The only poisonous snakes in the United States are pit vipers (Crotalidae) and coral snakes (Elapidae). Pit vipers include rattlesnakes, water moccasins (cottonmouths), and copperheads. They have a pitted depression between their eyes and nostrils and two fangs, ¾″ to 1¼″ (2 to 3 cm) long. Because fangs may break off or grow behind old ones, some snakes may have one, three, or four fangs.

Because coral snakes are nocturnal and placid, their bites are less common than pit viper bites; pit vipers are also nocturnal but are more active. The fangs of coral snakes are short but have teeth behind them. Coral snakes have distinctive red, black, and yellow bands (yellow bands always border red ones), tend to bite with a chewing motion, and may leave multiple fang marks, small lacerations, and much tissue destruction.

Most snakebites happen on the arms and legs, below the elbow or knee. Bites to the head or trunk are most dangerous, but any bite into a blood vessel is dangerous, regardless of location.

Most pit viper bites that result in envenomation cause immediate and progressively severe pain and edema (the entire extremity may swell within a few hours), local elevation in skin temperature, fever, skin discoloration, petechiae, ecchymoses, blebs, blisters, bloody wound discharge, and local necrosis.

Because pit viper venom is neurotoxic, pit viper bites may cause local and facial numbness and tingling, fasciculation and twitching of skeletal muscles, seizures (especially in children), extreme anxiety, difficulty speaking, fainting, weakness, dizziness, excessive sweating, occasional paralysis, mild to severe respiratory distress, headache, blurred vision, marked thirst and, in severe envenomation, coma and death. Pit viper venom may also impair coagulation and cause hema-temesis, hematuria, melena, bleeding gums, and internal bleeding. Other
symptoms of pit viper bites include tachycardia, lymphadenopathy, nausea, vomiting, diarrhea, hypotension, and shock.

The reaction to coral snakebite is usually delayed—sometimes up to several hours. These snakebites cause little or no local tissue reaction (local pain, swelling, or necrosis). However, because coral snake venom is neurotoxic, a reaction can progress swiftly, producing such effects as local paresthesia, drowsiness, nausea, vomiting, difficulty swallowing, marked salivation, dysphonia, ptosis, blurred vision, miosis, respiratory distress and possible respiratory failure, loss of muscle coordination and, possibly, shock with cardiovascular collapse and death.

The patient’s history and account of the injury, observation of fang marks, snake identification (when possible), and progressive symptoms of envenomation all point to poisonous snakebite. Laboratory test results help identify the extent of envenomation and provide guidelines for supportive treatment.

Abnormal test results in poisonous snakebites may include the following: