Snakebites

Snakebites are a rare cause of morbidity and mortality, as the majority of snakes are nonvenomous. Crotalidae and Elapidae are 2 families of venomous snakes. These snakes’ venom results in increased capillary permeability, hemolysis, tissue necrosis, and allergic reactions. Evidence of envenomation at the bite site includes edema, erythema, warmth, bullae, and necrosis. Systemic symptoms such as nausea, diaphoresis, paresthesias, and altered sensorium may be present. In addition, coral snake venom can cause flaccid muscles. The diagnosis is clinical. Management includes supportive care, pain control, hydration, and antivenom. Patients are monitored closely for shock, coagulopathy, respiratory failure, and renal failure.

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Overview

Epidemiology

  • Approximately 15% of snake species worldwide are dangerous.
  • Worldwide: > 100,000 deaths yearly
  • In the United States:
    • Approximately 45,000 snakebites per year
    • 7,000–8,000 of these bites are venomous.
    • < 10 deaths per year 
    • Rattlesnakes cause the most fatalities.

Clinically relevant species

Some important venomous snakes in the United States include:

  • Crotalidae family (accounts for 95% of cases in the United States):
    • Rattlesnakes
    • Copperheads
    • Cottonmouths (also known as water moccasins)
  • Elapidae family: coral snakes

Western diamondback rattlesnake:
A highly excitable, aggressive rattlesnake responsible for a significant portion of the venomous snake bites and most of the snakebite fatalities reported in the United States each year

Image: “8133” by U.S. Department of Health & Human Services. License: Public Domain

Pathophysiology

  • Not all snake bites result in envenomation.  
  • Snake venom often contains:
    • Proteins
    • Proteases
    • Collagenase
    • Phospholipases
    • Other enzymes
  • Envenomation effects:
    • Local and systemic allergic response
    • ↑ Capillary permeability → extravasation of plasma
    • Hemolysis and coagulopathy
    • Tissue necrosis
    • Acetylcholine receptor antagonism at neuromuscular junctions (coral snake)

Clinical Presentation

General presentation

  • Bite marks may not be visible.
  • Clinical signs depend on:
    • Age and size of the victim
    • Species of snake
    • Number and location of bites
    • Quantity and toxicity of the venom
  • Bite-site findings:
    • Fang marks 
    • Scratches

Local signs of envenomation

  • Edema and erythema of bite site and surrounding tissue
  • Oozing from the wound
  • Tender regional lymphadenopathy
  • Warmth over the bite area
  • Ecchymosis
  • Bullae development
  • Necrosis

Index finger of a patient’s right hand displaying an area of focal necrosis following a bite from a snake in the Crotalidae family

Image: “21010” by U.S. Department of Health & Human Services. License: Public Domain

Systemic signs of envenomation

  • Nausea and vomiting
  • Diarrhea
  • Diaphoresis
  • Anxiety
  • Paresthesias
  • Altered sensorium
  • Cranial nerve palsies
  • Flaccid muscles (including respiratory muscle paralysis)

Complications

  • Hypotension and shock
  • Thrombocytopenia
  • Coagulopathy and spontaneous bleeding
  • Compartment syndrome
  • Airway swelling
  • Respiratory failure
  • Renal failure

Diagnosis and Management

Diagnosis

The diagnosis of a snake bite is clinical and aided by the identification of the snake.

Management

  • General measures:
    • Immobilize the affected extremity.
    • Wound cleansing and care
    • Ensure that tetanus immunizations are up to date.
    • Hospital monitoring for signs of envenomation
    • A poison control center should be consulted.
    • Monitor laboratory studies:
      • Coagulation panel
      • Hemoglobin and platelets
      • Renal function
  • Medical therapy:
    • Intravenous fluid hydration
    • Opioids for analgesia (NSAIDs may worsen coagulopathy)
    • Vasopressors for shock
    • Antivenom
  • The use of tourniquets, icing the wound, and “cutting and sucking” are not helpful and should be discouraged.

Differential Diagnosis

  • Dog and cat bites: can cause superficial and deep tissue destruction as well as serious wound infections. The wound type depends on the animal but can include tearing, crush, or puncture wounds. Damage to deeper tissues, such as vessels, tendons, and bone, may occur. The diagnosis is clinical, and cultures should be obtained if the wound appears infected. Management requires fastidious wound care and antibiotics for high-risk or infected wounds. 
  • Spider bites: the brown recluse spider contains a necrotizing venom that can lead to a painful, blistering, necrotic wound; fevers; myalgias; hemolysis; seizures; and renal failure. A black widow spider’s neurotoxic venom can cause muscle cramping and rigidity, vital sign instability, lacrimation, salivation, ptosis, and respiratory distress. The diagnosis is clinical. Management includes wound care, pain management, antivenom for black widow bites, and delayed debridement of necrotic tissue in brown recluse bites.
  • Insect sting: bee, wasp, and ant stings can cause envenomation with localized swelling. Some patients will develop a severe allergic reaction, including anaphylaxis. Neurologic manifestations, coagulopathy, and tissue necrosis are not usually present. The diagnosis is clinical. Management includes removing the stinger (if present), antihistamines, pain control, and emergency care for anaphylaxis.
  • Scorpion sting: most scorpion stings are harmless. However, the bark scorpion is venomous. Patients will have pain and swelling at the site of the sting. Systemic manifestations can include muscle spasms, diaphoresis, abnormal neck and head movements, tachycardia, hypertension, and respiratory distress. The diagnosis is clinical. Management includes supportive care, pain control, benzodiazepines for muscle spasms, and antivenom.
  • Deep venous thrombosis: blood clotting in the deep veins of an extremity. This clotting may be asymptomatic or present with limb swelling, erythema, and pain. A bite site and systemic symptoms are not present. The diagnosis is confirmed with vascular ultrasound. Unless there are contraindications, this condition is managed with anticoagulation.

References

  1. Kasturiratne A, Wickremasinghe AR, de Silva N, Gunawardena NK, Pathmeswaran A, Premaratna R, et al. (2008). The global burden of snakebite: a literature analysis and modeling based on regional estimates of envenoming and deaths. Medline. https://reference.medscape.com/medline/abstract/18986210
  2. Wills BK, Billet M, Rose SR, Cumpston KL, Counselman F, Shaw KJ, et al. (2020). Prevalence of hematologic toxicity from copperhead envenomation: an observational study. Clin Toxicol (Phila). Medline. https://reference.medscape.com/medline/abstract/31342795
  3. Ahmed SM, Ahmed M, Nadeem A, Mahajan J, et al. (2008). Emergency treatment of a snake bite: Pearls from literature. J Emerg Trauma Shock.
  4. Mowry JB, Spyker DA, Brooks DE, Zimmerman A, Schauben JL. (2015). Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS): 33rd Annual Report. Medline. https://reference.medscape.com/medline/abstract/28004588
  5. Barish RA, Arnold T. (2020). Snakebites. [online] MSD Manual Professional Version. Retrieved March 24, 2021, from https://www.msdmanuals.com/professional/injuries-poisoning/bites-and-stings/snakebites
  6. Meyers, SE, Tadi P. (2021). Snake toxicity. [online] StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK557565/
  7. Greene S, Bush SP. (2020). Snakebite. In Alcock, J. (Ed.), Medscape. Retrieved March 24, 2021, from https://emedicine.medscape.com/article/168828-overview

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