Effects of bites by the European adder (Vipera berus) in seven Swedish horses.

Summary

# European Adder Envenomation in Horses: Clinical Presentation and Outcomes Vipera berus bites in horses present highly variable clinical manifestations depending on venom load, bite location and individual response. This Swedish case series documented seven horses bitten by European adders, with clinical signs ranging from localised swelling to life-threatening systemic complications including systemic inflammatory response syndrome, extensive tissue necrosis, ventricular arrhythmias and dysphagia. Two horses received Zagreb antiserum treatment and survived; of the three untreated cases, all were euthanased due to severe complications, suggesting antiserum may improve survival outcomes, though the small sample size limits definitive conclusions. For equine practitioners in regions where V. berus is endemic, recognition of rapid systemic deterioration—particularly cardiac arrhythmias and airway compromise—is critical for timely intervention and consideration of antivenom therapy. Given the severity of untreated cases in this series, prompt veterinary assessment of horses with suspected adder bites warrants urgent investigation of venom-specific treatments and supportive care protocols to prevent mortality.

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Key Findings

• •Seven horses bitten by European adders presented with clinical signs ranging from mild local swelling to severe systemic manifestations including systemic inflammatory response and cardiac arrhythmias
• •Two horses treated with Zagreb antiserum showed treatment response
• •Three untreated horses required euthanasia due to bite-related complications

Conditions Studied