They are a significant cause of envenoming amongst fisherman in the Indian and Pacific oceans. Side fanged vipers of the Family Atractaspidae are confined to Africa and the Middle East. They have unusual fang structure and venoms, which contain endothelin like compounds called sarafotoxins, causing potent smooth muscle contraction. Vipers constitute the Family Viperidae. Venom glands are also typically larger than in other groups.
Vipers are a major cause of snakebite in the Americas, Africa, Europe and Asia.