Copperheads, and to a lesser extent cottonmouths, account for most other poisonous snake bites. Coral snakes inflict less than 1 percent of all bites. Imported snakes found in zoos, snake farms, and amateur or professional collections account for about 15 bites a year. A poisonous snake bite doesn't always result in snake venom poisoning. Venom is not injected in about 25 percent of all pit viper bites and about 50 percent of cobra and coral snake bites.
Snake venom is a complex mixture containing many proteins that trigger harmful reactions.
Snake venom can affect every major organ system in the body directly or indirectly. The venom of rattlesnakes and other pit vipers damages tissue around the bite, produces changes in blood cells, prevents blood from clotting, and damages blood vessels, causing them to leak. These changes can lead to internal bleeding and heart, respiratory, and kidney failure. The venom of coral snakes affects nervous system activity but causes little damage to tissue around the bite. The symptoms of pit viper poisoning vary widely, depending on the size and species of snake, the amount and toxicity of the venom injected, the bite's location, the victim's age and size, and the presence of other medical problems.