Envenomation

Envenomation is the exposure to a toxic substance secreted by a venomous animal, typically via a bite or sting. Clinical manifestations of envenomation depend on the specific venom and the quantity injected. Signs and symptoms range from mild local pain to neurologic compromise, coagulopathy, and cardiac arrest. Even small quantities of venom (e.g., from a bee sting) may cause life-threatening hypersensitivity reactions in susceptible individuals. Individuals who have been envenomated should always be evaluated for severe systemic reactions and receive therapy specific to the causative venom. Supportive treatment may include cardiac resuscitation, respiratory support, pain management, and/or advanced wound care. Antivenoms are available for use in the treatment of many, but not all envenomations. All antivenoms have a high risk of inducing serum sickness. Individuals who have been envenomated need to be observed for hours to weeks for delayed effects of the venom and/or the treatment. Aspects of animal bites unrelated to envenomation (e.g., infection, mechanical tissue damage) are treated in “Animal bites.”

• Perform a rapid primary survey to identify severe systemic reactions (e.g., anaphylaxis).
• Assess local and systemic symptoms of envenomation.
• Discuss management with the local poison control center; in the US, the Poison Help line is 1-800-222-1222.
• Perform wound irrigation and debridement.
• Manage acute pain.
• Administer antivenom if indicated and monitor for adverse reactions (e.g., anaphylaxis, serum sickness).
• Administer tetanus prophylaxis as indicated.
• Monitor for progression or return of systemic symptoms of envenomation.
• See also “Management of bite wounds.”

Epidemiology ^[1]

• ∼ 5000 venomous snakebites per year in the US. ^[1]
• ∼ 99% of venomous snakebites in the US are from Crotalinae snakes. ^[1]
• ∼ 25% of venomous snakebites are dry (i.e., no venom is released). ^[2]

Overview of snake envenomation

Management of crotaline envenomation differs from coral snake envenomation. ^[3]

Pressure immobilization and/or tourniquets are not recommended as part of routine snake envenomation management in the US. ^[5]

Crotaline envenomation ^[4][6]

Clinical features ^[1][6]

• Local effects: burning pain, ecchymosis, petechiae, blebs, bullae
• Systemic effects: hematotoxicity , neurotoxicity

Local effects are more common than systemic effects with crotaline envenomation. ^[6]

Management

Crotaline antivenom is the mainstay of treatment of moderate to severe crotaline envenomation.

• Follow the general approach to envenomation.
• Obtain CBC, BMP, coagulation panel, CPK, and urinalysis. ^[3][6][7]
• Use clinical and laboratory severity grading to guide specific management.

Crotaline antivenom

• Types
  • Crotalidae polyvalent immune Fab (CroFab)
  • Crotalidae equine immune F(ab′)₂ (ANAVIP)
• Administration: preferably within 4 hours of the snakebite; effective for the first 24 hours ^[8]
• Dosages
  • Low-dose CroFab ^[3][4][6]
  • High-dose CroFab ^[3][4][6]
  • ANAVIP ^[3][4][6]
• Adverse effects: hypersensitivity, serum sickness

Coral snake envenomation ^[6][9]

Clinical features ^[1][6]

• Local effects: mild pain and swelling at the bite site
• Systemic effects: primarily neurotoxicity, e.g., ptosis, paresthesias, dysphagia, muscle weakness, and respiratory failure

Management

• Follow the general approach to envenomation.
• Obtain CBC, BMP, coagulation panel, CPK, and urinalysis. ^[3][6][7]
• Admit to ICU for at least 24 hours.
• Monitor for signs of neurotoxicity.
  • Neuromuscular weakness: cranial nerve examination, muscle strength examination
  • Respiratory depression: continuous capnography, negative inspiratory force measurements
• Administer antivenom if neurotoxicity develops: Micrurus fulvius antivenin

• Perform a rapid primary survey to identify severe systemic reactions.
• Identify the type of snake involved.
• Assess the severity of local and systemic symptoms.
• Discuss management with the local poison control center.
• Administer antivenom, if indicated, e.g.:
  • CroFab OR ANAVIP for grade II–IV crotaline envenomation
  • Coral snake antivenin for coral snake envenomation with neurotoxicity.
• Manage acute pain.
• Perform wound irrigation and debridement.
• Administer tetanus prophylaxis as indicated.
• Monitor for progression or return of systemic symptoms.
• Monitor for adverse reactions of antivenom.
• Observe the patient for a minimum of 8 hours.
• Admit grade II-IV envenomations to the ICU

Overview of spider envenomation ^[6][10][11]

Abdominal pain caused by black widow spider envenomation may mimic the acute abdomen. ^[6][11]

Brown recluse spider envenomation ^[6][10]

Clinical features

• Painless bite develops into erythematous, painful blister within several hours
• Bluish-black skin discoloration usually seen within 24 hours
• Formation of a dark black eschar by the end of the first week (loxoscelism)
• Systemic symptoms (uncommon): nausea, vomiting, fever, hemolysis

Management

• Follow the general approach to envenomation.
• Consider surgical consultation for evaluation of the wound.
• If systemic symptoms occur, obtain:
  • Diagnostics for rhabdomyolysis
  • Diagnostics for DIC
  • Hemolysis workup
• Admit patients with expanding wounds and/or systemic symptoms.

Black widow spider envenomation ^[6][10]

Clinical features

• Painful bite
• Circular red macule that progresses to a target-like lesion
• Systemic symptoms (latrodectism)
  • Muscle pain and rigidity of the extremities, abdomen, and back
  • Autonomic neurologic symptoms (e.g., dyspnea, tachycardia, diaphoresis, nausea)

Management

• Follow the general approach to envenomation.
• Administer benzodiazepines for muscle rigidity.
• Administer black widow spider antivenom (Antivenin (Latrodectus mactans) ) in: ^[6]
  • Patients with severe symptoms
  • Young children
  • Older adults
  • Pregnant individuals
• Observe asymptomatic or mildly symptomatic patients for 6 hours.
• Admit patients with moderate or severe symptoms.

• Perform a rapid primary survey to identify severe systemic reactions.
• Identify the type of spider involved.
• Assess the severity of local and systemic symptoms.
• Discuss management with the local poison control center.
• For severe brown recluse spider envenomation, consider diagnostics for rhabdomyolysis, diagnostics for DIC, and hemolysis workup.
• Administer Latrodectus antivenom for black widow spider envenomation in:
  • Young children
  • Older adults
  • Pregnant individuals
  • Patients with severe symptoms
• Manage acute pain.
• Perform wound irrigation and debridement.
• Administer tetanus prophylaxis as indicated.
• Monitor for progression or return of systemic symptoms.
• Monitor for adverse reactions of antivenom, if administered.
• Consider surgery consult for brown recluse spider bite wounds.
• Observe the patient for a minimum of 6 hours.
• Admit patients with moderate-to-severe toxicity (e.g., systemic symptoms) or expanding wounds.

Hymenoptera order includes bees, wasps, hornets, and fire ants.

Background

• Epidemiology: Hymenoptera stings are responsible for 10% of all anaphylaxis in the US. ^[6]

Clinical features ^[6]

• Local effects
  • Acute pain
  • Swelling, erythema, and itching within minutes
  • Resolve within 2–3 days
  • Large local reactions: swelling and/or redness extending > 10 cm that last for days ^[12]
• Systemic effects: allergic reaction, anaphylaxis

Insects of the Hymenoptera order release venom into tissue by stinging, triggering a local skin reaction and potentially life-threatening systemic reactions.

Management ^[6][13]

• Follow the general approach to envenomation.
• Diagnostic tests are not typically required.

Local reactions

• Remove retained stingers.
• Apply cold compresses.
• Provide acute pain management (e.g., NSAIDs)
• Manage pruritus with oral antihistamines and topical corticosteroids.
• Consider steroid taper for large local reactions.

Anaphylaxis

• Administer epinephrine IM 1:1,000 (1 mg/mL) into the anterolateral thigh.
• See “Management of anaphylaxis” for details.

Massive envenomation ^[13][14]

• Severe systemic reactions and/or delayed organ failure may occur after a swarm attack (typically ≥ 50 stings)
• Perform ABCDE survey.
• Obtain serial labs including CMP and blood pH.

Disposition ^[6]

• Local reaction: discharge with return precautions
• Anaphylaxis: See “Monitoring and disposition” in “Anaphylaxis.”
• Massive envenomation: Admit and monitor for multiple organ dysfunction syndrome.

Provide a prescription and training on epinephrine autoinjector use for patients being discharged after treatment of anaphylaxis from Hymenoptera stings. ^[6]

Bark scorpion ^[6][15][16]

Background

• Distribution: Southwestern US
• Pathophysiology: neurotoxins in the venom inhibit the inactivation of the sodium channels → prolonged depolarization → neuronal membrane hyperexcitability

Clinical features

• Local effects: severe pain, swelling, and erythema at the sting site
• Systemic effects
  • Neuromuscular toxicity
    • Cranial nerve dysfunction (e.g., dysphagia, abnormal eye movements)
    • Somatic skeletal neuromuscular dysfunction (e.g., jerking of extremities, fasciculations)
  • Autonomic dysfunction (e.g., tachycardia, salivation, diaphoresis)
• Duration: Symptoms peak at ∼ 5 hours and may last > 30 hours.

Management

• Follow the general approach to envenomation.
• Diagnostics tests are not routinely recommended. ^[16]
• Antivenom is indicated for cranial nerve and/or neuromuscular dysfunction.
• Use severity grading to guide specific management.

Complications ^[15]

• Rhabdomyolysis
• Aspiration pneumonia
• Respiratory failure
• Pancreatitis (rare)

The following sections cover the venomous aquatic animals most commonly responsible for hospital visits in the US, including animals not native to US waters, which may be popular among aquarists. Wounds caused by aquatic animals are particularly susceptible to infection with Vibrio species, due to contaminated seawater (see “Noncholera Vibrio infection” for more information).

Removing the patient from the water is the most important first step after any marine envenomation. ^[6]

Clinical features and treatment of jellyfish stings vary by species; clinicians should be familiar with the species commonly found in the region in which they practice. ^[18]

• Pathophysiology ^[6]
  • Tentacles containing nematocysts attach to the skin and discharge venom.
  • Venom toxicity varies by species.
• Clinical features ^[6]
  • Local effects
    • Acute pain
    • Linear urticarial lesions
    • Skin necrosis (severe stings)
  • Systemic effects: anaphylaxis, respiratory failure, cardiac arrest
• Diagnostics: not routinely indicated
• Management ^[6][18][19]
  • Follow the general approach to envenomation.
  • Inactivate remaining nematocysts. ^[6][19]
    • Apply vinegar to stings from Hawaiian box jellyfish, Australian box jellyfish, and Portuguese man-of-war.
    • Apply 50% baking soda slurry to lion's mane and Chesapeake Bay sea nettle.
  • Remove the attached tentacles with forceps or a gloved hand.
  • Consider antivenom administration for severe reactions from box jellyfish stings. ^[6]
  • Consider symptomatic relief by applying heat (e.g., heat packs, hot water immersion, warm shower). ^[19]

Avoid applying water to or rubbing the sting sites as this may trigger nematocysts remaining on the skin and cause additional stings. ^[6]

Stingray injuries may result in envenomation, but acute penetrating injuries are more common. Immediate wound management is the priority. ^[20][21]

• Distribution: freshwater and coastal regions
• Epidemiology: 750–2000 stings reported annually in the US ^[20]
• Clinical features: Symptoms of local tissue trauma are more common than systemic effects.
  • Local
    • Laceration or puncture wound, with severe pain that is disproportionate to the injury
    • See also “Penetrating trauma by body region.”
  • Systemic
    • Headache, seizures, syncope
    • Dyspnea
    • Muscle cramps
    • Hyperhidrosis
    • Abdominal pain, nausea, vomiting
    • Cardiac arrhythmias ^[20]
• Diagnostics: x-ray to evaluate for retained foreign body
• Differential diagnosis: stonefish sting
• Management ^[6][20][21]
  • Follow the general approach to envenomation.
  • Begin open wound treatment.
    • Remove the barb, if present.
    • Avoid primary wound closure (due to high infection risk).
    • Consider antibiotics for open wounds in patients with deep puncture wounds or infected marine wounds.
    • See also “Penetrating trauma.”
  • Immerse injury in hot water (42–45°C) for 30–90 minutes (provides analgesia and denatures the venom).
• Complications: infection or necrosis (due to retained barb)

Death or severe injury following a sting ray attack is usually due to penetrating trauma, not envenomation. ^[22]

• Distribution
  • Worldwide, mainly Indian and Pacific Oceans
  • Due to inland aquarium trade, injuries are not limited to coastal areas.
• Clinical features ^[23]
  • Local: intense burning sensation at the puncture site, which radiates proximally
  • Systemic
    • Headache, syncope, weakness
    • Chest pain, dyspnea (due to pulmonary edema)
    • Hyperhidrosis
    • Abdominal pain, nausea, vomiting
  • Potential hypersensitivity reactions, including anaphylaxis
• Diagnostics: x-ray to evaluate for retained foreign body
• Differential diagnosis
  • Sea urchin stings
  • Stingray stings
• Management
  • Follow the approach to envenomation.
  • Immerse injury in hot water (42–45°C) for 30–90 minutes (provides analgesia and denatures the venom).
  • Consider antibiotics for open wounds in patients with deep puncture wounds or infected marine wounds.
  • Consider stonefish antivenom for severe systemic symptoms.
• Complications: wound infection, necrotic ulcers, compartment syndrome, chronic neuropathy

Sea urchin injuries are usually local tissue reactions caused by spines retained in the subcutaneous tissues; significant envenomation is rare.

Clinical features ^[24]

• Local reactions
  • Pain at the puncture site
  • Erythema and edema
  • Blue-black staining of the surrounding skin
• Systemic reactions (rare)
  • Paresthesias and/or paralysis
  • Hypotension
  • Respiratory distress
• Delayed Reactions (from retained spines)
  • Granulomas
  • Synovitis
  • Arthritis

Management ^[24]

• Follow the general approach to envenomation.
• Severe systemic reaction: Prepare to provide respiratory support.
• Remove easily extractable spines.
• Immerse injury in hot water (42–45°C) for 30–90 minutes (provides analgesia and denatures the venom). ^[25]
• Begin open wound treatment.
• Consider antibiotics for open wounds in patients with deep puncture wounds or infected marine wounds.

Do not delay hot water immersion water as toxins and proteinaceous irritants are heat labile. ^[24]