Introduction
Background
Two species of venomous lizards exist, the Gila monster (Heloderma suspectum, with 2 subspecies) and the Mexican beaded lizard (Heloderma horridum, with 3 subspecies).
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, the southern tip of Nevada, extreme southwestern Utah, and northwestern Mexico. The beaded lizard is found only in Mexico, south of the location 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 evident is the bulging musculature of the jaws, which gives this animal a tenacious bite. Photo by Holly McNally.
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 duct and is deposited into a labial mucosal pocket adjacent to the anterior teeth.
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 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.1,2
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.
Mortality/Morbidity
- No documented deaths caused solely by a Gila monster bite have occurred in the United States.
- It is believed that a prolonged bite received by a small individual, such as an infant or toddler, could result in death.
- Severe pain following a helodermatid bite may last many hours and generalized weakness can persist for several days.
- Described rare complications include shock, myocardial infarction, allergic/anaphylactic reaction, and coagulopathy.3,2,4
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.
Clinical
History
- The vast majority of individuals who are bitten by Gila monsters or beaded lizards are intentionally interacting with the animals, and the history of the bite usually is clear.
- To help estimate the severity of envenomation, it is important to estimate the length of time the lizard remained attached to the victim. While an effective envenomation can occur with a contact time of a few seconds, if the lizard manages to hang on for a period of minutes, the bite could be very serious, potentially lethal.
- The victim may present with many signs and symptoms, including the following:
- Multiple lacerations that may bleed profusely
- Severe throbbing or burning pain at the bite site that may radiate proximally
- Discoloration at the bite site (eg, cyanosis, ecchymosis)
- Generalized weakness
- Nausea and vomiting
- Shortness of breath
- Sweating
- Numbness
- Dizziness
- Faintness
- Progressive edema
- Painful lymph nodes
- Angioedema
Physical
Vital signs should be assessed and closely monitored.
- Local signs
- Multiple bleeding lacerations
- Edema
- Cyanosis or ecchymosis
- Vasospasm
- Retained teeth (Closely examine wounds and probe for foreign bodies.)
- Necrosis (rare)
- Systemic signs
- Tachycardia
- Hypotension
- Respiratory distress
- Diaphoresis
- Lymphangitis and lymphadenopathy
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| References |
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References
Mebs D. Clinical toxicology of Helodermatidae lizard bites. In: Handbook of Clinical Toxicology of Animal Venoms and Poisons. 1995: 361-366.
Piacentine J, Curry SC, Ryan PJ. Life-threatening anaphylaxis following gila monster bite. Ann Emer Med. 1986;15:959-961. [Medline].
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].
Preston CA. Hypotension, myocardial infarction, an coagulopathy following gila monster bite. J Emer Med. 1989;7:37-40. [Medline].
Brown DE, Carmony NB. Gila Monster: Facts and Folklore of America's Aztec Lizard. 1991;1-126.
Cantrell FL. Envenomation by the Mexican beaded lizard: a case report. J Toxicol Clin Toxicol. 2003;41(3):241-4. [Medline].
Hooker KR, Caravati EM. Gila monster envenomation. Ann Emerg Med. 1994;24(4):731-735. [Medline].
Kunkel DB. Bites of venomous reptiles. Emerg Med Clin North Am. Aug 1984;2(3):563-77. [Medline].
Kunkel DB, Curry SC, Vance MV, Ryan PJ. Reptile envenomations. J Toxicol Clin Toxicol. 1983-84;21(4-5):503-26. [Medline].
Miller MF. Gila monster envenomation. Ann Emerg Med. May 1995;25(5):720. [Medline].
Russell FE. Snake Venom Poisoning. Scholium International, Inc;1983:1-562.
Stahnke HL, Heffron WA, Lewis DL. Bite of the Gila monster. Rocky Mt Med J. Sep 1970;67(9):25-30. [Medline].
Streiffer RH. Bite of the venomous lizard, the Gila monster. Postgrad Med. Feb 1 1986;79(2):297-9, 302. [Medline].
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. May 1997;8(2):111-6. [Medline].
Further Reading
Keywords
lizard bite, lizard envenomations, venomous lizards, Gila monster, treatment, symptoms, Heloderma suspectum, Mexican beaded lizard, Heloderma horridum
