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Snake Envenomation, Coral
Updated: Dec 17, 2008
Introduction
Background
Approximately 40-50 species of venomous coral snakes exist in North America and South America, with the greatest variety from Mexico to northern South America. A number of African and Asian coral snake species also exist. All coral snakes belong to the family Elapidae; Micrurus fulvius (eastern coral snake) and Micrurus tener (Texas coral snake) are the most important species in the United States.
Another US coral snake is Micruroides euryxanthus (Sonoran or Arizona coral snake); this is a relatively innocuous snake, and no deaths have been attributed to its bite.
Coral snakes tend to be relatively shy creatures, and bites are uncommon. Coral snakes account for fewer than 1% of venomous snakebites in the United States. Most people bitten by coral snakes are handling them intentionally. Most bites occur in the spring or fall.
Pathophysiology
The coral snake venom apparatus is composed of a pair of small, fixed, hollow fangs in the anterior aspect of the upper jaw through which the snake conducts venom via a chewing motion (see Media file 2). Unlike pit vipers, such as rattlesnakes, copperheads, and cottonmouths, which strike quickly, coral snakes must hang on for a brief period to achieve significant envenomation in humans.
Coral snake skull.
Coral snake venoms tend to have significant neurotoxicity, inducing neuromuscular dysfunction. They have little enzymatic activity or necrotic potential compared with most vipers and pit vipers. These venoms tend to be some of the most potent found in snakes, yet the venom yield per animal is less than that of most vipers or pit vipers. Because of the relatively primitive venom delivery apparatus, as many as 60% of those bitten by North American coral snakes are not envenomed.
Frequency
United States
Probably fewer than 20 bites per year (though 99 alleged bites were reported to the American Association of Poison Control Centers in 2004).1
International
No accurate information on international incidence is available.
Mortality/Morbidity
No deaths related to coral snake bites have been reported in the United States since coral snake antivenom became available. Before that time, the estimated case-fatality rate was 10%, and the cause of death was respiratory or cardiovascular failure. Patients who survive the bite may require respiratory support for up to a week and may suffer persistent weakness for weeks to months.
Clinical
History
The vast majority of patients bitten by coral snakes report that a brightly colored snake bit them.
North of Mexico City, including the United States, the color pattern of the snake can be helpful in differentiating a coral snake from a harmless mimic (eg, nonvenomous milk snake). In this region, all coral snakes have a red, yellow, black, yellow, red banding pattern (red and yellow touching, see Media file 1); most harmless mimics have a red, black, yellow, black, red pattern (red and yellow separated by black). The mnemonic "Red on yellow, kill a fellow; red on black, venom lack," may be helpful in this region. South of Mexico City, the banding patterns are much less helpful, and bicolor (red and black) species are also present.
Snake envenomations, coral. Comparison of the harmless Lampropeltis triangulum annulata (Mexican milksnake) (top) with Micrurus tener (Texas coral snake) (bottom). Photo by Charles Alfaro.
History may include the following:
- Onset of symptoms may be delayed up to 10-12 hours but may then be rapidly progressive.
- Paucity of local complaints
- Local paresthesias (may be painful)
- Soft tissue swelling (usually mild)
- Alteration of mental status
- Complaints related to cranial nerve dysfunction (eg, diplopia, ptosis, difficulty swallowing)
Physical
Physical findings of snake bite may include the following:
- Impending respiratory failure
- Respiratory distress
- Pharyngeal spasm
- Hypersalivation
- Cyanosis
- Trismus
- Neurologic dysfunction
- Altered mental status
- Ptosis
- Generalized weakness
- Muscle fasciculations
- Cardiovascular collapse
- Hypotension
- Tachycardia
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References
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Davidson TM, Eisner J. United States coral snakes. Wilderness Environ Med. 1996;1:38-45.
German BT, Hack JB, Brewer K, et al. Pressure-immobilization bandages delay toxicity in a porcine model of eastern coral snake (Micrurus fulvius fulvius) envenomation. Ann Emerg Med. Jun 2005;45(6):603-8. [Medline].
Gray S. Pressure immobilization of snakebite. Wilderness Environ Med. Spring 2003;14(1):70-1. [Medline].
Kitchens CS, Van Mierop LH. Envenomation by the Eastern coral snake (Micrurus fulvius fulvius). A study of 39 victims. JAMA. Sep 25 1987;258(12):1615-8. [Medline].
Norris RL, Bush SP. North American venomous reptile bites. In: Auerbach PS, ed. Wilderness Medicine. 4th ed. St. Louis: Mosby; 2001:896-926.
Norris RL, Dart RC. Apparent coral snake envenomation in a patient without visible fang marks. Am J Emerg Med. Jul 1989;7(4):402-5. [Medline].
Norris RL, Ngo J, Nolan K, et al. Physicians and lay people are unable to apply pressure immobilization properly in a simulated snakebite scenario. Wilderness Environ Med. 2005;16(1):16-21. [Medline].
Parrish HM, Khan MS. Bites by coral snakes: report of 11 representative cases. Am J Med Sci. May 1967;253(5):561-8. [Medline].
Simpson ID, Tanwar PD, Andrade C, et al. The Ebbinghaus retention curve: training does not increase the ability to apply pressure immobilisation in simulated snake bite--implications for snake bite first aid in the developing world. Trans R Soc Trop Med Hyg. May 2008;102(5):451-9. [Medline].
Further Reading
Keywords
snake envenomation, snakebite, snake bite, coral snake, Elapidae, Micrurus fulvius, eastern coral snake, Micrurus tener, Texas coral snake, coral snake envenomations, coral snake bite, Micruroides euryxanthus, Sonoran coral snake, Arizona coral snake
