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Crotalus viridis
General Details, Taxonomy and Biology, Venom, Clinical Effects, Treatment, First Aid , Antivenoms
Crotalus viridis  ( Praire Rattlesnake  ) subsp.  viridis   [ Original photo copyright © Dr Julian White ]
Family: Viperidae
Subfamily: Crotalinae
Genus: Crotalus
Species: viridis
Subspecies: viridis
Common Names
( subsp. viridis ) Prairie Rattlesnake
Local Names
Cascabel de Pradera , Vibora de Cascabel
Region
North America + Central America
Countries
Canada, Mexico, United States of America
 
Taxonomy and Biology
Adult Length: 0.75 m
General Shape
Medium in length, medium bodied rattlesnake with a short tail and horn-like segmented rattle. Can grow to a maximum of about 1.45 metres. Head is large, short, very broad and rounded when viewed from above and very distinct from narrow neck. Eyes are moderately small in size with vertically elliptical pupils. Dorsal scales are keeled. Usually about 12 rattle fringe scales.
Habitat
Elevations up to about 3500 metres in desert, mesquite grassland and pine-oak forest.
Habits
Terrestrial and mainly diurnal snake with nocturnal tendencies during the hottest months.
Prey
Feeds on a wide variety of lizards, rodents, small mammals and birds.
Species Map
Small (Approx 20k) version
 
Venom
Average Venom Qty
50 to 100 mg ( dry weight ), Minton (1974) ( Ref : R000504 ).
General: Venom Neurotoxins
Unknown
General: Venom Myotoxins
Systemic myotoxins present
General: Venom Procoagulants
Mixture of procoagulants
General: Venom Anticoagulants
Probably not present
General: Venom Haemorrhagins
Zinc metalloproteinase
General: Venom Nephrotoxins
Probably not present
General: Venom Cardiotoxins
Probably not present
General: Venom Necrotoxins
Possibly present
General: Venom Other
May include; Lectins; Nerve growth factors; Phospholipase inhibitors; Proteinase inhibitors; Complement inactivators; Biogenic amines; Carbohydrates; Lipids; Nucleosides & nucleotides Other
 
Clinical Effects
General: Dangerousness
Clinical effects uncertain, but related to medically important species, therefore major envenoming cannot be excluded. Some subspecies have caused fatalities (Crotalus oreganus helleri).
General: Rate of Envenoming: Unknown but likely to be moderate
General: Untreated Lethality Rate: <1%Unknown but has caused deaths (Crotalus oreganus helleri)
General: Local Effects
Marked local effects possible; pain, severe swelling, bruising, blistering, necrosis (Crotalus oreganus helleri)
General: Local Necrosis
Potentially may occur
General: General Systemic Effects
Variable non-specific effects which may include headache, nausea, vomiting, abdominal pain, diarrhoea, dizziness, collapse or convulsions
General: Neurotoxic Paralysis
Unlikely to occur
General: Myotoxicity
No case reports for this species, but related species can cause systemic myolysis
General: Coagulopathy & Haemorrhages
Coagulopathy can occur, but it is unclear how severe it may be, though extensive haemorrhages have been found in fatal cases (Crotalus oreganus helleri)
General: Renal Damage
No case reports for this species, but related species can cause renal failure secondary to myolysis.
General: Cardiotoxicity
Unlikely to occur
General: Other
Shock secondary to fluid shifts due to local tissue injury is likely in severe cases
 
First Aid
Description: First aid for bites by Viperid snakes likely to cause significant local injury at the bite site (see listing in Comments section).
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.
 
Treatment
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.
Key Diagnostic Features
Variable severity local pain, swelling, blistering, ± necrosis. Systemic effects may include coagulopathy, bleeding, renal failure, rarely myolysis &/or mild paralysis
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.
Antivenom Therapy
Antivenom is the key treatment for systemic envenoming. Multiple doses may be required.
Antivenoms
1. Antivenom Code: SAmPRO01
Antivenom Name: Polyvalent crotalid antivenom ( CroFab ), Ovine, Fab
Manufacturer: Protherics Inc. (US)
Phone: ++1-615-327-1027
Address: 5214 Maryland Way
Suite 405
Brentwood
Tennessee 37027
USA
Country: U.S.A.
2. Antivenom Code: SAmIBM06
Antivenom Name: Antivipmyn
Manufacturer: Instituto Bioclon
Phone: ++56-65-41-11
Address: Calzada de Tlalpan No. 4687
Toriello Guerra
C.P. 14050
Mexico, D.F.,
Country: Mexico
Crotalus viridis ( Praire Rattlesnake ) subsp. viridis [ Original photo copyright © Dr Julian White ]
Larger version
 
Crotalus viridis ( Prairie Rattlesnake ) subsp. viridis [ Original photo copyright © Dr Julian White ]
Larger version
 
Crotalus viridis ( Prairie Rattlesnake ) subsp. viridis [ Original photo copyright © Dr Julian White ]
Larger version
 
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