Approximately 19 of the 115 snake species in the United States are venomous. Snakes inflict about 45,000 bites each year in the United States, of which 8000 are inflicted by venomous snakes. Most bites occur in the warm summer months, when snakes and victims are most active. In the past, it was estimated that mortality from venomous snakebite approached 25 percent. Because of the availability of antivenom and advances in emergency and critical care, mortality rates today are below 0.5 percent. Approximately 5 to 10 deaths occur per year.1
Except for bites by imported species, North American venomous snakebite involves the pit vipers (Crotalidae family) or coral snakes (Elapidae family). The crotalids are represented by the rattlesnakes (Crotalus species), pygmy rattlesnakes and massasauga (Sistrurus species), and the copperheads and water moccasins (Agkistrodon species).
Poisonous snakebites from imported exotic species are infrequent but may occur in zoo personnel as well as in amateur herpetologists. A regional poison center can provide information on snake identification, expected toxicity, and location of antivenom.
The crotalid snakes are called pit vipers because of bilateral depressions or pits located midway between and below the level of the eye and the nostril ( Fig 189-1).
The pit is a heat receptor that guides strikes against warm-blooded prey or predators. Crotalid snakes are also distinguished by two fangs that can be folded against the roof of the mouth, in contrast to the coral snakes, which have shorter, fixed, and erect fangs. Within the pit vipers, the rattle distinguishes the rattlesnake from other crotalids. The mistaken belief that rattlesnakes always rattle before striking has persisted for centuries. In truth, many strikes occur without a warning rattle. 2
FIG. 189-1. Rattlesnake surface anatomy. (Reprinted with permission from Robert E. Hill.)
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