What are the signs and symptoms of a venomous snake bite?

Signs and Symptoms of Venomous Snake Bite

Venomous snake bites in North America present with distinct clinical patterns depending on the snake family: pit viper bites (95% of cases) cause immediate local tissue injury with pain, swelling, and redness at the bite site, while coral snake bites produce neurotoxic effects with minimal local findings but progressive paralysis developing within minutes to hours. 1

Pit Viper Envenomation (Rattlesnakes, Copperheads, Cottonmouths)

Local Signs (Most Common Presentation)

• Fang marks at the bite site, though these may not always be visible 2
• Pain at the bite site that begins immediately and spreads gradually from the wound 3
• Progressive swelling and edema of the affected extremity that develops within 30 minutes and continues to spread 1, 3
• Redness, warmth, and tenderness at and around the bite site 1
• Ecchymoses (bruising) that develops as venom spreads through tissues 4, 2

Systemic Signs (Moderate to Severe Envenomation)

• Hematologic abnormalities including progressive decrease in platelet count, potentially dropping below 100,000/mm³ due to platelet aggregation activity of the venom 3
• Coagulopathy with abnormal bleeding and clotting parameters 2
• Hypotension and shock in severe cases 1, 2
• Muscle fasciculations that may progress to paralysis 1
• Systemic symptoms including vomiting, weakness, and altered mental status 3

Timing Considerations for Pit Vipers

• Patients who develop pain, swelling, ecchymoses, systemic symptoms, or abnormal laboratory findings within 30 minutes to one hour of a bite are probable candidates for antivenom therapy 4
• The majority of copperhead bites (85%) result in grade 1 envenomations with minimal systemic effects 5

Coral Snake Envenomation (Elapidae Family)

Neurotoxic Presentation

• Minimal to no local tissue injury at the bite site, which distinguishes coral snake bites from pit viper bites 6
• Progressive paralysis developing within minutes to hours after the bite 1
• Neuromuscular weakness that can rapidly progress to respiratory compromise 6
• Potential loss of consciousness in severe cases 3

Critical Distinction

• The absence of significant local swelling or pain does NOT rule out serious envenomation with coral snakes, as their neurotoxic venom primarily affects the nervous system rather than causing tissue destruction 6, 7

Severe Envenomation Warning Signs

Immediate Red Flags Requiring Urgent Antivenom

• Rapid platelet count drop to <10,000/mm³ within 1 hour, suggesting direct intravascular injection of venom 3
• Hypofibrinogenemia with elevated fibrinogen degradation products, indicating disseminated intravascular coagulation 3
• Cyanosis, hypotension, or loss of consciousness 3
• Any signs of respiratory compromise or difficulty breathing, particularly with suspected coral snake bites 6

Common Pitfalls in Assessment

• Do not assume a "dry bite" (no envenomation) based solely on absence of immediate symptoms, as some manifestations may be delayed; observation for at least 8-12 hours is warranted 2
• Do not rely on snake identification by the patient, as misidentification is common; treat based on clinical presentation and geographic likelihood 3
• Recognize that copperhead bites rarely cause severe systemic toxicity, but all venomous snake bites warrant medical evaluation to assess for the minority of cases requiring intervention 5
• Remember that coral snake bites may appear benign initially but can rapidly progress to life-threatening neurotoxicity requiring ventilatory support 6

Timeline of Symptom Development

• Pit viper local effects: Pain and swelling typically begin within minutes and progress over hours 3
• Pit viper systemic effects: Coagulopathy and systemic symptoms develop over 1-6 hours if they occur 4, 2
• Coral snake neurotoxicity: Can begin within minutes but may be delayed up to several hours, requiring prolonged observation 1, 6