize S. capensis venom at equivalent concentrations required to neutralize red-back spider (Latrodectus hasselti) venom. Similar data were obtained using Mexican Latrodectus mactans antivenom (Aracmyn®). Although S. capensis yielded similar quantities of venom protein as L. hasselti, pooled S. capensis and Steatoda grossa venom was more rapidly toxic to insects than either L. hasselti or Latrodectus tredecimguttatus venom. By contrast, both Latrodectus venoms were more potent than S. capensis venom in contracting rat isolated mesenteric arteries. Size-exclusion and anion-exchange chromatography was used to purify a 130 kDa fraction from S. capensis venom that induced contracture and loss of twitch tension in chick isolated biventer cervicis nerve-muscle preparations in a manner similar to α-latrotoxin. This activity was abolished by pre-incubation with RBSAV. We conclude that ‘steatodism’ may overlap more closely with latrodectism than previously recognized and that this bite should be managed in the same way as for Australian red-back envenomation.