Among the 14 families of snakes, five are poisonous (Table II–56). The annual incidence of snakebite in the United States is three to four bites per 100,000 population. Clinically significant morbidity occurs in fewer than 60% of cases, and only a few deaths are reported each year. Bites from rattlesnakes are the most common snake envenomation in the United States, and the victim is often a young intoxicated male who was teasing or trying to capture the snake. Snakes strike accurately to about one-third of their body length, with a maximum striking distance of a few feet.
Table II-56 Poisonous Snakes (Selected) |Favorite Table|Download (.pdf)
Table II-56 Poisonous Snakes (Selected)
Families and Genera
Human envenomation difficult because of small mouth and small, fixed fangs in the rear of mouth. Larger African species may cause severe systemic coagulopathy.
Human envenomation difficult because of small mouth and small, fixed fangs in rear of mouth. Neurotoxicity usually predominates.
Also have small, rear-located fangs.
Viperidae, subfamily Crotalinae
Most common envenomation in United States. Long, rotating fangs in front of mouth. Heat-sensing facial pits (hence the name “pit vipers”).
Viperidae, subfamily Viperinae
Puff adder, gaboon viper
Long, rotating fangs in front of mouth, but no heat‐sensing facial pits.
Mechanism of toxicity. Snake venoms are complex mixtures of 50 or more components that function to immobilize, kill, and pre-digest prey. In human victims, these substances produce local “digestive” or cytotoxic effects on tissues as well as hemotoxic, neurotoxic, and other systemic effects. The relative predominance of cytotoxic, hemotoxic, and neurotoxic venom components depends on the species of the snake and on geographic and seasonal variables. This changing mix of components is the most likely reason why the clinical presentation of each rattlesnake envenomation is unique.
Toxic dose. The potency of the venom and the amount of venom injected vary considerably. About 20% of all snake strikes are “dry” bites in which no venom is injected.
Clinical presentation. The most common snake envenomations in the United States are from rattlesnakes (Viperidae, subfamily Crotalinae). Bites from common North American Elapidae (eg, coral snakes) and Colubridae (eg, king snakes) are also discussed here. For information about bites from other exotic snakes, contact a regional poison control center (1-800-222-1222) for a specific consultation.
Crotalinae. Fang marks may look like puncture wounds or lacerations, with the latter resulting from a glancing blow by the snake or a sudden movement by the victim. The fangs often penetrate only a few millimeters but occasionally enter deeper tissue spaces or blood vessels. Signs and symptoms of toxicity are almost always apparent within 8–12 hours of envenomation.
Local effects. Within minutes of envenomation, stinging, burning pain ...