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<< Diagnosis And Management Of North American Snake And Scorpion Envenomations

Epidemiology And Etiology

Given the multitude of people who have an intense and occasionally irrational fear of snakes, it is hard to believe that snakebites are a relatively infrequent occurrence. Even harder to believe, is that fatalities from snake envenomations are exceedingly rare. It is estimated that there are approximately 45,000 snakebites per year in the United States.12 Seven thousand to 8000 of these bites are attributed to venomous snakes, but these bites only result in five to six deaths annually.3,12 The Toxi Exposure Surveillance System (TESS) report for 2004 breaks down snakebites by species, with 98% of bites by venomous snakes in the US from the Crotalids; there were a total of 5046 reported bites, with 167 major complications and two deaths. TESS reported 97 coral snake envenomations in 2004, with four major complications and no deaths. Envenomations by poisonous exotic snakes resulted in 131 reported cases in 2004. These bites were more severe than coral snakebites with morbidity and mortality rates similar to that of rattlesnakes; about 35% moderate injury, 7% major injury, and one death.

One of the major limitations of the data reported by TESS is that, generally speaking, the data is compiled only from snake envenomations that result in visits to a physician (ED or other) or a call to the regional or national Poison Control Center. Many people who sustain minor envenomations or dry bites (bites where no venom is injected) will not seek medical care. It is reasonable to conclude that the patients who do not seek medical care generally will not take the time to report their envenomation to TESS. Thus, authors of scientific and medical writings are left to speculate on the true incidence of envenomations. The current consensus seems to be based on the estimate given by Parish in a 1954 report on the incidence of treated snakebites in the US (45,000),12 and a report by Langley and Morrow estimating that the actual incidence and death rate from snakebites was three to four times that reported by TESS.3 The majority of deaths occur among children and the elderly, among those for whom antivenom is not given, is postponed, or is administered in insufficient quantities, and among members of fundamentalist religious groups who handle poisonous snakes during religious rituals.13

Rattlesnakes, with their presence in virtually all of the continental US and the high potency of their venom, are responsible for the majority of snakebite fatalities with the diamondback rattlesnake accounting for 95% of these fatal bites.14-15

Snakebites are more common during the spring and summer months when both snakes and people are more active outdoors. Very little has changed in the literature regarding the demographics of snake envenomations since 1966, when Parish published one of the first comprehensive survey results in Public Health Reports.12 Best summarized by Gold et al, "the majority of victims remain men between the ages of 17 and 27 years. More than 95% of the bites are on the extremities, and most occur between April and October, the peak months being in July and August."4 Nonetheless, an emergency physician in any part of the country can potentially see snakebites at any time of the year, often from deliberate exposure to captive snakes.16

Of the nearly 3000 species of venomous and nonvenomous snakes worldwide, there are less than 40 species of venomous snakes in North America. To simplify things even further for the non-herpetologist, the venomous species of North America can be divided into four main types: Rattlesnakes (consisting of species from both the Crotalus and the Sistrurus genus), copperheads (genus Agkistrodon), cottonmouths (genus Agkistrodon), and coral snakes. The first three types are members of the Viper family and the Crotalinae subfamily; coral snakes are North America's only native member of the family of snakes called Elapids.4,17 The family Elapidae also includes many of the most dangerous snakes in the world including cobras, kraits, adders, and mambas. Three different species of Elapids can be found in North America from North Carolina to Arizona and as far south as several hundred miles south of the US-Mexican border. The Eastern coral snake (Micrurus fulvius) is the most dangerous of the coral snakes. The highest concentrations are found in Florida, but it has also been found from North Carolina to Louisiana. The Western coral snake (Micruroides euryxanthus) is found in the Sonoran Desert of Arizona, northern Mexico, and the southwest corner of New Mexico below 5800 feet. The third Elapid in the US is the Yellow-bellied sea snake (Pelamis platurus). It has weak venom relative to the other Elapids, but it can still be dangerous to humans. The range of this sea snake in North America is limited to the southernmost areas of California and the northern pacific coast of Mexico. Exotic snakes are held by collectors and zoos in scattered places throughout the country and may represent any of the venomous species found in the world, but are most commonly cobras, kraits, and true vipers (as opposed to the pit vipers).

Scorpions

Scorpions are arthropods in the class Arachnida, sharing some characteristics with spiders, and are found worldwide. Most species of scorpions deliver venom that is not dangerous to humans, but there are a noteworthy few that deliver a potent, although not deadly, venom. In the US, scorpions are found primarily in the desert Southwest, with only one species, the Bark scorpion Centruroides sculpturatus (aka exilicauda), dangerous to humans. The Bark scorpion is only found in Arizona and Northern Mexico.

The South African and Tunisian scorpions are very different from the Southwestern scorpion. In the US, most envenomations are treated at home, with very few advancing to pulmonary edema or shock. Most of the large case series and controlled trials have been performed outside the US, and caution must be used when extrapolating these studies to the management of patients in the US.

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Last Modified: 08/17/2017
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