Disorders Caused by Venomous Snakebites and Marine Animal Exposures¶
Chapter 471 | Part 14: Poisoning, Drug Overdose, and Envenomation
KEY CLINICAL POINTS¶
- Venomous snakebites and marine envenomations are leading causes of preventable morbidity and mortality in tropical and subtropical regions.
- Antivenom is the cornerstone of treatment for severe envenomation, with specific formulations for different venom types (e.g., Crotalidae polyvalent immune Fab for pit vipers).
- Pressure-immobilization bandages are critical for delaying systemic venom absorption, but must be removed promptly to avoid compartment syndrome.
- Marine envenomations from cnidarians (jellyfish, corals) require immediate decontamination with seawater and vinegar, with hot water immersion for pain relief.
- Ciguatera and paralytic shellfish poisoning are foodborne neurotoxicoses caused by marine toxins, requiring supportive care and avoidance of contaminated seafood.
1. DEFINITION & OVERVIEW¶
Venomous snakebites and marine animal exposures are medical emergencies caused by toxins injected via bites or stings. Envenomation can lead to local tissue damage, systemic toxicity, and multiorgan failure. Management requires rapid identification of the causative agent, supportive care, and specific antivenom therapy.
Table 471-1: Management of Venomous Snakebites in the US and Canada¶
| Action | Details |
|---|---|
| Stabilize Airway/Breathing/Circulation | Immediate intervention for respiratory compromise |
| Monitor Vital Signs | Continuous cardiac rhythm, oxygen saturation, and blood pressure monitoring |
| Administer Antivenom | Crotalidae polyvalent immune Fab (CroFab®) or Anavip® based on snake type |
| Pressure-Immobilization Technique | Wrap bitten limb with snug bandage, elevate to heart level |
| Antivenom Dosing | Moderate envenomation: 4–6 vials CroFab®; Severe: 6 vials CroFab® |
1.1 Snakebite Pathophysiology¶
Venom composition varies by species: pit vipers (coagulopathy, myotoxicity), elapids (neurotoxins), and colubrids (less potent). Local effects include necrosis, hemorrhage, and systemic effects like coagulopathy, renal failure, and neurotoxicity.
1.2 Marine Envenomation Mechanisms¶
Cnidarians (jellyfish, corals) release venom via nematocysts, causing pain, inflammation, and systemic toxicity. Marine toxins like ciguatoxin and saxitoxin are heat-stable and accumulate in seafood, leading to neurotoxic and paralytic syndromes.
2. EPIDEMIOLOGY¶
Global snakebite mortality is estimated at 81,400–138,000 annual deaths, with 50% projected increase by 2030. Most cases occur in developing countries with tropical climates. Marine envenomations are less common but contribute to significant morbidity in coastal regions.
Table 471-2: Acetylcholinesterase Inhibitors for Neurotoxic Envenomation¶
| Action | Dosage |
|---|---|
| Test Dose of Edrophonium | 10 mg IV (children: 0.25 mg/kg) |
| Neostigmine Rescue | 0.02 mg/kg IV/IM (children: 0.04 mg/kg) |
| Atropine Pretreatment | 0.6 mg IV (children: 0.02 mg/kg) |
2.1 Regional Burden¶
Asia and Africa account for 80% of snakebite deaths. Coral snake bites (Micrurus spp.) are more common in the Americas, while sea snake envenomation is prevalent in coastal regions of Australia and Southeast Asia.
2.2 Marine Envenomation Trends¶
Cnidarian stings account for 15–20% of marine-related emergencies. Box jellyfish (Chironex fleckeri) and sea urchins are leading causes of severe marine envenomation in tropical regions.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Venom composition varies by species: pit vipers (coagulopathy, myotoxicity), elapids (neurotoxins), and colubrids (less potent). Marine toxins include neurotoxins (ciguatoxin), neurotoxins (saxitoxin), and hemolysins (sea urchin venom).
3.1 Snake Venom Components¶
Pit viper venoms contain metalloproteases, phospholipases, and hemolysins. Elapid venoms include neurotoxins that block neuromuscular junctions. Colubrid venoms are less toxic but may cause local irritation.
3.2 Marine Toxin Mechanisms¶
Ciguatoxin (domoic acid) activates glutamate receptors, causing neuroexcitation. Saxitoxin blocks sodium channels, leading to paralysis. Sea urchin venom contains bradykinin-like peptides and hemolysins.
4. CLINICAL FEATURES¶
Local symptoms include pain, swelling, and necrosis. Systemic effects vary by venom type: coagulopathy (pit vipers), neurotoxicity (elapids), and hemolysis (marine toxins). Severe cases may present with respiratory failure, renal failure, or cardiovascular collapse.
4.1 Snakebite Presentation¶
Pit viper bites: Local necrosis, hemorrhage, and coagulopathy. Elapid bites: Neurotoxicity (dysphagia, respiratory failure). Colubrid bites: Local irritation with minimal systemic effects.
4.2 Marine Envenomation Symptoms¶
Cnidarian stings: Immediate pain, erythema, and urticaria. Sea urchin injuries: Local necrosis, hemorrhage, and systemic hemolysis. Box jellyfish envenomation: Severe pain, skin necrosis, and cardiovascular instability.
5. DIFFERENTIAL DIAGNOSIS¶
Snakebites must be differentiated from insect bites, allergic reactions, and other infections. Marine envenomations should be distinguished from dermatitis, bacterial infections, and other cutaneous conditions.
5.1 Snakebite Mimics¶
Insect bites (localized pain), allergic reactions (urticaria), and bacterial infections (purulent wounds).
5.2 Marine Envenomation Mimics¶
Contact dermatitis (itching, rash), bacterial infections (erythema, warmth), and sunburn (pain, erythema).
6. INVESTIGATIONS & DIAGNOSIS¶
Laboratory tests include coagulation studies (PT, aPTT), creatinine, and electrolytes. Imaging (ultrasound, MRI) may identify retained foreign bodies. Antivenom-specific assays and toxin detection are critical for confirmation.
Table 471-3: Ciguatera Poisoning Symptoms¶
| System | Symptoms |
|---|---|
| Gastrointestinal | Nausea, vomiting, diarrhea, abdominal cramps |
| Neurologic | Paresthesias, vertigo, ataxia, dysgeusia |
| Cardiovascular | Bradycardia, hypotension, arrhythmias |
| Dermatologic | Urticaria, skin vesiculations, dermographism |
6.1 Diagnostic Tests¶
CBC, coagulation profile, creatinine, and urinalysis. 20-min whole-blood clotting test for coagulopathy in resource-limited settings.
7. MANAGEMENT & TREATMENT¶
Immediate first aid includes immobilization, wound cleaning, and antivenom administration. Supportive care includes fluid resuscitation, airway management, and monitoring for complications like compartment syndrome.
Table 471-1: Antivenom Dosing Guidelines¶
| Envenomation Severity | Antivenom Dose |
|---|---|
| None/Mild | No antivenom |
| Moderate | 4–6 vials CroFab® or 10 v01s Anavip® |
| Severe | 6 vials CroFab® or 10 vials Anavip® |
7.1 Antivenom Therapy¶
Crotalidae polyvalent immune Fab (CroFab®) for pit vipers; Antivenin (Micrurus fulvius) for coral snakes. Dosing based on envenomation severity and regional protocols.
7.2 Compartment Syndrome¶
Early recognition with pressure monitoring. Fasciotomy reserved for refractory cases. Pressure-immobilization bandages should be removed promptly to avoid ischemia.
8. PROGNOSIS & COMPLICATIONS¶
Mortality rates vary by region and venom type: <1% in the US with antivenom. Complications include renal failure, respiratory failure, and secondary infections. Long-term sequelae include chronic neuropathy and functional disability.
8.1 Snakebite Outcomes¶
Morbidity is high in developing countries due to limited access to antivenom. Severe envenomation may result in permanent disability or death.
8.2 Marine Envenomation Risks¶
Ciguatera and paralytic shellfish poisoning can cause prolonged neurologic symptoms. Severe cases may require prolonged hospitalization and supportive care.
9. SPECIAL CONSIDERATIONS¶
Pregnancy, pediatric, and geriatric patients require tailored management. Antivenom use in pregnancy is generally safe, while marine toxins may cross the placenta. Pediatric patients are at higher risk for systemic toxicity from small venom volumes.
9.1 Pregnancy¶
Antivenom is safe in pregnancy; avoid unnecessary procedures. Monitor for fetal distress and maternal coagulopathy.
9.2 Pediatrics¶
Children are at higher risk for systemic envenomation. Dosing adjustments for antivenom and analgesics are required.
10. KEY POINTS & CLINICAL PEARLS¶
- Antivenom is the mainstay of treatment for severe envenomation. 2. Pressure-immobilization bandages delay systemic absorption but must be removed promptly. 3. Marine toxins like ciguatoxin and saxitoxin are heat-stable and require supportive care. 4. Early recognition of neurotoxicity and prompt antivenom administration improve outcomes. 5. Compartment syndrome is a critical complication requiring surgical intervention.