A scorpion by any other name is still a scorpion

Pediatric scorpion envenomation in the United States: morbidity, mortality, and therapeutic innovations

In the Southwestern United States, the venom of the scorpion Centruroides sculpturatus (common name bark scorpion) can cause serious and potentially fatal neurotoxicity, with young children most vulnerable to its effects. Historically, advances in the quality of supportive care have made significant improvements in morbidity and mortality. In recent years, the development of effective antivenom therapies has changed the landscape of caring for these patients. This article reviews the background, pathophysiology, diagnosis, and treatment options for C. sculpturatus envenomation. Recent advances in immunotherapy and subsequent implications for pediatric emergency care providers are discussed.

Antivenom for critically ill children with neurotoxicity from scorpion stings

BACKGROUND

Clinically significant scorpion envenomation by Centruroides sculpturatus produces a dramatic neuromotor syndrome and respiratory insufficiency that often necessitate intensive supportive care. We hypothesized that a scorpion-specific F(ab')(2) antivenom would promptly resolve clinical symptoms in children with this syndrome.

METHODS

In a randomized, double-blind study, the efficacy of scorpion-specific F(ab')(2) antivenom, as compared with placebo, was assessed in 15 children 6 months to 18 years of age who were admitted to a pediatric intensive care unit with clinically significant signs of scorpion envenomation. The primary end point was the resolution of the clinical syndrome within 4 hours after administration of the study drug. Secondary end points included the total dose of concomitant midazolam for sedation and quantitative plasma venom levels, before and after treatment.

RESULTS

The clinical syndrome resolved more rapidly among recipients of the antivenom than among recipients of placebo, with a resolution of symptoms in all eight antivenom recipients versus one of seven placebo recipients within 4 hours after treatment (P=0.001). More midazolam was administered in the placebo recipients than in the antivenom recipients (mean cumulative dose, 4.61 vs. 0.07 mg per kilogram of body weight; P=0.01). Plasma venom concentrations were undetectable in all eight antivenom recipients but in only one placebo recipient 1 hour after treatment (P=0.001).

CONCLUSIONS

Among critically ill children with neurotoxic effects of scorpion envenomation, intravenous administration of scorpion-specific F(ab')(2) antivenom resolved the clinical syndrome within 4 hours, reduced the need for concomitant sedation with midazolam, and reduced the levels of circulating unbound venom. (ClinicalTrials.gov number, NCT00685230.)

Serum levels and urine detection of Centruroides sculpturatus venom in significantly envenomated patients

INTRODUCTION

Envenomation by Centruroides sculpturatus can cause systemic signs and symptoms requiring treatment. The toxicokinetics of C. sculpturatus venom has not been described.

METHODS

Venom components were separated for cross-reactivity testing. Serum and urine collected from three patients envenomated by C. sculpturatus had venom levels determined by sandwich enzyme-linked immunosorbent assay (ELISA).

RESULTS

Western blot analysis indicated recognition of C. sculpturatus venom by Alacramyn, an equine F(ab')(2) antivenom developed against Centruroides scorpion venoms, including C. sculpturatus. Serum venom levels in ng/mL with post-envenomation times in minutes (min) were as follows: 85-year-old woman = 8.2 (approximately 150), 2.8 (515), 1.6 (1,200); 14-month-old girl = 29.7 (approximately 50), 5.0 (729); 3-year-old girl = 11.1 (approximately 313), urine venom level of 9.0 (approximately 490).

CONCLUSION

There is sufficient venom cross-antigenicity among different Centruroides species to allow this ELISA technique with Alacramyn to determine serum and urine C. sculpturatus venom concentrations in envenomated patients.

Arachnid envenomation

This article focuses on the medically relevant arachnid species found in North America and selected other arachnids from around the world. While it is largely still true that the geographic location of the envenomation assists in determining the species responsible, the booming trade in arachnids as exotic pets should prompt the clinician to inquire into this possibility. Expert advice should be sought in either case; species identification is critical in determining the need for and proper type of antivenom therapy.

Antivenom treatment in arachnidism

Envenomation by arachnids causes significant medical illness worldwide. Scorpion sting is the most important arachnid envenomation causing adult morbidity and pediatric mortality. Important groups of spiders include the widow spiders (Latrodectus spp.), the recluse spiders (Loxosceles spp.), and two spiders confined to single countries: the Australian funnel web spider (Atrax and Hadronyche spp.) and the armed spider (Phoneutria spp.) from Brazil. There are four widow spider antivenoms available, including the Australian redback spider antivenom and the American black widow antivenom. Despite good in vitro animal work demonstrating effective neutralization with these antivenoms, and cross-reactivity between many species, there continues to be a reluctance to use them in some countries. They are both associated with a relatively low rate of allergic reactions. Redback antivenom is routinely used by the intramuscular route, which may not be as effective as intravenous use based on clinical experience and animal studies. Antivenoms are available for Loxosceles spp., but there is little evidence to support their effectiveness, particularly against local effects. The Australian funnel web spider causes severe neurotoxic envenomation, and antivenom appears to be effective in reported cases. An antivenom exists for the Brazilian armed spider, but is used in only a minority of cases. Many scorpion antivenoms exist worldwide, but there remains significant controversy regarding their efficacy. Animal and human venom level studies demonstrate neutralization of circulating venom in systemic envenomation. Clinical experience in countries where antivenom has been introduced suggests it has reduced pediatric mortality. However, three controlled trials demonstrated that antivenom was not effective, but these included few severe cases. Until controlled trials of antivenom in systemically envenomated patients are undertaken, antivenom use appears justified in severe envenomation. Although envenomation from arthropods is common, no antivenoms exist for these, excepting Lonomia caterpillars in South America, and Ixodes paralysis ticks in Australia.