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Lizard Envenomation

  • Author: Robert L Norris, MD; Chief Editor: Joe Alcock, MD, MS  more...
 
Updated: Oct 27, 2015
 

Background

There are 2 extant species of lizards known to be venomous, the Gila monster (Heloderma suspectum, with 2 subspecies) and the Mexican beaded lizard (Heloderma horridum, with 4 subspecies). 

There is ongoing debate regarding possible venom production by some other lizard species such as the Komodo dragon (Varanus komodoensis), but there is no current evidence to support human envenomations by any other lizards,[1] and these will not be further discussed in this article.

A Gila monster (Heloderma suspectum). Photo by Mic A Gila monster (Heloderma suspectum). Photo by Michael Cardwell.

The Gila monster is found in the desert regions of Arizona, western New Mexico, southeastern California,[2] the southern tip of Nevada, extreme southwestern Utah, and northwestern Mexico. The beaded lizard is found only in Mexico and Guatemala, south of the range of the Gila monster.

Both lizards have heavy bodies with large heads and powerful jaws. The beaded lizard is larger than the Gila monster, reaching almost a meter in length, whereas the Gila monster's maximal size is approximately 0.5 m.

Close-up of the head of a Gila monster. Clearly ev Close-up of the head of a Gila monster. Clearly evident is the bulging musculature of the jaws, which gives this animal a tenacious bite. Photo by Holly McNally.
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Pathophysiology

The venom apparatus is much less sophisticated than that of most venomous snakes. A pair of multilobed labial venom glands (modified submandibular glands) lie in the anterior portion of the lower jaw. Venom is conducted from each lobe through a single duct (H horridum) or a series of ducts (H suspectum) and is deposited into a labial mucosal pocket adjacent to the anterior teeth.[3]

The teeth (approximately 20 per jaw) are grooved and loosely attached to the jaws. Venom is conducted via capillary action along these grooves into the victim's tissues as the lizard bites and chews. The more irritated the lizard is when it bites, the more it salivates and the greater the venom yield. Effective envenomation in humans probably occurs in less than 70% of bites.

The dentition of a Gila monster. The grooved surfa The dentition of a Gila monster. The grooved surfaces of the teeth are evident. These grooves allow for venom movement from the venom glands into the victim's tissues. Photo by Michael Cardwell.

The venoms of these 2 lizards are remarkably similar and contain a number of components, including L-amino acid oxidase, hyaluronidase, phospholipase A, serotonin, and highly active kallikreins that release vasoactive kinins. The venom contains no neurotoxins or any enzymes that significantly affect coagulation. In laboratory animals, the venom is as potent as some rattlesnake venoms. Rare hypersensitivity to helodermatid venom has been reported.[4, 5]

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Epidemiology

Frequency

United States

Bites are very infrequent and usually involve captive specimens. A significant number of bites probably go unreported because private keepers of these protected lizards may be reluctant to seek medical attention.

International

No data regarding current incidence of bites by venomous lizards in Mexico are available.

Race

No data are available to support any racial predilection to lizard bites.

Sex

Young males are more likely to intentionally interact with venomous wildlife, and are, therefore at greater risk for bites.

Age

While there are no large studies reporting the age distribution of venomous lizard bites, it is likely that those at greatest risk will be children, adolescents, and young adults. Young children may be at increased risk of bites if they come across a wild Heloderma specimen, as they may not comprehend the risk. Adolescents and young adults may be more prone to intentionally interact with or collect such lizards, despite knowing their venomous nature.

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Contributor Information and Disclosures
Author

Robert L Norris, MD Professor, 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, Society for Academic Emergency Medicine, International Society of Toxinology, American Medical Association, California Medical Association, Wilderness Medical Society

Disclosure: Nothing to disclose.

Specialty Editor Board

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.

A Antoine Kazzi, MD Deputy Chief of Staff, American University of Beirut Medical Center; Associate Professor, Department of Emergency Medicine, American University of Beirut, Lebanon

A Antoine Kazzi, MD is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

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.

Additional Contributors

Mark S Slabinski, MD, FACEP, FAAEM Vice President, EMP Medical Group

Mark S Slabinski, MD, FACEP, FAAEM is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, Ohio State Medical Association

Disclosure: Nothing to disclose.

References
  1. Fry BG, Wroe S, Teeuwisse W, et al. A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus. Proc Natl Acad Sci U S A. 2009 Jun 2. 106 (22):8969-74. [Medline].

  2. Beck DD. Biology of Gila Monsters and Beaded Lizards. Berkeley, CA: University of California Press; 2005. 1-211.

  3. Strimple PD, Tomassoni AJ, Otten EJ. Report on envenomation by a Gila monster (Heloderma suspectum) with a discussion of venom apparatus, clinical findings, and treatment. Wilderness Environ Med. 1997 May. 8(2):111-6. [Medline].

  4. Mebs D. Clinical toxicology of Helodermatidae lizard bites. In: Handbook of Clinical Toxicology of Animal Venoms and Poisons. 1995: 361-366.

  5. Piacentine J, Curry SC, Ryan PJ. Life-threatening anaphylaxis following gila monster bite. Ann Emer Med. 1986. 15:959-961. [Medline].

  6. French RN, Ash J, Brooks DE. Gila monster bite. Clin Toxicol (Phila). 2012 Feb. 50(2):151-2. [Medline].

  7. Bou-Abboud CF, Kardassakis DG. Acute myocardial infarction following a Gila monster (Heloderma suspectum cinctum) bite. West J Med. 1988. 148(5):577-579. [Medline].

  8. Preston CA. Hypotension, myocardial infarction, and coagulopathy following gila monster bite. J Emerg Med. 1989 Jan-Feb. 7 (1):37-40. [Medline].

  9. French R, Brooks D, Ruha AM, Shirazi F, Chase P, Boesen K, et al. Gila monster (Heloderma suspectum) envenomation: Descriptive analysis of calls to United States Poison Centers with focus on Arizona cases. Clin Toxicol (Phila). 2015 Jan. 53 (1):60-70. [Medline].

  10. Brown DE, Carmony NB. Gila Monster: Facts and Folklore of America's Aztec Lizard. 1991. 1-126.

 
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A Gila monster (Heloderma suspectum). Photo by Holly McNally.
Close-up of the head of a Gila monster. Clearly evident is the bulging musculature of the jaws, which gives this animal a tenacious bite. Photo by Holly McNally.
The dentition of a Gila monster. The grooved surfaces of the teeth are evident. These grooves allow for venom movement from the venom glands into the victim's tissues. Photo by Michael Cardwell.
A Gila monster (Heloderma suspectum). Photo by Michael Cardwell.
 
 
 
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