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Naja is a genus of venomous elapid snakes known as cobras. Several other genera include species commonly called cobras (for example the rinkhals, or ring-necked spitting cobra [Hemachatus haemachatus]), but of all the snakes known by that name, members of the genus Naja are the most widespread and the most widely recognized as cobras. Various species occur in regions throughout Africa, Southwest Asia, South Asia and Southeast Asia.

Until recently the genus Naja had 20 to 22 species, but it has undergone several taxonomic revisions in recent years, so sources vary greatly. There is however wide support for a 2009 revision that synonymised the genera Boulengerina and Paranaja with Naja. According to that revision the genus Naja now includes 28 species.

Etymology


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The origin of this genus name is from the Sanskrit nāga (with a hard "g") meaning "snake". Some hold that the Sanskrit word is cognate with English "snake", Germanic: *snÄ"k-a-, Proto-IE: *(s)nÄ"g-o-, but this is unlikely. Mayrhofer calls this etymology "unglaubhaft ", "not credible", and suggests a more plausible etymology connecting it with Sanskrit nagna, "hairless, naked".

Description


Naja

Different Naja species vary in length and most are relatively slender-bodied snakes. Most species are capable of attaining lengths of 1.84 m (6.0 ft). Maximum lengths for some of the larger species of cobra are around 3.1 m (10 ft), with the forest cobra arguably being the longest species. All have a characteristic ability to raise the front quarters of their bodies off the ground and flatten their necks to appear larger to a potential predator.

Venom


Naja

All species in the genus Naja are capable of delivering a fatal bite to a human. Most species have strongly neurotoxic venom, which attacks the nervous system, causing paralysis, but many also have cytotoxic features which causes swelling and necrosis, and has a significant anticoagulant effect. Some also have cardiotoxic components to their venom.

Several Naja species, referred to as spitting cobras, have a specialized venom delivery mechanism, in which their front fangs, instead of releasing venom through the tips (similar to a hypodermic needle), have a rifled opening in the front surface which allows the snake to propel the venom out of the mouth. While typically referred to as "spitting", the action is more like squirting. The range and accuracy with which they can shoot their venom varies from species to species, but it is used primarily as a defense mechanism. Once sprayed onto a victim's skin, the venom acts as a severe irritant. If it is introduced to the eye, it can cause a severe burning sensation and temporary or even permanent blindness if not cleaned out immediately and thoroughly.

Contrary to popular belief, the Philippine cobra (N. philippinensis) is not the most venomous Naja species. The Caspian cobra (N. oxiana) of Central Asia produces a more toxic venom. The average subcutaneous LD50 for N. oxiana in mice is 0.18 mg/kg, and the lowest reported value for N. oxiana is 0.10 mg/kg SC. while N. philippinensis has an average murine LD50 of 0.2 mg/kg SC. The lowest value reported for N. philippinensis is 0.14 mg/kg SC. In mice, the IV LD50 for the Caspian cobra it's 0.037 mg/kg, and for the Philippine cobra it's 0.05 mg/kg. The Caspian cobra is the most venomous species of cobra in the world. The crude venom of N. oxiana produced the lowest known lethal dose (LCLo) of 0.005 mg/kg, the lowest among all cobra species ever recorded, derived from an individual case of poisoning by intracerebroventricular injection. After the Caspian cobra and the Philippine cobra, is the Forest cobra with a LD50 of 0.225 mg/kg SC, followed by the Samar cobra (N. samarensis) which has a value of 0.23 mg/kg SC. The water cobras of central Africa are also highly venomous. The murine intraperitoneal LD50 of Naja annulata and Naja christyi venoms were 0.143 mg/kg and 0.120 mg/kg, respectively.

The Naja species are a medically important group of snakes due to the number of bites and fatalities they cause across their geographical range. They range throughout Africa (including some parts of the Sahara where Naja haje can be found), Southwest Asia, Central Asia, South Asia, East Asia, and Southeast Asia. But unlike some other members of the Elapidae family (the species of the genus Bungarus, genus Oxyuranus, genus Pseudohaje, and especially genus Dendroaspis), the majority of bites by both African and Asian species of the genus Naja are "dry bites" (a dry bite is a bite by venomous snake which does not inject venom). Roughly 45-50% (sometimes more) of bites by most cobra species are dry bites and thus don't cause envenomation. Some of the species which are well known and documented to not envenomate in a bite include: Naja naja, Naja kaouthia, Naja sputatrix, Naja siamensis, Naja haje, Naja annulifera, Naja anchietae and Naja nigricollis. Some species will inject venom in many of their bites, but still have a high number of bites which don't envenomate and some of those species include: Naja sumatrana, Naja melanoleuca, Naja atra, Naja mossambica and Naja katiensis. Among the genus, there are a few species in which "dry bites" are very rare. Envenoming occurs in more than 80% of bite cases among bites by these species. The species which typically inject venom in almost all their bites include some of the more dangerous and venomous species of this genus: Naja oxiana, Naja philippinensis, Naja nivea, and Naja samarensis. There are many more species within the genus which have not yet been subject to much research and studies, and as a result, very little is known about their behaviour, venom, diet, habitat and general temperaments. Some of these species include Naja sagittifera, Naja annulata, Naja christyi and many others.

There are many factors which influence the differences in cases of fatality among different species within the same genus. Among cobras, the cases of fatal outcome of bites in both treated and untreated victims can be quite vast. For example, mortality rates among untreated cases of envenomation by the cobras as a whole group ranges from 6.5-20% for Naja naja to about 80% for Naja oxiana. Mortality rate for Naja atra is between 15-20%, 5-10% for Naja nigricollis, 50% for Naja nivea, 65-70% for Naja melanoleuca, 7-13% for Naja kaouthia, and 55-60% for Naja samarensis. In cases where victims of cobra bites that are medically treated using normal treatment protocol for elapid type envenomation also show differences in prognosis depending on the cobra species involved. The vast majority of envenomated patients treated make quick and complete recovery, while other envenomated patients who receive similar treatment result in fatality. The most important factors in the difference of mortality rates among victims envenomated by cobras is the severity of the bite and which cobra species caused the envenomation. Species like the Caspian cobra (N. oxiana) and the Philippine cobra (N. philippinensis) are the two cobra species with the most toxic venoms based on LD50 studies on mice. Both species cause prominent neurotoxicity and progression of life-threatening symptoms following envenomation by either species is rapid. Death has been reported in as little as 30 minutes in cases of envenomation by both species. N. philippinensis has a purely neurotoxic venom that causes prominent neurotoxicity with minimal local tissue damage and pain and patients respond very well to antivenom therapy if treatment is administered rapidly post-envenomation. Envenomation caused by N. oxiana is much more complicated. In addition to prominent neurotoxicity, there are very potent cytotoxic and cardiotoxic components in the species' venom. Local effects are marked and manifest in all cases of envenomation. There's severe pain, severe swelling, bruising, blistering, and tissue necrosis. Renal damage and cardiotoxicity are also clinical manifestations of envenomation causedu by N. oxiana, though they are rare and secondary. The untreated mortality rate among those envenomed by Naja oxiana approach 80%, the highest among all species within the genus Naja. Antivenom is not as effective for envenomation by this species as it is for other Asiatic cobras within the same region, like the Indian cobra (Naja naja) and due to the dangerous toxicity of this species' venom, massive amounts of antivenom are often required for patients. As a result, a monovalent antivenom serum is being developed by the Razi Vaccine and Serum Research Institute in Iran. Response to treatment with antivenom is generally poor among patients, so mechanical ventilation and endotracheal intubation is required. As a result, mortality among those treated for N. oxiana envenomation is still relatively high (up to 30%) compared to all other species of cobra (<1%).

Taxonomy


Naja

The genus contains several species complexes of closely related and often similar species, some of them only recently described or defined. Several recent taxonomic studies have revealed species not included in the current listing in ITIS:

  • Naja anchietae (Bocage, 1879), or Anchieta's cobra, is regarded as a subspecies of N. haje by Mertens (1937) and of N. annulifera by Broadley (1995). It is regarded as a full species by Broadley and Wüster (2004).
  • Naja arabica Scortecci, 1932, the Arabian cobra, has long been considered a subspecies of N. haje, but was recently raised to the status of species.
  • Naja ashei Broadley and Wüster, 2007, Ashe's spitting cobra, is a newly described species found in Africa.
  • Naja nigricincta Bogert, 1940, was long regarded as a subspecies of N. nigricollis, but was recently found to be a full species (with N. n. woodi as a subspecies).
  • Naja senegalensis Trape et al., 2009, is a new species encompassing what were previously considered to be the West African savanna populations of N. haje.

Two recent molecular phylogenetic studies have also supported the incorporation of the species normally assigned to the genera Boulengerina and Paranaja into Naja, as both are closely related to the forest cobra (Naja melanoleuca).

Wallach et al. suggested recognition of four subgenera within Naja: Naja for the Asiatic cobras, Boulengerina for the African forest, water and burrowing cobras, Uraeus for the Egyptian and Cape cobra group and Afronaja for the African spitting cobras.

Species

* Not including the nominate subspecies.
† Extinct.
T Type species.

References


Naja

External links



  • Naja at the Reptarium.cz Reptile Database. Accessed 13 April 2007.


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