Mojave Rattlesnake Envenomation

Mojave Rattlesnake Envenomation

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Envenomation by some rattlesnakes, such as the Mojave rattlesnake (formerly Mohave rattlesnake) (Crotalus scutulatus), may cause a different clinical presentation than that generally encountered after most rattlesnake bites. In addition, other species, such as the Southern Pacific rattlesnake Crotalus oreganus helleri, (formerly Crotalus viridis helleri), may cause signs and symptoms consistent with typical rattlesnake envenomation combined with signs and symptoms similar to Mojave rattlesnake envenomation. [1] (See Rattlesnake Envenomation for a more complete discussion of typical rattlesnake envenomation.)

Mojave rattlesnakes inhabit desert areas of the southwestern United States and central Mexico. Specimens with type A venom, which cause a different pattern of injury than other rattlesnakes, have been reported in southern California, Nevada, Utah, Arizona, Texas, and New Mexico. [2, 3, 4, 5] Populations with venom B and intergrades of types A and B venom have been found in south-central Arizona, around Phoenix and Tucson. [6]

The Mojave rattlesnake may be difficult to distinguish from the western diamondback rattlesnake (Crotalus atrox), which inhabits an overlapping geographical range. Some Mojave rattlesnakes are greenish, but they may have a similar color as western diamondbacks. In the Mojave rattlesnake, the diamond pattern fades into bands along the caudal third of the back, whereas the diamonds continue to the tail in the western diamondback.

The Mojave rattlesnake’s white rings encircling the tail are much wider than the narrow black rings, whereas western diamondbacks have much more predominant black rings. The postocular stripe extends posteriorly above the mouth in the Mojave but intersects the corner of the mouth in the western diamondback. In Mojave rattlesnakes, supraocular scales are separated by fewer than 4 scales at their closest point. In western diamondbacks, at least 4 scales (usually >4) separate the supraocular scales.

See the image below.

Other rattlesnakes in the Mojave rattlesnake’s range and niche are distinguishable by the absence of a dorsal diamond pattern with light margins, black and white tail rings, facial stripes, or by the same criteria used to distinguish Mojave rattlesnakes from western diamondbacks.

Venom A populations of Mojave rattlesnakes possess Mojave toxin, which has been experimentally shown to induce neurotoxic effects. Mojave toxin or a similar toxin has been detected in the venom of other rattlesnake species. This toxin impairs presynaptic acetylcholine release. Mojave toxin may cause severe neurologic effects clinically, although this presentation has been reported only a few times in the literature. Envenomation by several other species of rattlesnakes has been reported to cause serious neurologic signs and symptoms (eg, severe motor weakness, respiratory difficulty).

Venom A Mojave rattlesnakes cause less local injury and less hemorrhagic/proteolytic effects than other rattlesnakes. In contrast, venom B specimens cause local, proteolytic, and hemorrhagic effects typical of other rattlesnakes. Severe rhabdomyolysis with myoglobinuric renal failure has been reported with Mojave rattlesnake envenomation. [7, 8, 9] This article focuses mainly on envenomation by venom A populations of Mojave rattlesnakes.

A large percentage of bites occur when the snake is handled, kept as a pet, or abused. These bites are considered intentionally interactive.

Males are bitten more commonly than females.

Young adults are most commonly bitten.

Full recovery is usually anticipated. Before antivenom, estimates of mortality rates ranged from 5-25%. Because of the development of antivenom, rapid EMS transport, and emergency/intensive care, mortality rates have improved to 0.28% (or better) when antivenom is administered and to 2.6% when antivenom is not administered.

Mojave toxin is one of the most lethal venom components found in US snakes. Venom B populations are less lethal than venom A populations. At least one death has been attributed to a Mojave rattlesnake in the Annual Report of the American Association of Poison Control Centers, although a number of deaths have been documented. [10, 11]  Most documented deaths are associated with bites in which the bitten individual was intentionally interacting with the snake and when a delay occurred in seeking medical care.

Call professionals, such as animal control, to move snakes (if it is necessary to move the snake). Never attempt to handle, possess, or kill venomous reptiles. For patient education resources, see the patient education article Snakebite.

French WJ, Hayes WK, Bush SP, Cardwell MD, Bader JO, Rael ED. Mojave toxin in venom of Crotalus helleri (Southern Pacific Rattlesnake): molecular and geographic characterization. Toxicon. 2004 Dec 1. 44(7):781-91. [Medline].

Farstad D, Thomas T, Chow T, Bush S, Stiegler P. Mojave rattlesnake envenomation in southern California: a review of suspected cases. Wilderness Environ Med. 1997 May. 8(2):89-93. [Medline].

Hardy DL. Envenomation by the Mojave rattlesnake (Crotalus scutulatus scutulatus) in southern Arizona, U.S.A. Toxicon. 1983. 21(1):111-8. [Medline].

Hardy DL. Fatal rattlesnake envenomation in Arizona: 1969-1984. J Toxicol Clin Toxicol. 1986. 24(1):1-10. [Medline].

Wingert WA, Chan L. Rattlesnake bites in southern California and rationale for recommended treatment. West J Med. 1988 Jan. 148(1):37-44. [Medline].

Glenn JL, Straight RC. Intergradation of two different venom populations of the Mojave rattlesnake (Crotalus scutulatus scutulatus) in Arizona. Toxicon. 1989. 27(4):411-8. [Medline].

Bush SP, Jansen PW. Severe rattlesnake envenomation with anaphylaxis and rhabdomyolysis. Ann Emerg Med. 1995 Jun. 25(6):845-8. [Medline].

Bush SP, Jansen PW. Severe rattlesnake envenomation with anaphylaxis and rhabdomyolysis. Ann Emerg Med. 1995 Jun. 25(6):845-8. [Medline].

Jansen PW, Perkin RM, Van Stralen D. Mojave rattlesnake envenomation: prolonged neurotoxicity and rhabdomyolysis. Ann Emerg Med. 1992 Mar. 21(3):322-5. [Medline].

Bronstein AC, Spyker DA, Cantilena LR Jr, Green J, Rumack BH, Heard SE. 2006 Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS). Clin Toxicol (Phila). 2007 Dec. 45(8):815-917. [Medline].

Gummin DD, Mowry JB, Spyker DA, Brooks DE, Fraser MO, Banner W. 2016 Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS): 34th Annual Report. Clin Toxicol (Phila). 2017 Dec. 55 (10):1072-1252. [Medline].

Massey DJ, Calvete JJ, Sánchez EE, Sanz L, Richards K, Curtis R, et al. Venom variability and envenoming severity outcomes of the Crotalus scutulatus scutulatus (Mojave rattlesnake) from Southern Arizona. J Proteomics. 2012 May 17. 75(9):2576-87. [Medline].

Carroll RR, Hall EL, Kitchens CS. Canebrake rattlesnake envenomation. Ann Emerg Med. 1997 Jul. 30(1):45-8. [Medline].

Bush SP. Snakebite suction devices don’t remove venom: they just suck. Ann Emerg Med. 2004 Feb. 43(2):187-8. [Medline].

Bush SP, Hegewald KG, Green SM, Cardwell MD, Hayes WK. Effects of a negative pressure venom extraction device (Extractor) on local tissue injury after artificial rattlesnake envenomation in a porcine model. Wilderness Environ Med. 2000 Fall. 11(3):180-8. [Medline].

Bush SP, Green SM, Laack TA, Hayes WK, Cardwell MD, Tanen DA. Pressure immobilization delays mortality and increases intracompartmental pressure after artificial intramuscular rattlesnake envenomation in a porcine model. Ann Emerg Med. 2004 Dec. 44(6):599-604. [Medline].

Bush SP, Cardwell MD. Mojave rattlesnake (Crotalus scutulatus scutulatus) identification. Wilderness Environ Med. 1999 Spring. 10(1):6-9. [Medline].

Gerardo CJ, Quackenbush E, Lewis B, Rose SR, Greene S, Toschlog EA, et al. The Efficacy of Crotalidae Polyvalent Immune Fab (Ovine) Antivenom Versus Placebo Plus Optional Rescue Therapy on Recovery From Copperhead Snake Envenomation: A Randomized, Double-Blind, Placebo-Controlled, Clinical Trial. Ann Emerg Med. 2017 Aug. 70 (2):233-244.e3. [Medline].

Carstairs SD, Kreshak AA, Tanen DA. Crotaline Fab antivenom reverses platelet dysfunction induced by Crotalus scutulatus venom: an in vitro study. Acad Emerg Med. 2013 May. 20(5):522-5. [Medline].

León G, Segura A, Herrera M, Otero R, França FO, Barbaro KC, et al. Human heterophilic antibodies against equine immunoglobulins: assessment of their role in the early adverse reactions to antivenom administration. Trans R Soc Trop Med Hyg. 2008 Nov. 102 (11):1115-9. [Medline].

Sean P Bush, MD, FACEP Professor of Emergency Medicine, The Brody School of Medicine at East Carolina University

Sean P Bush, MD, FACEP is a member of the following medical societies: American College of Emergency Physicians, International Society on Toxicology, Society for Academic Emergency Medicine, Wilderness Medical Society

Disclosure: Nothing to disclose.

John T VanDeVoort, PharmD Regional Director of Pharmacy, Sacred Heart and St Joseph’s Hospitals

John T VanDeVoort, PharmD is a member of the following medical societies: American Society of Health-System Pharmacists

Disclosure: Nothing to disclose.

James Steven Walker, DO, MS Clinical Professor of Surgery, Department of Surgery, University of Oklahoma College of Medicine

James Steven Walker, DO, MS is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Osteopathic Association

Disclosure: Nothing to disclose.

Joe Alcock, MD, MS Associate Professor, Department of Emergency Medicine, University of New Mexico Health Sciences Center

Joe Alcock, MD, MS is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.

Robert L Norris, MD Professor Emeritus, Department of Emergency Medicine, Stanford University Medical Center

Robert L Norris, MD is a member of the following medical societies: American College of Emergency Physicians, Wilderness Medical Society

Disclosure: Nothing to disclose.

Mojave Rattlesnake Envenomation

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