Gila monster envenomation

Crouching Zookeeper, Hidden Dragon: A Case of a Komodo Dragon Bite

BACKGROUND

The Komodo dragon (Varanus komodoensis) is the world's largest living lizard and exists in private captivity worldwide. Bites to humans are rare and have been proposed to be both infectious and venomous.

CASE REPORT

A 43-year-old zookeeper was bitten on the leg by a Komodo dragon and suffered local tissue damage with no excessive bleeding or systemic symptoms to suggest envenomation. No specific therapy was administered other than local wound irrigation. The patient was placed on prophylactic antibiotics and on follow-up, which revealed no local or systemic infections, and no other systemic complaints. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Although venomous lizard bites are uncommon, prompt recognition of possible envenomation and management of these bites is important. Komodo dragon bites may produce not only superficial lacerations but also deep tissue injury, but are unlikely to produce serious systemic effects; whereas Gila monster and beaded lizard bites may cause delayed angioedema, hypotension, and other systemic symptoms. Treatment in all cases is supportive.

The Dragon's Paralysing Spell: Evidence of Sodium and Calcium Ion Channel Binding Neurotoxins in Helodermatid and Varanid Lizard Venoms

Bites from helodermatid lizards can cause pain, paresthesia, paralysis, and tachycardia, as well as other symptoms consistent with neurotoxicity. Furthermore, in vitro studies have shown that Heloderma horridum venom inhibits ion flux and blocks the electrical stimulation of skeletal muscles. Helodermatids have long been considered the only venomous lizards, but a large body of robust evidence has demonstrated venom to be a basal trait of Anguimorpha. This clade includes varanid lizards, whose bites have been reported to cause anticoagulation, pain, and occasionally paralysis and tachycardia. Despite the evolutionary novelty of these lizard venoms, their neuromuscular targets have yet to be identified, even for the iconic helodermatid lizards. Therefore, to fill this knowledge gap, the venoms of three Heloderma species (H. exasperatum, H. horridum and H. suspectum) and two Varanus species (V. salvadorii and V. varius) were investigated using Gallus gallus chick biventer cervicis nerve–muscle preparations and biolayer interferometry assays for binding to mammalian ion channels. Incubation with Heloderma venoms caused the reduction in nerve-mediated muscle twitches post initial response of avian skeletal muscle tissue preparation assays suggesting voltage-gated sodium (Na_V) channel binding. Congruent with the flaccid paralysis inducing blockage of electrical stimulation in the skeletal muscle preparations, the biolayer interferometry tests with Heloderma suspectum venom revealed binding to the S3–S4 loop within voltage-sensing domain IV of the skeletal muscle channel subtype, Na_V1.4. Consistent with tachycardia reported in clinical cases, the venom also bound to voltage-sensing domain IV of the cardiac smooth muscle calcium channel, Ca_V1.2. While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both Na_V1.4 and Ca_V1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.

Severe Heloderma spp. envenomation: a review of the literature

Context: Heloderma bites are rare and generally mild, but a few cases can be life threatening. Methods: Description of Heloderma bite was searched in medical literature. Discussion: We present a synthesis of clinical and biomedical effects of envenomation by Heloderma sp. based on 22 well identified cases described in medical literature. Three life-threatening syndromes, concomitant or not, may be involved: (a) angioedema which can lead to respiratory tract obstruction, (b) significant fluid losses due to diarrhea, vomiting and sweating, associated with hypokalemia and sometimes metabolic acidosis, and (c) atrioventricular conduction disorders simulating cardiac ischemia. Conclusion: Heloderma bite are quite rare and generally mild. However, few severe cases may require emergency resuscitation. There is no antivenom, and the treatment is only symptomatic and supportive.

Report of a severe Heloderma suspectum envenomation

BACKGROUND

Heloderma bites are rare and generally mild, but a few cases can be life threatening.

CASE REPORT

We report a case of Heloderma suspectum envenomation in a healthy 39-year-old herpetologist. The patient rapidly developed tongue and lip swelling associated with stridor. On arrival at ICU, he was hypotensive, and in shock with atrial fibrillation requiring electrical cardioversion. Blood tests showed hypokalemia (2 mmol·L^-1), associated with moderate low blood electrolytes which were corrected rapidly. In addition, he presented hematological abnormalities (INR = 1.34 and fibrinogen levels at 80 mg·dL^-1) without active bleeding. All clinical and biological signs normalized without specific intervention and was discharged 4 days post-bite. The patient discharged 3 days after hospital presentation and fully recovered in 2 months.

DISCUSSION/CONCLUSION

The case presented here showed the three severe complications described after Heloderma bite: a) angioedema, b) fluid loss associated with hypokalemia and metabolic acidosis, and c) cardiac disorders simulating ischemia.

A case of Gila monster (Heloderma suspectum) bite

Introduction:

A variety of exotic reptiles are kept as “pets” and the ownership of these animals is rising in Hong Kong. Two lizard species are known to be venomous: the Gila monster ( Heloderma suspectum) and the Mexican Beaded Lizard (Heloderma horridum). Both of them are native to the North America but are traded in the pet markets. Bites from these lizards are capable of causing severe envenomation in humans.

Case presentation:

A 41-year-old man presented to the emergency department after bitten by his exotic pet. His right hand was bitten by a Gila monster resulting in local swelling and intense pain. The local envenomation lasted for about 12 hours and then gradually improved.

Discussion:

Bite by Gila monster could result in local and systemic envenomation. Local envenomation includes intense pain of the injured site, edema and paraesthesia. Systemic envenomation including hypotension and airway edema occurs in severe envenomation.

Conclusion:

With the increasing popularity of keeping exotic pets in Hong Kong, envenomation by exotic venomous animals may be encountered by the emergency physicians. Knowledge about the potential envenomation effects of these exotic animals is essential for proper management of the patients.

Fossilized venom: the unusually conserved venom profiles of Heloderma species (beaded lizards and gila monsters)

Research into snake venoms has revealed extensive variation at all taxonomic levels. Lizard venoms, however, have received scant research attention in general, and no studies of intraclade variation in lizard venom composition have been attempted to date. Despite their iconic status and proven usefulness in drug design and discovery, highly venomous helodermatid lizards (gila monsters and beaded lizards) have remained neglected by toxinological research. Proteomic comparisons of venoms of three helodermatid lizards in this study has unravelled an unusual similarity in venom-composition, despite the long evolutionary time (~30 million years) separating H. suspectum from the other two species included in this study (H. exasperatum and H. horridum). Moreover, several genes encoding the major helodermatid toxins appeared to be extremely well-conserved under the influence of negative selection (but with these results regarded as preliminary due to the scarcity of available sequences). While the feeding ecologies of all species of helodermatid lizard are broadly similar, there are significant morphological differences between species, which impact upon relative niche occupation.

The structural and functional diversification of the Toxicofera reptile venom system

The evolutionary origin and diversification of the reptilian venom system is described. The resolution of higher-order molecular phylogenetics has clearly established that a venom system is ancestral to snakes. The diversification of the venom system within lizards is discussed, as is the role of venom delivery in the behavioural ecology of these taxa (particularly Varanus komodoensis). The more extensive diversification of the venom system in snakes is summarised, including its loss in some clades. Finally, we discuss the contentious issue of a definition for "venom", supporting an evolutionary definition that recognises the homology of both the venom delivery systems and the toxins themselves.

Functional and structural diversification of the Anguimorpha lizard venom system

Venom has only been recently discovered to be a basal trait of the Anguimorpha lizards. Consequently, very little is known about the timings of toxin recruitment events, venom protein molecular evolution, or even the relative physical diversifications of the venom system itself. A multidisciplinary approach was used to examine the evolution across the full taxonomical range of this ∼130 million-year-old clade. Analysis of cDNA libraries revealed complex venom transcriptomes. Most notably, three new cardioactive peptide toxin types were discovered (celestoxin, cholecystokinin, and YY peptides). The latter two represent additional examples of convergent use of genes in toxic arsenals, both having previously been documented as components of frog skin defensive chemical secretions. Two other novel venom gland-overexpressed modified versions of other protein frameworks were also recovered from the libraries (epididymal secretory protein and ribonuclease). Lectin, hyaluronidase, and veficolin toxin types were sequenced for the first time from lizard venoms and shown to be homologous to the snake venom forms. In contrast, phylogenetic analyses demonstrated that the lizard natriuretic peptide toxins were recruited independently of the form in snake venoms. The de novo evolution of helokinestatin peptide toxin encoding domains within the lizard venom natriuretic gene was revealed to be exclusive to the helodermatid/anguid subclade. New isoforms were sequenced for cysteine-rich secretory protein, kallikrein, and phospholipase A(2) toxins. Venom gland morphological analysis revealed extensive evolutionary tinkering. Anguid glands are characterized by thin capsules and mixed glands, serous at the bottom of the lobule and mucous toward the apex. Twice, independently this arrangement was segregated into specialized serous protein-secreting glands with thick capsules with the mucous lobules now distinct (Heloderma and the Lanthanotus/Varanus clade). The results obtained highlight the importance of utilizing evolution-based search strategies for biodiscovery and emphasize the largely untapped drug design and development potential of lizard venoms.

Lizard bites of the head and neck

BACKGROUND

As the ownership of lizards becomes more prevalent in the United States, injuries from these exotic pets will increase. Emergency and primary care physicians must be familiar with the proper management of lizard bites to the head and neck.

OBJECTIVES

The aim of this case report is to discuss the potential complications and proper management of lizard bites to the head and neck.

CASE REPORT

A 47-year-old man presented to the emergency department 3 h after his 5-foot iguana bit his face. The wounds were irrigated and primarily closed. Tetanus prophylaxis was administered. He was given oral amoxicillin/clavulanate potassium for 7 days. Sutures were removed 1 week after the repair.

CONCLUSIONS

Topical antiseptic care, verification of tetanus status, primary wound closure, and careful monitoring of non-venomous lizard bites is recommended for lizard bites to the head and neck. Wounds at risk for infection should be treated with a quinolone or other antibiotics covering Salmonella as well as human skin flora. Venomous lizard (e.g., Gila monster and Mexican Beaded Lizard) bites require prompt attention due to potentially significant morbidities including anaphylaxis, disseminated intravascular coagulation, and acute myocardial infarction.

Novel venom proteins produced by differential domain-expression strategies in beaded lizards and gila monsters (genus Heloderma)

The origin and evolution of venom proteins in helodermatid lizards were investigated by multidisciplinary techniques. Our analyses elucidated novel toxin types resultant from three unique domain-expression processes: 1) The first full-length sequences of lethal toxin isoforms (helofensins) revealed this toxin type to be constructed by an ancestral monodomain, monoproduct gene (beta-defensin) that underwent three tandem domain duplications to encode a tetradomain, monoproduct with a possible novel protein fold; 2) an ancestral monodomain gene (encoding a natriuretic peptide) was medially extended to become a pentadomain, pentaproduct through the additional encoding of four tandemly repeated proline-rich peptides (helokinestatins), with the five discrete peptides liberated from each other by posttranslational proteolysis; and 3) an ancestral multidomain, multiproduct gene belonging to the vasoactive intestinal peptide (VIP)/glucagon family being mutated to encode for a monodomain, monoproduct (exendins) followed by duplication and diversification into two variant classes (exendins 1 and 2 and exendins 3 and 4). Bioactivity characterization of exendin and helokinestatin elucidated variable cardioactivity between isoforms within each class. These results highlight the importance of utilizing evolutionary-based search strategies for biodiscovery and the virtually unexplored potential of lizard venoms in drug design and discovery.

["NPAs": a new allergic risk?]

In recent years, to the list of classic pet animals (dogs and cats) as allergens we must now add the "new pet animals" (NPAs). This group of animals, referred to by the Anglo-Saxons as "pets", includes both those previously recognized (rabbit, guinea pig, hamster, birds) and the "truly new NPAs"; by general agreement "NPA" will include all animals other than cats and dogs. Some rather rare animals are regularly added to this list. The emergence of "NPAs" can be related to a social phenomenon, in particular, to the fashion and need for the exotic (http://www.aquadesign.be). They are a very diverse group: warm-blooded animals, spiders, batrachia (frogs, toads, salamanders, etc.) and reptiles. Besides the physical risks from their natural aggressive behaviour, the "NPAs" can be an allergic risk factor and this risk has a tendency to increase. Allergists and paediatricians have a role to play in the diagnosis and prevention of these allergies by giving advice on the choice of pet animals. This review concerns allergies to rodents, reptiles, batrachians, spiders, etc.

Envenomation by a wild Guatemalan Beaded Lizard Heloderma horridum charlesbogerti

BACKGROUND

The Guatemalan Beaded Lizard (Heloderma horridum charlesbogerti) is an endemic venomous lizard that inhabits southeastern Guatemala. Published reports of bites by Beaded Lizard are scarce. This is the first case report of a bite from Heloderma horridum charlesbogerti.

CASE REPORT

A 24-year-old man was bitten on the left hand by a juvenile Heloderma horridum charlesbogerti. The lizard remained attached for approximately 15 seconds. The patient experienced severe local pain, dizziness, diaphoresis, vomiting, severe paresthesia in his left hand and arm, and hypotension (70/52 mm/Hg). He was treated with intravenous ketorolac, chlorpheniramine, methylprednisolone, antibiotics, ondansentron, and normal saline. Hematology tests revealed leukocytosis (12,600/mm3). Symptoms improved and the patient was discharged from hospital 24 hours after admission.

CONCLUSION

The case reported here shows that bites by Heloderma produce severe clinical effects shortly after the bite. Management consists of waiting for the lizard to relax its bite pressure and using pliers to open lizard's mouth and pull out the bitten extremity, a careful manual search for teeth remnants, and supportive care. In our case, severe pain, unresponsive to non-steroidal anti-inflammatory analgesics, was a major problem. Parethesias resolve quickly but pain may persist for up to 12 hours after the bite. A full recovery is expected.

Nucleoside composition of Heloderma venoms

Venoms of Heloderma horridum and Heloderma suspectum were analyzed for the possible presence of purine and pyrimidine nucleosides. Adenosine, cytidine, guanosine, hypoxanthine, inosine, and uridine were found in mug quantities. These amounts are much smaller than those seen in many elapid or viperine venoms, but greater and more varied than those found in crotaline venoms. While their contribution to the hypotension induced by Heloderma venoms may be minor, venom nucleosides nonetheless act in concert with kallikreins/hemorrhagins, alkaline phosphomonoesterase, 5'-nucleotidase, helodermin, helospectins, helothermine, and serotonin. The use of nucleosides as toxins is therefore a generalized squamate strategy, rather than the exclusive province of snakes. Both Heloderma venoms were found to be devoid of NADase and phosphodiesterase activities. Enzymes to release endogenous purines in the prey, are not significant components of Heloderma venoms.

Envenomation by the Mexican beaded lizard: a case report

BACKGROUND

Envenomations by venomous lizards are rare. A single report of envenomation by a Mexican beaded lizard (Heloderma horridum) has been published. Further, anaphylaxis secondary to lizard envenomation has only been reported with the Gila monster. We report an envenomation that resulted in both systemic toxicity and anaphylaxis.

CASE REPORT

A 40-year-old male was bitten on his hand by a captive Mexican beaded lizard. The patient experienced severe local pain, dizziness, vomiting, and diaphoresis. Upon arrival to the hospital, he was lethargic, vomiting, and in severe pain with marked swelling of his hand, lips, and tongue. His blood pressure was 110/63 mm/Hg with a pulse of 60 beats/minute. The patient's oxygen saturation decreased to 55%, and he required oxygen, although cyanosis was not observed. He was treated with normal saline, diphenhydramine, methylprednisolone, famotidine, ondansetron, morphine, and hydromorphone. The patient was admitted to intensive care where he continued to complain of severe pain requiring morphine. Local X-ray revealed only soft tissue swelling. Remarkable initial laboratory values included WBC 18,500 k/mm3 with 80% segs. Over the next eight hours, the patient's symptoms gradually improved. He had persistent local swelling at the bite site along with erythematous streaking up the forearm. He had an uneventful hospital course until his eventual discharge the following day.

CONCLUSION

Significant envenomations by members of the Helodermatidae family are rare. Systemic toxicity usually resolves within one to two days with supportive care. Prior envenomations may predispose patients to anaphylactic reactions.

Report on envenomation by a Gila monster (Heloderma suspectum) with a discussion of venom apparatus, clinical findings, and treatment

Human envenomations by Heloderma species are a rare but clinically important medical problem. We report a case of an adult male bitten on the left hand by a 50-cm male, captive specimen of Heloderma suspectum (Gila monster). Immediate signs and symptoms included pain at the bite site radiating into the arm and axilla and swelling of the hand and forearm. Systemic complaints of nausea, diaphoresis, and dizziness (without a decrease in blood pressure) lasted approximately 1 hour, and laboratory studies were normal. The patient's course was uneventful except for persistent hyperesthesia, which eventually abated. Two types of helodermatid bites produce distinct clinical pictures. The chewing bite potentially causes more envenomation than the slashing bite. The venom contains a number of protein and nonprotein components including serotonin, a bradykinin-releasing substance, protease, hyaluronidase, helodermin, and gilatoxin. The clinical presentation of a helodermatid bite can include pain, edema, hypotension, nausea, vomiting, weakness, and diaphoresis. No antivenin is commercially available. Treatment is supportive, and although first aid measures such as suction or compression may impede venom movement, they are unproved. Cryotherapy, tourniquet, and excision are dangerous and should not be used.