Residency · Residency · Emergency Medicine

Envenomations: Snakebite and Marine Toxins

Introduction

Envenomation injuries present unique challenges to the emergency physician, requiring knowledge of venom pathophysiology, antivenom indications, and species-specific management. In the United States, pit vipers (rattlesnakes, copperheads, cottonmouths) account for the vast majority of venomous snakebites, while coral snake bites are rare but potentially lethal. Marine envenomations, while less common, include stingray injuries, jellyfish stings, and encounters with venomous fish. Timely recognition and appropriate treatment can be limb- and life-saving.

Pit Viper Envenomation

Epidemiology and Identification

Approximately 7,000 to 8,000 venomous snakebites occur annually in the United States, resulting in fewer than 10 deaths per year. The Crotalidae family includes rattlesnakes (which cause the most severe envenomations), copperheads (the most common), and cottonmouths (water moccasins). Identification features include a triangular head, vertical elliptical pupils, a heat-sensing pit between the eye and nostril, and a single row of subcaudal scales, though identification should not delay treatment. Importantly, 20 to 25 percent of bites are "dry bites" in which no venom is injected.

Venom Pathophysiology

Pit viper venom is a complex mixture of metalloproteinases (causing tissue destruction), phospholipase A2 (causing hemolysis and myotoxicity), serine proteases (causing coagulopathy), and other enzymes. Local effects include pain, progressive edema, ecchymosis, hemorrhagic bullae, and tissue necrosis. Systemic effects include coagulopathy (thrombocytopenia, hypofibrinogenemia, elevated INR), hypotension, neurotoxicity (seen with some rattlesnake species, particularly the Mojave rattlesnake), and rhabdomyolysis.

Clinical Assessment and Grading

Minimal envenomation presents with local pain and swelling confined to the bite site, no systemic symptoms, and normal laboratory values. Moderate envenomation shows progressive swelling beyond the bite site, mild systemic symptoms such as nausea and perioral paresthesias, and mild lab abnormalities. Severe envenomation is characterized by rapidly progressive swelling involving the entire extremity, significant systemic symptoms including hypotension and altered mental status, marked coagulopathy, and concern for compartment syndrome.

Management

Initial management follows the ABCs: the airway should be secured if the bite is to the face or neck with progressive edema, large-bore IV access should be established, and cardiac monitoring initiated. Constrictive jewelry and clothing should be removed from the affected extremity, which should be immobilized at or below heart level. Harmful interventions must be avoided -- no tourniquets, ice, incision and suction, or electric shock. The leading edge of swelling should be marked with a pen and timed at 15- to 30-minute intervals to track progression. Serial laboratories every 4 to 6 hours should include CBC, fibrinogen, PT/INR, CK, and BMP.

Antivenom

Crotalidae Polyvalent Immune Fab (CroFab) is the first-line antivenom, derived from sheep and indicated for progressive local swelling, coagulopathy, or systemic symptoms. The initial dose is 4 to 6 vials IV over 60 minutes after reconstitution, with reassessment in 1 hour. If initial control is not achieved, an additional 4 to 6 vials should be administered. Maintenance dosing consists of 2 vials every 6 hours for 3 additional doses to prevent recurrent coagulopathy and swelling. Crotalidae Immune F(ab')2 (Anavip) is an alternative antivenom with a longer half-life, given as a 10-vial initial dose that may require fewer maintenance doses. Copperhead bites are often managed without antivenom if local effects are mild, as antivenom reduces pain and swelling but may not change functional outcomes. Poison Control (1-800-222-1222) should be contacted for all envenomations.

<image>Progression of pit viper envenomation showing three stages: initial bite with fang marks and minimal swelling, moderate envenomation with edema extending beyond the bite site with ecchymosis, and severe envenomation with massive extremity swelling, hemorrhagic bullae, and tissue discoloration, with serial markings showing the advancing edge of edema</image>

Coral Snake Envenomation

Coral snakes belong to the Elapidae family and are found in the southeastern United States (Eastern coral snake) and Arizona (Sonoran coral snake). The identification mnemonic "red on yellow, kill a fellow; red on black, venom lack" applies to North American species only. Coral snake venom is primarily neurotoxic, acting through postsynaptic acetylcholine receptor blockade, with minimal local tissue effects. The onset of symptoms is delayed by hours and progresses through ptosis, diplopia, dysarthria, dysphagia, progressive descending paralysis, and respiratory failure. North American Coral Snake Antivenom (equine-derived) should be administered empirically for confirmed coral snake bites regardless of symptoms due to the delayed onset, though supply is extremely limited. If antivenom is unavailable, management is supportive with airway management and mechanical ventilation as needed, and effects may persist for days to weeks.

Marine Envenomations

Jellyfish Stings

The box jellyfish (Chironex fleckeri), found in the Indo-Pacific, is the most dangerous jellyfish and can cause rapid cardiovascular collapse. Box jellyfish antivenom is available in Australia. The Portuguese man-of-war has trailing tentacles that cause immediate severe pain and linear erythematous wheals. Treatment involves removing tentacles with forceps (never bare hands) and rinsing with vinegar (5 percent acetic acid) for box jellyfish and most tropical species to inactivate nematocysts. Fresh water should never be used as it causes nematocyst discharge. Hot water immersion provides pain relief. Irukandji syndrome is a delayed systemic reaction (20 to 30 minutes) from small carybdeid jellyfish, producing a catecholamine surge with severe hypertension, tachycardia, and pulmonary edema, treated with IV magnesium and nitrates.

Stingray Injuries

The barbed tail of a stingray causes a traumatic laceration with envenomation, most commonly affecting the feet and ankles when someone steps on a ray in shallow water. The venom is heat-labile, so immersing the wound in hot water (45 degrees Celsius / 113 degrees Fahrenheit) for 30 to 90 minutes provides pain relief. Wound care includes copious irrigation, debridement of devitalized tissue, and removal of retained barb fragments (with plain films if a retained fragment is suspected). Primary closure is generally avoided due to high infection risk. Prophylactic antibiotics with a fluoroquinolone or TMP-SMX should cover Vibrio species, and tetanus prophylaxis should be administered.

Venomous Fish (Scorpionfish, Lionfish, Stonefish)

Dorsal fin spines inject venom causing intense pain, edema, and occasionally systemic symptoms such as hypotension, cardiac arrhythmias, and seizures (particularly with stonefish). The venom is heat-labile, making hot water immersion at 45 degrees Celsius the first-line treatment. Stonefish antivenom is available for severe envenomations (an Australian product). Wound care and antibiotic prophylaxis are similar to stingray injuries.

<image>Illustration comparing three common marine envenomations: jellyfish sting showing tentacle contact pattern with linear nematocyst wheals on the skin surface, stingray barb laceration on the dorsum of the foot, and lionfish dorsal spine puncture wound on the hand, each with an inset showing the venom delivery mechanism</image>

Sea Urchin Injuries

Sea urchin spines cause pain and local inflammation upon puncture, and spines may break off and embed in tissue. Treatment involves hot water immersion for pain and removal of accessible spines. Retained deep spines may be left to resorb or may require surgical removal if located in a joint. Granulomatous reactions occur rarely.

Clinical Pearls

Progressive swelling, coagulopathy, or systemic symptoms after a pit viper bite warrant antivenom administration, and treatment should not be delayed for identification of the snake species. Coral snake envenomation has a deceptively delayed presentation, and antivenom should be administered empirically for confirmed bites. Hot water immersion at 45 degrees Celsius is the first-line treatment for pain from stingray, lionfish, and scorpionfish envenomations due to heat-labile venom proteins. Poison Control should be contacted for all envenomations for species-specific guidance and antivenom sourcing. Harmful first-aid measures for snakebite must be avoided: no tourniquets, incision and suction, ice, or electric shock.

References

1. Lavonas EJ, Ruha AM, Banner W, et al. Unified treatment algorithm for the management of crotaline snakebite in the United States: results of an evidence-informed consensus workshop. BMC Emerg Med. 2011;11:2.
2. Gold BS, Dart RC, Barish RA. Bites of venomous snakes. N Engl J Med. 2002;347(5):347-356.
3. Lakkis NA, Maalouf GJ, Mahmassani DM. Jellyfish stings: a practical approach. Wilderness Environ Med. 2015;26(3):422-429.
4. Clark RF, Girardo S, Rao D, et al. Stingray envenomation: a retrospective review of clinical presentation and treatment in 119 cases. J Emerg Med. 2007;33(1):33-37.

Read this lecture as Markdown