Bungarus is a genus of venomous elapid snakes, the kraits ("krait" is pronounced //, rhyming with "kite"), found in South and Southeast Asia. There are 14 species and five subspecies (excluding nominal) recognized.
|Bungarus fasciatus (the largest species of krait)|
Kraits usually range between 1 and 1.5 m (3 ft 3 in and 4 ft 11 in) in length, although specimens as large as 2 m have been observed. The banded krait (B. fasciatus) may grow as large as 2.125 m (6 ft 11.7 in). Most species of kraits are covered in smooth, glossy scales arranged in bold, striped patterns of alternating black and light-colored areas. This may serve as aposematic colouration in its habitat of grassland and scrub jungle. The scales along the dorsal ridge of the back are hexagonal. The head is slender and the eyes have round pupils. Kraits have pronounced dorsolateral flattening, which causes them to be triangular in cross section. The tail tapers to a thin point.
Diet and behaviorEdit
All kraits are nocturnal. They are more docile during the daylight hours; at night, they become very active, but are not very aggressive even when provoked. They are actually rather timid, and will often hide their heads within their coiled bodies for protection. When in this posture, they will sometimes whip their tails around as a type of distraction.
Bungarus contains some species which are among the most venomous land snakes in the world to mice based on their LD50. They have highly potent neurotoxic venom which can induce muscle paralysis. Clinically, their venom contains mostly presynaptic neurotoxins. These affect the ability of neuron endings to properly release the chemical that sends the message to the next neuron. Following envenomation with bungarotoxins, transmitter release is initially blocked (leading to a brief paralysis), followed by a period of massive overexcitation (cramps, tremors, spasms), which finally tails off to paralysis. These phases may not be seen in all parts of the body at the same time. Since kraits are nocturnal, they seldom encounter humans during daylight hours, so bites are rare, but a bite from a krait is potentially life-threatening, and should be regarded as a medical emergency.
Typically, victims start to complain of severe abdominal cramps accompanied by progressive muscular paralysis, frequently starting with ptosis. As there are no local symptoms, a patient should be carefully observed for tell-tale signs of paralysis (e.g. the onset of bilateral ptosis, diplopia, and dysphagia), and treated urgently with antivenom. Frequently, little or no pain occurs at the site of a krait bite, which can provide false reassurance to the victim. The major medical difficulty of envenomated patients are the lack of medical resources (especially intubation supplies and mechanical ventilators in rural hospitals) and the ineffectiveness of the antivenom.
Once at a healthcare facility, support must be provided until the venom is metabolised and the victim can breathe unaided, especially if no species-specific antivenom is available. Given that the toxins alter acetylcholine transmission which causes the paralysis, some patients have been successfully treated with cholinesterase inhibitors, such as physostigmine or neostigmine, but success is variable and may be species-dependent, as well. If death occurs, it typically takes place about six to 12 hours after the krait bite, but can be significantly delayed. Cause of death is usually respiratory failure—suffocation by complete paralysis of the diaphragm. Even if patients make it to a hospital, subsequent permanent coma and even brain death from hypoxia may occur, given the potentially long transport times to get medical care.
Mortality rates caused by bites from the members of this genus vary from species to species; according to University of Adelaide Department of Toxicology, bites from the banded krait have an untreated mortality rate of 1–10%, while those of the common krait are 70–80%. Several websites state the mortality rate is 50% even with treatment, but no specific species is mentioned and no original source in the medical literature for this statement is given. In common with those of all other venomous snakes, the death time and fatality rate resulting from bites of kraits depend on numerous factors, such as the venom yield and the health status of the victim.
Polyvalent Elapid Antivenom is effective in neutralizing of the venoms of B. candidus and B. flaviceps and rather effective for B. fasciatus. In this last case, the monovalent B. fasciatus antivenom is also moderately effective.
|Species||Authority||Subsp.*||Common name||Geographic range|
|B. andamanensis||Biswas & Sanyal, 1978||0||South Andaman krait||India (Andaman Island)|
|B. bungaroides||(Cantor, 1839)||0||Northeastern hill krait||Myanmar, India (Assam, Cachar, Sikkim), Nepal, Vietnam|
|B. caeruleusT||(Schneider, 1801)||0||Common krait||Afghanistan, Pakistan, India (Bengal, Maharashtra, Karnataka), Sri Lanka, Bangladesh, Nepal|
|B. candidus||(Linnaeus, 1758)||0||Malayan krait, blue krait||Cambodia, Indonesia (Java, Sumatra, Bali, Sulawesi), Malaysia (Malaya), Singapore, Thailand, Vietnam|
|B. ceylonicus||Günther, 1864||1||Sri Lankan krait||Sri Lanka|
|B. fasciatus||(Schneider, 1801)||0||Banded krait||Bangladesh, Brunei, Myanmar, Cambodia, south China (incl. Hong Kong, Hainan), north-east India, Eturnagaram[Warangal[Telangana]India], Bhutan, Nepal, Indonesia (Sumatra, Java, Borneo), Laos, Macau; Malaysia (Malaya and East Malaysia), Singapore, Thailand, Vietnam and Philippines|
|B. flaviceps||(Reinhardt, 1843)||1||Red-headed krait||South Thailand, South Myanmar, Cambodia, Vietnam, Malaysian Peninsula, Pulau Tioman, Indonesia (Bangka, Sumatra, Java, Billiton, Borneo)|
|B. lividus||Cantor, 1839||0||Lesser black krait||India, Bangladesh, Nepal|
|B. magnimaculatus||Wall and Evans, 1901||0||Burmese krait||Myanmar|
|B. multicinctus||Blyth, 1861||1||Many-banded krait||Taiwan, south China (Hong Kong, Hainan), Myanmar, Laos, northern Vietnam, Thailand and northern Philippines|
|B. niger||Wall, 1908||0||Greater black krait||India (Assam, Sikkim), Nepal, Bangladesh, Bhutan|
|B. persicus||Abtin, Nilson, Mobaraki, Hosseini & Dehgannejhad, 2014||0||None||Iran|
|B. sindanus||Boulenger, 1897||2||Sind krait||Southeast Pakistan, India|
|B. slowinskii||Kuch et al., 2005||0||Red River krait||Northern Vietnam|
*) Not including the nominate subspecies (typical form).
T) Type species
Kraits have a reputation as deadly snakes and have figured in fiction as such.
Rudyard Kipling used a small sand-colored krait (in the story named Karait) as one of the three main villains in his short story "Rikki-Tikki-Tavi" (the other two villains being a pair of black cobras). In another Kipling short story, "The Return of Imray", a servant arrested for murder cheats the rope by stepping on a "karait".
Roald Dahl uses the krait as a device in his short story "Poison". A version of "Poison" is shown in Alfred Hitchcock Presents (TV series) October 5, 1958 and remade in Tales of the Unexpected (TV series) March 29, 1980.
The deadly snake in the Sherlock Holmes story "The Adventure of the Speckled Band" may have been a krait, although it is described in that work as an "Indian swamp adder". (The Russell's viper has also been considered as a possible culprit.)
In James Patterson's The 8th Confession, kraits are the murder weapons used by a serial killer.
In Michael Crichton's "Micro", a Banded Krait appears in captivity and is used in an attempt to kill one of the main characters.
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- Whitaker, Captain, Romulus, Ashok (2004). Snakes of India, The Field Guide. India: Draco Books. ISBN 81-901873-0-9.
- "Bungarus fasciatus". WCH Clinical Toxinology Resources.
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- Prof Tan, Nget Hong. "Antivenoms against Malaysian poisonous snakes". University of Malaya. Retrieved 2009-09-23.
- Kuch, U., D: Kizirian, Q.T. Nguyen, R. Lawson, M.A. Donnelly, & D. Mebs (2005). A new species of krait (Squamata: Elapidae) from the Red River System of Northern Vietnam. Copeia 2005(4): 818-833
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- Detailed account of Joe Slowinski's death via krait bite