A Novel Equine F[ab']2 Veterinary Antivenom for North American Viperid Snake Envenomation Demonstrates Efficacy by Rapid Serum Venom Removal and Improvement in Snakebite Severity Score.

OBJECTIVE

To assess the efficacy of a new equine F[ab']2 antivenom (US Department of Agriculture code 6101.05) in removing serum venom and lowering the snakebite severity score (SSS) in animals suffering from naturally occurring viperid envenomation.

DESIGN

Retrospective study, April 2020 to October 2021.

SETTING

Veterinary hospitals across four North American regions.

ANIMALS: Twenty-two dogs, one cat, and one horse.

INTERVENTIONS: All patients received the new antivenom intravenously and were assessed for clinical response. Most dogs required one vial for clinical control of signs.

MEASUREMENTS AND MAIN

RESULTS

Among the dogs and cats with detectable initial serum venom, 94.4% showed a strong response to antivenom administration, with a reduction in serum venom ranging from 94% to >99% at 2 h. Animals that experienced a 90% reduction of serum venom within 2 h greatly exceeded the 0% expected of an ineffective antivenom. The canine and feline SSS improved relative to the initial SSS at 2, 6, and 12 h in 57.9%, 77.8%, and 90.9% of cases, respectively. A favorable reduction in SSS was also appreciated in the single horse in the study.

CONCLUSIONS

In the canine, feline, and equine cases of North American viperid envenomation studied, antivenom 6101.05 adequately removed serum venom and lowered the SSS.