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Over 3000 species of snakes have been identified worldwide, with nearly 800 species considered venomous. All venomous species are classified taxonomically into one of four general groups. These include the families Viperidae, Elapidae, and Colubridae, as well as the Atractaspidinae, a subfamily of the Lamprophiidae family.49 The United States is home to nearly 30 species and subspecies of venomous snakes (Table 122–1), with many more found throughout Mexico. All belong to the Crotalinae subfamily of Viperidae or to the Elapidae family.

TABLE 122–1.Medically Important Snakes of the United States

Venomous snakes possess glands that are associated with specialized teeth, or fangs, which allow delivery of venom for the purpose of prey immobilization or defense. Fangs are located in the front of the mouth in most venomous species. In addition to fangs, venomous snakes have rows of small teeth that may cause additional injury during a bite.

The majority of snake species in North America are rear-fanged, non-venomous members of the Colubridae family. Bites by these species, which include corn snakes, gopher snakes, and garter snakes, are usually harmless. Colubrids do not possess venom glands, but may produce secretions from Duvernoy’s glands that contain toxins similar to those found in the venom of venomous species. Although the vast majority of bites by nonvenomous colubrids do not produce symptoms, rare cases of envenomation have been documented following a bite by a nonvenomous species.57

Venomous snakes are found throughout most of the United States. They are much more common in the southern and western states than in the northern states. Though venomous species are not endemic to Maine, Alaska, or Hawaii, bites have been reported in every state except for Hawaii. The true number of bites that occur each year is not accurately known, but an average of 5000 native venomous snakebites are reported to US poison centers annually.43 Mortality is rare, with fewer than 10 deaths per year reported. Epidemiologic data on snakebites in Mexico is poor, but the number of bites and deaths is thought to be higher.29

The majority of snakebites occur between April and September, ...

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