Etiology

Snakebites are generally sustained during outdoor activities, although amateur snake collectors may sustain them while handling snakes and herpetologists or zoo personnel may sustain them at work. Generally, snakes do not regard humans as prey and only bite as a defensive action. Rattlesnakes frequently, although not always, warn of their presence (with their rattle) before striking. Around 67% of snakebites occur during intentional snake exposures such as snake handling, snake hunts, and aggravating snakes in the wild, and 40% of casualties consumed alcohol prior to sustaining the bite.[14]

Although occupational exposure to snakebite is rare in North America, it is more common in parts of the developing world. People who work outdoors, such as agricultural workers, woodcutters, forestry workers, and snake charmers, may be exposed to snakebites in the occupational setting.[15]

Pathophysiology

All snakebites carry the risks associated with puncture wounds, including local soft-tissue infection and tetanus. Snake fangs or teeth may break off during the bite and be retained as a foreign body, increasing the risk for infection. A significant percentage of bites by venomous snakes are "dry" and do not involve envenomation. Envenomations also vary in the volume of venom injected into the victim.

  • Crotalinae (pit viper) venoms are considered to be hematotoxic. They contain a variety of enzymes and bioactive small molecules that cause local inflammation and necrosis, increased blood vessel permeability, and activation of the coagulation cascade.​[1]​

  • Elapidae (coral snake) venoms are considered to be neurotoxic. They exhibit weak proteolytic, phosphodiesterase, and nucleotidase activities, and exhibit moderate-to-strong phospholipase A activity, and a variable amount of acetylcholinesterase activity.[16] Elapidae venom has a direct, irreversible toxic effect on striated myocytes, with swelling of individual fibers and hyaline degeneration resulting in decreased cardiac and skeletal muscle contractility.[17] The venom also causes a nondepolarizing competitive blockade of neuromuscular transmission at acetylcholine sites.[2]

Classification

Venomous snake characteristics (US)

Crotalinae (pit viper):

  • Venoms are considered to be primarily hematotoxic. The Mojave rattlesnake (Crotalus scutulatus) is a crotaline with predominantly neurologic sequelae.

  • Includes rattlesnakes, sidewinders, copperheads, cottonmouths, and water moccasins.

  • All have a pit organ located between the nostril and the eye, and a triangular head.

  • Rattlesnakes have a distinctive rattle at the end of their tail that they shake when threatened.

Elapidae (coral snakes):

  • Venoms are considered to be neurotoxic.

  • There are only 3 species of coral snake (family Elapidae) in the US, each with limited geographic distribution:

    • The Eastern coral snake (Micrurus fulvius fulvius) is found east of the Mississippi river in the states of Louisiana, Mississippi, Alabama, Georgia, Florida, and South Carolina, and in the southeastern tip of North Carolina.

    • The Texas coral snake (Micrurus tener) is found west of the Mississippi river in Louisiana, Texas, the southwestern tip of Arkansas, and Mexico.[2]

    • The Sonoran coral snake (Micruroides euryxanthus) is found in Arizona and New Mexico, but is rarely responsible for human envenomation.[3]

  • A mnemonic that helps differentiate venomous coral snakes from nonvenomous snakes on the basis of their skin color is: "Red next to yellow will kill a fellow. Red next to black, venom lack."

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