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![Crotalus basiliscus ( Mexican West Coast Rattlesnake ) [ Original photo copyright © Dr Jurg Meier ]](images/snakes/SNP04201.jpg)
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Family: Viperidae
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Subfamily: Crotalinae
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Genus: Crotalus
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Species: basiliscus
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Common Names
Mexican West Coast Rattlesnake
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Local Names
Saye , Tepocolcoatl , Teuhtlacozauhqui , Vibora de Cascabel
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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: 1.25 m
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General Shape
Large in length, heavy, moderately stout and somewhat triangular cross sectional bodied rattlesnake with a short tail and horn-like segmented rattle. Older or larger specimens have a prominent spinal ridge on the anterior of the body. Can grow to a maximum of about 2.05 metres. Head is large, broad and very distinct from narrow neck. Eyes are moderately small in size with vertically elliptical pupils. Dorsal scales are strongly keeled. A prominent vertebral ridge is present on the anterior body in older ( large ) specimens.
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Habitat
Elevations up to about 600 metres in the northern portion of its range but as high as 2400 metres in the southern portion. Coastal plains, foothills and valleys with thorn forest, tropical deciduous forest and pine-oak forest.
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Habits
Terrestrial and diurnal snake.
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Prey
Feeds on a wide variety of small mammals.
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Venom
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Average Venom Qty
250 to 350 mg ( dry weight ), Minton (1974) ( Ref : R000504 ).
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General: Venom Neurotoxins
Possibly present
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General: Venom Myotoxins
Possibly present
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General: Venom Procoagulants
Mixture of procoagulants
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General: Venom Anticoagulants
Unknown
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General: Venom Haemorrhagins
Present but not defined
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General: Venom Nephrotoxins
Secondary nephrotoxicity only
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General: Venom Cardiotoxins
Not present
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General: Venom Necrotoxins
Secondary necrotoxic activity only
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General: Venom Other
May include; Lectins; Nerve growth factors; Phospholipase inhibitors; Proteinase inhibitors; Complement inactivators; Biogenic amines; Carbohydrates; Lipids; Nucleosides & nucleotides
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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: 20-40%
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General: Untreated Lethality Rate: 10-20%
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General: Local Effects
Insufficient clinical reports to know, but most likely minor local pain & swelling only
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General: Local Necrosis
Insufficient clinical reports to know
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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
No clinical reports for this species, but related species cause flaccid paralysis
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General: Myotoxicity
No case reports for this species, but related species can cause systemic myolysis
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General: Coagulopathy & Haemorrhages
No reports of coagulopathy, though related species can cause bleeding problems
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General: Renal Damage
Recognised complication, usually secondary to myolysis
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General: Cardiotoxicity
Unlikely to occur
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General: Other
Insufficient clinical reports to know
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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
Bites by species showing the South American rattlesnake clinical pattern are quite different from North American rattlesnake bites. The bite may cause few if any local effects, but can cause severe, even lethal systemic effects, particularly paralysis & myolysis (coagulopathy also possible). Therefore every case must be admitted at least overnight and closely observed. Should any evidence of paralysis or myolysis develop, antivenom is the principal treatment. Specific antivenoms exist for several major species.
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Key Diagnostic Features
Minimal to mild local reaction + flaccid paralysis, myolysis, sometimes coagulopathy & bleeding
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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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