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Family: Viperidae
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Subfamily: Crotalinae
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Genus: Crotalus
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Species: molossus
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Subspecies: nigrescens
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Common Names
( subsp. nigrescens ) Mexican Black-tailed Rattlesnake
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Local Names
Palanca , Tecutlacotzauhqui , Tepecolcoatl , Teuhtlacotzauhqui , Tleua , Vibora , Vibora de cascabel , Vibora de Cascabel de Cola Negra , Vibora de Cascabel de Colinegra
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Region
Central America
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Countries
Mexico
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Taxonomy and Biology
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Adult Length: 0.70 m
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General Shape
Medium in length, stout bodied rattlesnake with a short tail and horn-like segmented rattle. Can grow to a maximum of about 1.20 metres. Head is large, broad, rounded triangular when viewed from above, and very distinct from narrow neck. Eyes are moderately small in size with vertically elliptical pupils. Dorsal scales are keeled.
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Habitat
Elevations up to about 2600 metres in desert, chaparral, thorn forest, mesquite grassland, tropical deciduous forest, pine-oak forest and boreal forest.
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Habits
Mainly a diurnal and terrestrial snake during spring and autumn but with nocturnal tendencies during summer.
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Prey
Feeds mainly on lizards, rodents, small mammals and birds.
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Venom
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General: Venom Neurotoxins
Unknown
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General: Venom Myotoxins
Unknown
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General: Venom Procoagulants
Mixture of procoagulants
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General: Venom Anticoagulants
Not present
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General: Venom Haemorrhagins
Zinc metalloproteinase
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General: Venom Nephrotoxins
Unknown
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General: Venom Cardiotoxins
Unknown
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General: Venom Necrotoxins
Unknown
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General: Venom Other
Unknown
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Clinical Effects
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General: Dangerousness
Severe envenoming possible, potentially lethal
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General: Rate of Envenoming: Unknown but likely to be moderate
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General: Untreated Lethality Rate: Unknown but lethal potential cannot be excluded
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General: Local Effects
Marked local effects; pain, severe swelling, bruising, blistering
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General: Local Necrosis
Potentially may occur
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General: General Systemic Effects
Variable non-specific effects which may include headache, nausea, vomiting, abdominal pain, diarrhoea, dizziness, collapse or convulsions
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General: Neurotoxic Paralysis
Does not occur, based on current clinical evidence
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General: Myotoxicity
Insufficient clinical reports to know, but unlikely to occur
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General: Coagulopathy & Haemorrhages
Can occur, but frequency is uncertain, severity usually mild to moderate, without pathologic bleeding
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General: Renal Damage
Insufficient clinical reports to know
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General: Cardiotoxicity
Insufficient clinical reports to know, but unlikely to occur
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General: Other
Shock secondary to fluid shifts due to local tissue injury is likely in severe cases
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First Aid
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Description: First aid for bites by Viperid snakes likely to cause significant local injury at the bite site (see listing in Comments section).
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Details
1. After ensuring the patient and onlookers have moved out of range of further strikes by the snake, the bitten person should be reassured and persuaded to lie down and remain still. Many will be terrified, fearing sudden death and, in this mood, they may behave irrationally or even hysterically. The basis for reassurance is the fact that many venomous bites do not result in envenoming, the relatively slow progression to severe envenoming (hours following elapid bites, days following viper bites) and the effectiveness of modern medical treatment.
2. The bite wound should not be tampered with in any way. Wiping it once with a damp cloth to remove surface venom is unlikely to do much harm (or good) but the wound must not be massaged.
3. All rings or other jewellery on the bitten limb, especially on fingers, should be removed, as they may act as tourniquets if oedema develops.
4. The bitten limb should be immobilised as effectively as possible using an extemporised splint or sling; if available, crepe bandaging of the splinted limb is an effective form of immobilisation.
5. If there is any impairment of vital functions, such as problems with respiration, airway, circulation, heart function, these must be supported as a priority. In particular, for bites causing flaccid paralysis, including respiratory paralysis, both airway and respiration may be impaired, requiring urgent and prolonged treatment, which may include the mouth to mask (mouth to mouth) technique of expired air transfer. Seek urgent medical attention.
6. Do not use Tourniquets, cut, suck or scarify the wound or apply chemicals or electric shock.
7. Avoid peroral intake, absolutely no alcohol. No sedatives outside hospital. If there will be considerable delay before reaching medical aid, measured in several hours to days, then give clear fluids by mouth to prevent dehydration.
8. If the offending snake has been killed it should be brought with the patient for identification (only relevant in areas where there are more than one naturally occurring venomous snake species), but be careful to avoid touching the head, as even a dead snake can envenom. No attempt should be made to pursue the snake into the undergrowth as this will risk further bites.
9. The snakebite victim should be transported as quickly and as passively as possible to the nearest place where they can be seen by a medically-trained person (health station, dispensary, clinic or hospital). The bitten limb must not be exercised as muscular contraction will promote systemic absorption of venom. If no motor vehicle or boat is available, the patient can be carried on a stretcher or hurdle, on the pillion or crossbar of a bicycle or on someone's back.
10. Most traditional, and many of the more recently fashionable, first aid measures are useless and potentially dangerous. These include local cauterization, incision, excision, amputation, suction by mouth, vacuum pump or syringe, combined incision and suction ("venom-ex" apparatus), injection or instillation of compounds such as potassium permanganate, phenol (carbolic soap) and trypsin, application of electric shocks or ice (cryotherapy), use of traditional herbal, folk and other remedies including the ingestion of emetic plant products and parts of the snake, multiple incisions, tattooing and so on.
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Treatment
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Treatment Summary
Rattlesnake bites can cause major, even fatal envenoming. All cases require urgent assessment and management. For larger species, about 20% will have an ineffective bite, with no local or systemic envenoming, so will not require antivenom and may not require prolonged observation. This figure will be higher for the smaller species, which are generally unlikely to cause a severe bite. All other cases, with any degree of local or systemic effects, require extended observation and may require IV antivenom (Crofab), the amount partly dictated by the severity grading. Beware fluid shifts causing shock, coagulopathy and bleeding, kidney damage and necrosis of the bitten area.
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Key Diagnostic Features
Variable severity local pain, swelling, blistering, ± necrosis. Systemic effects may include coagulopathy, bleeding, renal failure, rarely myolysis &/or mild paralysis
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General Approach to Management
All cases should be treated as urgent & potentially lethal. Rapid assessment & commencement of treatment including appropriate antivenom (if indicated & available) is mandatory. Admit all cases.
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Antivenom Therapy
Antivenom is the key treatment for systemic envenoming. Multiple doses may be required.
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| 1. Antivenom Code: SAmPRO01
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Antivenom Name: Polyvalent crotalid antivenom ( CroFab ), Ovine, Fab
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Manufacturer: Protherics Inc. (US)
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Phone: ++1-615-327-1027
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Address: 5214 Maryland Way
Suite 405
Brentwood
Tennessee 37027
USA
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Country: U.S.A.
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| 2. Antivenom Code: SAmIBM06
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Antivenom Name: Antivipmyn
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Manufacturer: Instituto Bioclon
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Phone: ++56-65-41-11
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Address: Calzada de Tlalpan No. 4687
Toriello Guerra
C.P. 14050
Mexico, D.F.,
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Country: Mexico
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