there are 3,971 known snake species worldwide, with around 600 venomous species. 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 region. While several species of snakes may cause more bodily harm than others, any one of these venomous snakes is still very capable of causing a human fatality should a bite go untreated, regardless of 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 for administering the LD50 test:
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, using mice. Subcutaneous is the most applicable to actual bites: Only large Bitis or extremely large Bothrops or Crotalus specimens are able to deliver a bite that is truly intramuscular, and intravenous injections are extremely rare in actual bites. Mixing dry venom with 0.1% bovine serum albumin in saline gives more consistent test results than mixing with 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 Due to ethical reasons, these studies are being superseded by in vitro studies.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".
+ World's most venomous snakesThe Australian venom research unit (January 11, 2014). Facts and Figures: World's Most Venomous Snakes (archived). University of Melbourne. Retrieved July 14, 2014.Fry, B. (February 24, 2012). "Snakes Venom LD50 – list of the available data and sorted by route of injection ". School of Biological Sciences, University of Queensland. Snake Region subcutaneous injection 0.1% bovine serum albumin in Saline subcutaneous injection Saline intravenous injection Inland taipan Inland, central Australia 0.01 mg/kg 0.025 mg/kg 0.013 mg/kg Dubois' sea snake Tropical oceanic watersN/A0.044 mg/kg N/A Eastern brown snake Australia, Papua New Guinea, Indonesia 0.041 mg/kg0.053 mg/kg0.01 mg/kg Yellow-bellied sea snake Tropical oceanic waters N/A 0.067 mg/kgN/ACentral Ranges taipanInland, central Australia N/A0.075 mg/kgN/A Peron's sea snake Gulf of Siam, Strait of Taiwan, Coral sea islands, and other places N/A 0.079 mg/kgN/A Coastal taipan Australia 0.064 mg/kg0.099 mg/kg0.013 mg/kg (0.002 mg/kg for pure taipoxin) Many-banded krait Hong Kong, Mainland China, Taiwan, Vietnam, Laos, Burma N/A 0.09 mg/kg0.113 mg/kg Black-banded sea krait Eastern coast of the Malay Peninsula and Brunei, and in Halmahera, Indonesia. N/A 0.111 mg/kgN/ABeaked sea snake Tropical Indo-Pacific 0.164 mg/kg0.1125 mg/kgN/A Black tiger snake Australia 0.099 mg/kg0.131 mg/kgN/A Western tiger snake Australia 0.124 mg/kg0.194 mg/kgN/A
Medically significant species
Mortality (often determined by measured toxicity on mice) is a commonly used indicator of the danger of any given venomous snake, but important too are efficiency of venom delivery, venom yield, and behavior upon encountering humans.Venomous Snakes. World's Deadliest Snakes – Ranking scale . Reptile Gardens. Retrieved October 18, 2013.Walls, Jerry G. (November 20, 2013). Deadly Snakes: What are the world's most deadly venomous snakes?. Reptiles (magazine). Retrieved November 5, 2013. Given these additional, practical concerns, many snake experts have cited the black mamba and the coastal taipan as the world's most dangerous snakes – even though their venoms, drop for drop, are not the most lethal. Both species are elapids, and in several aspects of morphology, ecology and behavior, the coastal taipan is strongly convergent with the black mamba.
Black mamba
The black mamba (Dendroaspis polylepis) is a large and highly venomous snake species native to much of Sub-Saharan Africa. It is the second-longest venomous snake species in the world and is the fastest-moving land snake, capable of moving at 4.3 to 5.4 metres per second (16–20 km/h, 10–12 mph). The black mamba is the most feared snake in Africa because of its size, aggression, venom toxicity and speed of onset of symptoms following envenomation, and is classified as a snake of medical importance by the World Health Organization.
This species of snake shows tenacity, fearlessness, and aggression when cornered or threatened, during breeding season, or when defending its territory. They are also known to have up to a 100% rate of envenomation; the probability of dry bites (no venom injected) in black mamba strikes is almost non-existent. The venom of the black mamba is a protein of low molecular weight and as a result is able to spread rapidly within the bitten tissue. The venom is the most rapid-acting venom of any snake species and consists mainly of highly potent neurotoxins;Reed, Tim; Eaton, Katie; Peng, Cathy and Doern, BettyLou. Neurotoxins in Snake Venom. California State University Stanislaus. csustan.edu. it also contains cardiotoxins, fasciculins, and calciseptine.
Based on the median lethal dose (LD50) values in mice, the black mamba LD50 from all published sources is as follows: (SC) subcutaneous (most applicable to real bites): 0.32 mg/kg,Fry, Bryan, Deputy Director, Australian Venom Research Unit, University of Melbourne (March 9, 2002). "Snakes Venom LD50 – list of the available data and sorted by route of injection ". venomdoc.com. (archived) Retrieved October 14, 2013.Sherman A. Minton, (May 1, 1974) Venom diseases, Page 116Philip Wexler, 2005, Encyclopedia of toxicology, Page 59 0.28 mg/kg.JERRY G. WALLS, The World's Deadliest Snakes, Reptiles (magazine) (IV) intravenous: 0.25 mg/kg, 0.011 mg/kg.Thomas J. Haley, William O. Berndt, 2002, Toxicology, Page 446 (IP) intraperitoneal: 0.30 mg/kg (average),Scott A Weinstein, David A. Warrell, Julian White and Daniel E Keyler (Jul 1, 2011) " Bites from Non-Venomous Snakes: A Critical Analysis of Risk and Management of "Colubrid" Snake Bites (page 246) 0.941 mg/kg. 0.05 mg/kg (the last quote does not make it clear if it is either intravenous or intraperitoneal).
It is estimated that only 10 to 15 mg will kill a human adult; however, its bites deliver about 120 mg of venom on average, although they may deliver up to 400 mg of venom in a single bite. Severe neurotoxicity invariably ensues rapidly. This is because of several factors, including the high potency of the venom, and the unusual composition of synergistic toxins contained within the venom, which bring on severe symptoms of envenomation and death much faster than any other snake venom. In addition, the snake itself possesses the most advanced, evolved, and efficient venom delivery apparatus among all venomous snakes, and the most advanced and evolved dentition of all elapids. Black mambas possess the longest fangs of any elapid, which average around , but may grow as long as . Another feature that distinguishes the dentition and venom delivery apparatus of this species from all other elapids, as well as other species of venomous snake including those of the family Viperidae, is that the fangs are positioned well forward at the most anterior position possible in its mouth – right up in the front of the upper jaw.
The proteins in black mamba venom are of low molecular weight, low viscosity, and the venom's high activity in terms of hyaluronidases, which is also essential in facilitating dispersion of venom toxins throughout tissue (spreading the venom through the body) by catalyzing the hydrolysis of hyaluronan, a constituent of the extracellular matrix (ECM), hyaluronidase lowers the viscosity of hyaluronan, and Dendroaspin natriuretic peptide (DNP), a newly discovered component of mamba venom, is the most potent natriuretic peptide and is unique to the genus Dendroaspis, or mambas. It is a polypeptide analogous to the human atrial natriuretic peptide; it is responsible for causing diuresis through natriuresis and dilating the vessel bloodstream, which results in, among other effects, acceleration of venom distribution in the body of the victim, thereby increasing tissue permeability. These advanced and highly evolved physical and biological features combined with this species' large size, explosive aggression, and quickness make the black mamba a terrifying adversary. Neurological, respiratory, and cardiovascular symptoms rapidly begin to manifest, usually within less than ten minutes. Common symptoms are rapid onset of dizziness, drowsiness, headache, coughing or difficulty breathing, convulsions, and an erratic heartbeat. Other common symptoms which come on rapidly include neuromuscular symptoms, shock, loss of consciousness, hypotension, pallor, ataxia, excessive salivation (oral secretions may become profuse and thick), limb paralysis, nausea and vomiting, ptosis, fever, and severe abdominal pain. Local tissue damage appears to be relatively infrequent and of minor severity in most cases of black mamba envenomation. Edema is typically minimal. Acute kidney injury has been reported in a few cases of black mamba bites in humans as well as in animal models. Death is due to suffocation resulting from paralysis of the respiratory muscles.
Untreated black mamba bites have a mortality rate of 100%. Antivenom therapy is the mainstay of treatment for black mamba envenomation. A polyvalent antivenom produced by the South African Institute for Medical Research (SAIMR) is used to treat all black mamba bites from different localities. Because of the availability of antivenom, a bite from a black mamba no longer results in certain death, but in order for the antivenom therapy to be successful, vigorous treatment and large doses of antivenom must be administered rapidly post-envenomation. In case studies of black mamba envenomation, respiratory paralysis has occurred in less than 15 minutes. Envenomation by this species invariably causes severe neurotoxicity because black mambas often strike repeatedly in a single lunge. The doses of antivenom required are often massive (10–30+ vials) for bites from this species. Although antivenom saves many lives, mortality due to black mamba envenomation is still at 14%, even with antivenom treatment. In addition to antivenom treatment, endotracheal intubation and mechanical ventilation are required for supportive therapy.
Coastal taipan