Mambas are fast-moving, highlyvenomous snakes of thegenusDendroaspis (which literally means "treeasp") in the familyElapidae. Fourextant species are recognised currently; three of those four species are essentiallyarboreal and green in colour, whereas theblack mamba,Dendroaspis polylepis, is largely terrestrial and generally brown or grey in colour. All are native to various regions insub-Saharan Africa and all are feared throughout their ranges, especially the black mamba. In Africa there are many legends and stories about mambas.[2][3][4]
The three green species of mambas arearboreal, whereas theblack mamba is largely terrestrial. All four species are activediurnal hunters, preying onbirds,lizards, and smallmammals. At nightfall some species, especially the terrestrial black mamba, shelter in a lair. A mamba may retain the same lair for years. Resembling acobra, thethreat display of a mamba includes rearing, opening the mouth and hissing. The black mamba's mouth is black within, which renders the threat more conspicuous. A rearing mamba has a narrower yet longer hood and tends to lean well forward, instead of standing erect as a cobra does.
Stories of black mambas that chase and attack humans are common, but in fact the snakes generally avoid contact with humans.[5] The black mamba (Dendroaspis polylepis) is a highly venomous snake species native to various parts of sub-Saharan Africa. Black mambas are fast-moving, nervous snakes that will strike when threatened. According to findings by Branch (2016), their venom comprises neurotoxins and cardiotoxins that can rapidly induce symptoms, including dizziness, extreme fatigue, vision problems, foaming at the mouth, paralysis, convulsions, and eventual death from respiratory or cardiac failure if untreated. Although black mamba venom is highly toxic, antivenom is available and can treat envenomation promptly.
Most apparent cases of pursuit probably are examples of where witnesses have mistaken the snake's attempt to retreat to its lair when a human happens to be in the way.[6] The black mamba usually uses its speed to escape from threats, and humans actually are their main predators, rather than prey.[2]
There are multiple components in dendrotoxins with different targets:
Dendrotoxin 1, which inhibits the K+ channels at the pre and post-synaptic level in the intestinal smooth muscle. It also inhibits Ca2+-sensitive K+ channels from rat skeletal muscle‚ incorporated into planar bilayers (Kd = 90 nM in 50 mM KCl).[10])
Dendrotoxin K, structurally homologous to Kunitz-type proteinase inhibitors[12] with activity as a selective blocker of voltage-gated potassium channels[13]
Toxicity alone does not determine severity ofenvenomation; other factors include the snake's temperament, venom yields, proximity of wounds to theCNS and depth of punctures.[14] Bites by all members of this genus are capable of causing rapid onsets of symptoms, but it is the black mamba whosebite has the worst prognosis, possibly as a result of its more terrestrial nature (having more potential for human contact), high defensiveness (having a higher possibility to deliver fatal bites instead ofdry bites), large size (giving it a higher strike position proximal to the victim'sbrain), and higher average venom yields and potential toxicity (based onexperimental results).[15][16] A lethality rate of near 100% for untreated black mamba bites has been circulating between various sources,[16] which is probably based on a single medical record made in a single district between 1957 and 1963 when specificantivenom had yet to be introduced. Seven out of seven victims of this species who received non-specificpolyvalent antivenom, that had no effect on the species' toxins, succumbed to its bites.[5] However, another snakebite survey inSouth Africa reported a death rate of approximately 43% among those who received ineffective treatments (15 fatal cases out of 35 patients).[17] A mamba-specific antivenom was introduced in 1962, followed by a fully polyvalent antivenom in 1971; over this period, 5 out of 38 people in South Africa bitten by black mambas who received the antivenom died, according to the same report.[17] Since then, the number has significantly dropped with the widespread use of specific antivenom.[18][17]
Despite their fearsome reputation and often exaggerated notoriety, mamba envenomation occurs far less frequently than some other snakes', for instance thepuff adder.[16][5] Besides proximity to residences, behaviour of a given species is also a critical aspect when it comes to snakebite morbidities. Mambas are agile, usually fleeing from any confrontation with unambiguousthreat display which allows early recognition of the serpent, avoiding escalation in tension.[17]
Dendroaspis, is derived fromAncient Greekdéndron (δένδρον), meaning "tree",[19] andaspis (ασπίς), which is understood to mean "shield",[20] but also denotes "cobra" or simply "snake", in particular "snake with hood (shield)". ViaLatinaspis, it is the source of the English word "asp". In ancient texts,aspis or asp often referred to theEgyptian cobra (Naja haje), in reference to its shield-like hood.[21] The genus was first described by the German naturalistHermann Schlegel in 1848,[22] withElaps jamesonii as thetype species. It was misspelt asDendraspis by Dumeril in 1856, and generally uncorrected by subsequent authors. In 1936, Dutch herpetologistLeo Brongersma pointed out that the correct spelling wasDendroaspis but added that the name was invalid as Fitzinger had coinedDendraspis in 1843 for the king cobra and hence had priority.[23] However, in 1962 German herpetologistRobert Mertens proposed that the 1843 description ofDendraspis by Fitzinger be suppressed due to its similarity toDendroaspis, and the confusion it would cause by its use.[24]
Black mambas live in the savannas and rocky hills of southern and eastern Africa. They are Africa's longest venomous snake, reaching up to 14 feet in length, although 8.2 feet is more the average. They are also among the fastest snakes in the world, slithering at speeds of up to 12.5 miles per hour.[2][6]
A 2018 analysis of the venom of the mambas, as well as a 2016 genetic analysis, found the following cladogram representative of the relationship between the species.[26][27]
^Snakes of medical importance include those with highly dangerous venom resulting in high rates of morbidity and mortality, or those that are common agents in snakebite.[9]
^Abinomial authority in parentheses indicates that the species was originally described in a genus other thanDendroaspis.
^abcO'Shea, Mark (2005).VENOMOUS SNAKES OF THE WORLD. multiple places: US and Canada: Princeton University Press; Europe: New Holland (UK) Ltd. pp. 78–79.ISBN978-0-691-15023-9....in common with other snakes they prefer to avoid contact;...Of the three species of green mambas...;...from 1957 to 1963...including all seven black mamba bites - a 100 per cent fatality rate
^abThe new encyclopedia of Reptiles (Serpent). Time Book Ltd. 2002.
^Newitt RA, Houamed KM, Rehm H, Tempel BL (1991). "[Potassium channels and epilepsy: evidence that the epileptogenic toxin, dendrotoxin, binds to potassium channel proteins.]".Epilepsy Research Supplement.4:263–73.PMID1815606.
^abRang, H. P. (2003).Pharmacology. Edinburgh: Churchill Livingstone. p. 139.ISBN0-443-07145-4.
^Berndt KD, Güntert P, Wüthrich K (5 December 1993). "[Nuclear magnetic resonance solution structure of dendrotoxin K from the venom of Dendroaspis polylepis polylepis.]".Journal of Molecular Biology.234 (3):735–50.doi:10.1006/jmbi.1993.1623.PMID8254670.
^Harvey AL, Robertson B (2004). "Dendrotoxins: structure-activity relationships and effects on potassium ion channels".Curr. Med. Chem.11 (23):3065–72.doi:10.2174/0929867043363820.PMID15579000.
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