As of 2022, there are 3,971 snake species, there are around 600 venomous snake species in the world, and about 200 are able to kill a human. This is an overview of the snakes that pose a significant health risk to humans, through snakebites or other physical trauma. The varieties of snakes that most often cause serious snakebites depend on the region of the world. In Africa, the most dangerous species include black mambas, puff adders, and carpet vipers. In the Middle East the species of greatest concern are carpet vipers and elapids; in Central and South America, Bothrops (including the terciopelo or fer-de-lance) and Crotalus (rattlesnakes) are of greatest concern. In South Asia, it has historically been believed that Indian cobras, common kraits, Russell's viper and carpet vipers were the most dangerous species; however other snakes may also cause significant problems in this area of the world. While several species of snakes may cause more bodily destruction than others, any of these venomous snakes are still very capable of causing human fatalities should a bite go untreated, regardless of their venom capabilities or behavioral tendencies. Most venomous species The median lethal dose (LD50) of a venom is the dose required to kill half the members of a tested population after a specified test duration. A lower LD50 number indicates increased toxicity. There are four methods in which the LD50 test is measured: Subcutaneous: Venom is injected into the fatty layer beneath the skin. Intravenous: Venom is injected directly into a vein. Intramuscular: Venom is injected into a muscle. Intraperitoneal: Venom is injected into the abdominal cavity. The most commonly tested methods are subcutaneous and intravenous injections of mice. Subcutaneous is the most applicable to actual bites. Only large Bitis or extremely large Bothrops or Crotalus specimens would be able to deliver a bite that is truly intramuscular. Intravenous injections are extremely rare in actual bites. Testing using dry venom mixed with 0.1% bovine serum albumin in saline, gives more consistent results than just saline alone. Wayne C Hodgson et al. stated in 2002: "Historically, the lethality of snake venoms has been based on murine LD50 studies. Due to ethical reasons, these studies are being superseded by in vitro studies. Instead, the time taken to produce 90% inhibition of nerve-mediated twitches (i.e. t90) in skeletal muscle preparations can be determined.". Medically significant species Mortality (often determined by measured toxicity on