Snake venom is merely modified saliva, or a combination of many different proteins and enzymes. Bites by poisonous snakes, also referred to as snake envenomization, cause thousands of deaths in dogs every year. Two major venomous snakes, species in the US, Crotalidae and Elapidae, are responsible for majority of snake bites.
One of the two primary snake families is crotalidate. It includes many species of the snakes such as Crotalus (rattlesnakes), Sistrurus (pigmy rattlesnakes and massassauga), and Agkistrodon (copperheads and cottonmouth water moccasins). These snakes have broad triangular heads with elliptical pupils, prominent curving fangs and a deep pit located between the nostril and the eye. For this reason they are commonly called "pit vipers."
Not all bites of venomous snakes contain poison. The risk of snakebite toxicity is based on the type of snake, the size of the animal bitten and the amount of venom injected in the bite.
Venom toxicity causes blood poisoning (hematoxicity) in the victim. Poison of many species attacks nervous system of the victim. The general ranking of severity is: (1) rattlesnakes, (2) moccasins, (3) copperheads.
The venom causes damage in the tissue around the bite. It may produce changes in blood cells, prevent blood from clotting, and damage blood vessels, causing them to leak. These changes can lead to internal bleeding and to heart, respiratory, and kidney failure.
Common symptoms associated with pit viper bites include
Local tissue swelling and pain surrounding bite site
Bruising, with possible dead tissue and sloughing at bite site
Red patches and spots on tissues and mucous membranes
Rapid heart beat
Depression and lethargy
Low blood pressure and shock