Envenomation by the Mojave rattlesnake (Crotalus scutulatus scutulatus) in southern Arizona, U.S.A

Geographic variation in the clinical features of Mohave rattlesnake (Crotalus scutulatus) envenomations reported to the North American Snakebite Registry

The geographic variation of Mohave rattlesnake (Crotalus scutulatus) venom is well established. We reviewed all the Mohave rattlesnake bites reported to the Toxicology Investigators Consortium's North American Snakebite Registry between January 1, 2015 and 12/31/2021. Data reviewed for this study included details regarding the snake encounter, patient demographics, signs and symptoms, treatment, and outcomes. Our objective was to describe the epidemiology, clinical manifestations, and management of Mohave rattlesnake envenomations using prospective data from two geographically distinct sites. There were 20 subjects, including eight nonpregnant females. Ages ranged from seven to 75 years, median age 48. Nine of the bites were managed in Arizona and 11 in California. In Arizona, all envenomated patients had local swelling. None had neurological toxicity. In California, swelling was present in nine patients. Neurological effects were observed in five subjects. Four Arizona patients and one California patient had hypotension requiring treatment. Each site had one patient with thrombocytopenia. An Arizona patient who sustained a bite to the face was intubated. Rhabdomyolysis occurred in two California patients. All envenomated patients received antivenom. Mohave rattlesnakes have the potential to cause significant local and/or systemic toxicity. Neurotoxicity was not observed in envenomations from Mohave rattlesnakes that presumably lack Mohave toxin, but hypotension and gastrointestinal signs were more common than in bites from snakes believed to possess Mohave toxin. Neurological toxicity was limited to paresthesias and fasciculations. Significant skeletal or respiratory muscle weakness was not observed in our study population.

Neurotoxic respiratory failure absent following Arizona rattlesnake bites

Warnings of neurotoxic respiratory paralysis following envenomation by rattlesnakes (Crotalus sp.) have been included in numerous scholarly publications over the past 60 years, resulting in fear and anxiety in the public and among clinicians. We examine the validity of the widespread belief that rattlesnakes in the arid southwestern United States, and particularly the Mohave Rattlesnake (Crotalus scutulatus), pose a significant risk of medically relevant respiratory weakness and paralysis in humans. A retrospective review of 3440 suspected rattlesnake bites reported to the Arizona Poison and Drug Information Center between 1999 and 2020 produced no evidence of respiratory weakness in a region with three species known to express significant amounts of neurotoxin in their venoms: Crotalus concolor, C. tigris, and the more widely distributed C. scutulatus. A literature review produced numerous warnings regarding respiratory paralysis following envenomation by rattlesnakes in our region that either lacked references or cited sources that did not contain strong supportive data. We found no case reports of neurotoxic respiratory weakness following Arizona rattlesnake bites in the literature and such reports in surrounding states were scant. We conclude that neurotoxic respiratory failure in this region following rattlesnake envenomation is extraordinarily rare. All rattlesnake bites should receive the same consideration and critical care, and warnings about significant risk of respiratory failure are unwarranted, regardless of species involved.

Crotoxin-Induced Mice Lung Impairment: Role of Nicotinic Acetylcholine Receptors and COX-Derived Prostanoids

Respiratory compromise in Crotalus durissus terrificus (C.d.t.) snakebite is an important pathological condition. Considering that crotoxin (CTX), a phospholipase A₂ from C.d.t. venom, is the main component of the venom, the present work investigated the toxin effects on respiratory failure. Lung mechanics, morphology and soluble markers were evaluated from Swiss male mice, and mechanism determined using drugs/inhibitors of eicosanoids biosynthesis pathway and autonomic nervous system. Acute respiratory failure was observed, with an early phase (within 2 h) characterized by enhanced presence of eicosanoids, including prostaglandin E2, that accounted for the increased vascular permeability in the lung. The alterations of early phase were inhibited by indomethacin. The late phase (peaked 12 h) was marked by neutrophil infiltration, presence of pro-inflammatory cytokines/chemokines, and morphological alterations characterized by alveolar septal thickening and bronchoconstriction. In addition, lung mechanical function was impaired, with decreased lung compliance and inspiratory capacity. Hexamethonium, a nicotinic acetylcholine receptor antagonist, hampered late phase damages indicating that CTX-induced lung impairment could be associated with cholinergic transmission. The findings reported herein highlight the impact of CTX on respiratory compromise, and introduce the use of nicotinic blockers and prostanoids biosynthesis inhibitors as possible symptomatic therapy to Crotalus durissus terrificus snakebite.

Phenotypic Variation in Mojave Rattlesnake (Crotalus scutulatus) Venom Is Driven by Four Toxin Families

Phenotypic diversity generated through altered gene expression is a primary mechanism facilitating evolutionary response in natural systems. By linking the phenotype to genotype through transcriptomics, it is possible to determine what changes are occurring at the molecular level. High phenotypic diversity has been documented in rattlesnake venom, which is under strong selection due to its role in prey acquisition and defense. Rattlesnake venom can be characterized by the presence (Type A) or absence (Type B) of a type of neurotoxic phospholipase A2 (PLA2), such as Mojave toxin, that increases venom toxicity. Mojave rattlesnakes (Crotalus scutulatus), represent this diversity as both venom types are found within this species and within a single panmictic population in the Sonoran Desert. We used comparative venom gland transcriptomics of nine specimens of C. scutulatus from this region to test whether expression differences explain diversity within and between venom types. Type A individuals expressed significantly fewer toxins than Type B individuals owing to the diversity of C-type lectins (CTLs) and snake venom metalloproteinases (SVMPs) found in Type B animals. As expected, both subunits of Mojave toxin were exclusively found in Type A individuals but we found high diversity in four additional PLA2s that was not associated with a venom type. Myotoxin a expression and toxin number variation was not associated with venom type, and myotoxin a had the highest range of expression of any toxin class. Our study represents the most comprehensive transcriptomic profile of the venom type dichotomy in rattlesnakes and C. scutulatus. Even intra-specifically, Mojave rattlesnakes showcase the diversity of snake venoms and illustrate that variation within venom types blurs the distinction of the venom dichotomy.

Clinical predictors of tissue necrosis following rattlesnake envenomation

BACKGROUND

Rattlesnake envenomation (RSE) causes edema, hemotoxicity and tissue necrosis. Necrosis may result in permanent disability.

OBJECTIVE

To study patient-related factors associated with tissue necrosis after Crotalus envenomation.

METHODS

Prospective cohort study of patients admitted to the Medical Toxicology service with diagnosis of RSE between April 2011 and November 2014. Inclusion criteria were age ≥18 years and upper extremity (UE) envenomation site. Primary outcome was tissue necrosis, including dermonecrosis, manifesting as bullae. Secondary outcome was amputation.

RESULTS

77 subjects, age 18 to 88 years, met inclusion criteria. Rattlesnake species was unknown in most cases. All received Fab antivenom. 62 (82%) had a digital envenomation. 31 (40.3%) had necrosis. Necrotic area ranged from 0.1 cm² to 14 cm². Procedural interventions, (superficial debridement, dermotomy, surgical exploration, and operative debridement of devitalized tissue) occurred in 25 (32.5%). Five (6.5%) underwent dermotomy and 6 (7.8%) operative debridement. No amputations were performed. Patients with cyanosis on presentation had increased risk of developing necrosis (11/12; RR 2.98 95% CI 1.99-4.46). Ecchymosis on presentation was also associated with increased risk of necrosis (24/32; RR 4.04 95% CI 2.08-7.86). Patients with social or regular ethanol use were more likely to develop necrosis than those without (28/53; RR 4.23 95% CI 1.42-12.6). Regular cocaine use was associated with increased risk of operative debridement (4/6; RR 9.13 95% CI 2.33-35.8). A nonsignificant risk of operative debridement occurred with tobacco use (RR 1.14 95%CI 0.99-1.31 p = 0.09). Time to antivenom did not correlate with risk of necrosis.

CONCLUSION

UE RSE patients who presented with cyanosis, ecchymosis or history of ethanol use were at increased risk of developing necrosis. Cocaine use was associated with increased risk of operative debridement.

Antivenom for Neuromuscular Paralysis Resulting From Snake Envenoming

Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this.

The binding effectiveness of anti-r-disintegrin polyclonal antibodies against disintegrins and PII and PIII metalloproteases: An immunological survey of type A, B and A+B venoms from Mohave rattlesnakes

Snake venoms are known to have different venom compositions and toxicity, but differences can also be found within populations of the same species contributing to the complexity of treatment of envenomated victims. One of the first well-documented intraspecies venom variations comes from the Mohave rattlesnake (Crotalus scutulatus scutulatus). Initially, three types of venoms were described; type A venom is the most toxic as a result of ~45% Mojave toxin in the venom composition, type B lacks the Mojave toxin but contains over 50% of snake venom metalloproteases (SVMPs). Also, type A+B venom contains a combination of Mojave toxin and SVMP. The use of an anti-disintegrin antibody in a simple Enzyme-Linked Immunosorbent Assay (ELISA) can be used to identify the difference between the venoms of the type A, B, and A+B Mohave rattlesnakes. This study implements the use of an anti-recombinant disintegrin polyclonal antibody (ARDPA) for the detection of disintegrins and ADAMs (a disintegrin and metalloproteases) in individual crude snake venoms of Mohave rattlesnakes (Crotalus scutulatus scutulatus) of varying geographical locations. After correlation with Western blots, coagulation activity and LD₅₀ data, it was determined that the antibody allows for a quick and cost-efficient identification of venom types.

Venom variability and envenoming severity outcomes of the Crotalus scutulatus scutulatus (Mojave rattlesnake) from Southern Arizona

Twenty-one Mojave rattlesnakes, Crotalus scutulatus scutulatus (C. s. scutulatus), were collected from Arizona and New Mexico U.S.A. Venom proteome of each specimen was analyzed using reverse-phase HPLC and SDS-PAGE. The toxicity of venoms was analyzed using lethal dose 50 (LD(50)). Health severity outcomes between two Arizona counties U.S.A., Pima and Cochise, were determined by retrospective chart review of the Arizona Poison and Drug Information Center (APDIC) database between the years of 2002 and 2009. Six phenotypes (A-F) were identified based on three venom protein families; Mojave toxin, snake venom metalloproteinases PI and PIII (SVMP), and myotoxin-A. Venom changed geographically from SVMP-rich to Mojave toxin-rich phenotypes as you move from south central to southeastern Arizona. Phenotypes containing myotoxin-A were only found in the transitional zone between the SVMP and Mojave toxin phenotypes. Venom samples containing the largest amounts of SVMP or Mojave toxin had the highest and lowest LD(50s), respectively. There was a significant difference when comparing the presence of neurotoxic effects between Pima and Cochise counties (p=0.001). No significant difference was found when comparing severity (p=0.32), number of antivenom vials administered (p=0.17), days spent in a health care facility (p=0.23) or envenomation per 100,000 population (p=0.06). Although not part of the original data to be collected, death and intubations, were also noted. There is a 10× increased risk of death and a 50× increased risk of intubations if envenomated in Cochise County.

Mojave toxin in venom of Crotalus helleri (Southern Pacific Rattlesnake): molecular and geographic characterization

Mojave toxin (MT) was detected in five of 25 Crotalus helleri (Southern Pacific rattlesnake) sampled using anti-MT antibodies and nucleotide sequence analysis. All of the venoms that were positive for MT were collected from Mt San Jacinto in Riverside Co., California. Since this population is geographically isolated from C. scutulatus scutulatus (Mojave rattlesnake), it is unlikely that this finding is due to recent hybridization. MT concentration differences between C. helleri and C. s. scutulatus reflected the presence of 'isoforms' of the toxin in the venom. Whereas C. s. scutulatus generally has several isoforms of the toxin (detected by Western blotting), only one 'isoform' that focused at pI 5.1 was detected in C. helleri. Both acidic and basic subunits of MT sequences were obtained from C. helleri DNA with primers specific for MT, but only from snakes that had MT in their venom. The sequence identity of the C. helleri acidic subunit to the C. s. scutulatus subunit was 84.9%, whereas the sequence identity of the C. helleri basic subunit was 97% to the C. s. scutulatus basic subunit. Using casein, fibrin, and hide powder azure as substrates, assays for proteolytic activity suggested that C. helleri possesses several different types of metalloproteinases in their venom. However, proteolytic activity was not detected, or present in reduced amounts, in specimens having MT. Clinical neurotoxicity following envenomation by certain populations of C. helleri may be due to MT.

Respiratory compromise in patients with rattlesnake envenomation

Respiratory compromise after rattlesnake envenomation (RSE) is an uncommon yet potentially lethal complication. We were interested in determining the frequency of respiratory compromise in patients treated for RSE. The incidence and indications for intubation were also determined. A retrospective chart review was conducted of all patients treated by medical toxicologists at a tertiary referral hospital between July, 1994 and November, 2000. Out of 294 total patients, 289 charts were reviewed. Of all 289 patients, 214 (74%) received Crotalidae Polyvalent Antivenin (Wyeth-Ayerst) and 23 (8%) had clinical evidence of respiratory compromise. Thirteen of 289 patients (4.4%) were intubated following RSE. No one was intubated for antivenin-induced complications. There were no deaths among studied patients during acute hospitalization. Respiratory compromise following RSE is rare, occurring in only 8% of studied patients. Only 2 patients (0.7%) required intubation as a direct consequence of RSE. No one required intubation for antivenin-induced hypersensitivity reactions.

Neurotoxicity associated with suspected southern Pacific rattlesnake (Crotalus viridis helleri) envenomation

An 18-year-old man was bitten on the hand by a snake he believed to be a Southern Pacific rattlesnake (Crotalus viridis helleri). Within minutes he developed generalized weakness, difficulty breathing, diplopia, dysphagia, and dysphonia. Neurological examination revealed ptosis and decreased motor strength. These symptoms partially improved after administration of Antivenin (Crotalidae) Polyvalent, but the patient continued to have difficulty walking for several days due to weakness. In addition to neurological symptoms, the patient also experienced pain immediately after the bite occurred and rapid swelling of the entire extremity, which extended beyond the shoulder. He complained of a metallic taste in his mouth and developed intense muscle fasciculations of the face, tongue, and upper extremities, which lasted for 2 days and did not improve with antivenin treatment. He exhibited laboratory evidence of coagulopathy and rhabdomyolysis. Although neurotoxins are known to occur in the venom of certain populations of rattlesnakes, only a few clinical reports describing severe neurological symptoms appear in the literature. To our knowledge, this is the first reported case of neurotoxicity associated with a suspected Southern Pacific rattlesnake envenomation.

Comparative characterisation of Russell's viper (Daboia/Vipera russelli) venoms from different regions of the Indian peninsula

Russell's viper (Daboia/Vipera russelli) venom from different regions of India was subjected to chromatographic, electrophoretic, biochemical and immunological analysis. The elution profiles from ion-exchange chromatography and protein banding pattern from SDS-PAGE showed a significant variation in the constituents of venoms. The acidic proteins are found to be predominant in the venoms of eastern and western regions while basic proteins are the major contributors of the northern and southern regional venoms. The major variation of phospholipases A(2) in the venom samples of India may be described as: southern regional venom is rich in basic, toxic PLA(2) while this activity showed a dramatic decrease as one moves towards west, north and eastern regions of India. In addition, the caseinolytic, TAME-hydrolytic, anticoagulant, oedema-inducing and haemorrhagic activities of the venoms have also varied from one region to another. The muscle specimens of mice injected with venoms of different regions showed variable change in the muscle fibre damage and cell morphology. The eastern regional venom is most lethal among all the venoms. The lethal potencies for four regional venoms vary as: eastern>western>southern>northern. The polyclonal antibodies prepared against the venom of southern region showed cross-reaction with the venoms of other regions, but the extent of cross-reaction and diffusion patterns are different. However, the polyclonal antibodies prepared against southern regional venom showed no protection against lethal toxicity of other regional venoms.

Envenomations

Envenomations are uncommon, challenging causes of critical care admissions. This article describes the diagnosis and treatment of envenomations that cause the most critical care admissions in the United States. Most are caused by the following animals: rattlesnakes, copperheads, cottonmouths, coral snakes, brown recluse spiders, and bark scorpions.

Crotalid snake envenomation

Over 5000 Americans suffer from snake bites annually, and of these, nearly one quarter are from poisonous species. Although these cases are undeniably reported, death appears to occur in only a few cases each year, and often reflects delay in obtaining medical care. Two families of venomous snake indigenous to the United States account for most envenomations: Crotalidae (pit vipers or new world vipers) and Elapidae. This article focuses on the snakes of the Crotalidae family.

Mojave rattlesnake envenomation in southern California: a review of suspected cases

To clarify whether Mojave rattlesnake (Crotalus scutulatus scutulatus) envenomations occurring in California cause typical crotalid tissue effects, pain, edema, and ecchymosis, we reviewed charts of snakebite victims at a tertiary care teaching hospital and a moderate-size community hospital. Forty-two patients were bitten within the range of Mojave rattlesnakes. Eight snakes were identified as Mojave rattlesnakes (group 1); of these, four were confirmed by experts in snake identification (group 1a). Fifteen patients were reported bitten by other rattlesnake species (group 2), and in 19 envenomations the species was unknown (group 3). Seventy-five percent of patients in group 1 were reported to have local edema at the envenomation site compared with all of the patients in group 2. Ecchymosis was found in 25% of group 1 patients and 73% of group 2 patients. Pain was documented in only 12% of group 1 and 67% of group 2 victims. Neurotropic events, many severe, were found in 75% of group 1 patients compared with 7% of those in group 2. Although this study does not have the power to justify statistical evaluation, C. scutulatus envenomations do appear inclined to less tissue reaction. A disturbing trend toward severe neurotropic manifestations was also suggested in presumed Mojave rattlesnake envenomations.

Mojave rattlesnake envenomation: prolonged neurotoxicity and rhabdomyolysis

An 11-year-old girl presented to the emergency department with hypoventilation and shock after being bitten by a Mojave rattlesnake. Intubation was required, and she improved rapidly after fluid resuscitation and antivenom administration. She was extubated four hours after envenomation and did well. The patient subsequently developed increased weakness and cranial nerve paresis and required reintubation for respiratory failure at 30 hours after envenomation despite administration of 30 vials of antivenom. She improved after administration of additional antivenom and was extubated ten hours later. Twenty-four hours after envenomation, signs of rhabdomyolysis were noted with myoglobinuria and a creatine phosphokinase level of 96,400 units/L. Myoglobinuric renal failure was treated with mannitol, hydration, and alkalinization of the urine. The patient's renal and neurological functions improved steadily during the following three to four days. Neurotoxic and myotoxic effects of Mojave venom are known to occur but are not well documented in human beings. Recognition of potential complications from envenomation such as respiratory paralysis and rhabdomyolysis with myoglobinuric renal failure is critical.

Snake venom variability: methods of study, results and interpretation

The causes and implications of venom variability are discussed with a review of the literature. Venom variability may have an impact on both primary venom research and management of snakebite, including selection of antivenoms and selection of specimens for antivenom production. Choice of venom is reviewed, including venom collection, maintenance, and pooled venom versus venom milked from individual specimens, the latter being more reliable in many applications. Intraspecific variability resulting in clinical variability of envenomation occurs and is reviewed. Venom variability is considered at several levels; interfamily, intergenus, interspecies, intersubspecies and intraspecies, geographical variation, between individual specimens, and in individual specimens, due to seasonal variation, diet, habitat, age-dependent change, and sexual dimorphism. It is concluded that venom researchers must be aware of venom variability both in selecting their sources of venom and in interpretation of results. Producers of antivenom must utilize an understanding of such variability in selecting sources of venom for antivenom production to ensure representation of all venom types required within each antivenom. Furthermore, clinicians treating snakebite should understand the influence of venom variability on both the presentation of envenomation and the treatment implications.

Fatal rattlesnake envenomation in Arizona: 1969-1984

Case histories of the last nine fatalities (1969-1984), in which the cause of death on the State of Arizona Certificate of Death was snakebite, were reviewed. Six males and three females ranged in age from 2 to 77 years, and were bitten between 0800-2100 hours from April to September. Bites in three adult males were "illegitimate" and of these, two were by captive Mojave rattlesnakes, Crotalus s. scutulatus. The latter two victims had been bitten previously and remained at home, refusing treatment. In the other seven victims, the snakes involved were not identified. However, all localities where bites occurred were within the geographical and altitudinal range for Crotalus atrox and C. s. scutulatus. The apparent cause of death was prolonged hypotension with major organ system failure in five, intestinal hemorrhage in one, and was unknown in three. Major organs were involved as follows: cardiac failure (two); noncardiac pulmonary edema (two); renal failure (two); unconsciousness with airway obstruction and brain damage (two); and coagulopathy with multiple hemorrhage sites (one). Seven of the nine deaths appeared to be preventable. Four delayed going to a medical facility and six did not have hypotension corrected. Antivenin was not administered early (first four hours) or in adequate amounts (10 vials or more) because of delayed arrival in five or physician's decision in four. Pre-existing cardiac disease contributed to death of two victims. Rattlesnake bite victims should not delay travel to a medical facility and hypotension must be treated aggressively and appropriately.

The distribution among ophidian venoms of a toxin isolated from the venom of the Mojave rattlesnake (Crotalus scutulatus scutulatus)

A toxin analogous to Mojave toxin or protein K' was isolated from venom of the Mojave rattlesnake (Crotalus s. scutulatus) by anion exchange and gel permeation chromatography. This toxin has an apparent native molecular weight of 20,000-22,000, a subunit molecular weight of 14,000 and a pI of 4.9-5.0. The i.p. LD50 is 0.094 mg/kg for mice. A wide variety of ophidian venoms (crotaline, viperine, elapid, hydrophid and colubrid) were examined for the presence of this toxin using Ouchterlony, immunoelectrophoresis, ELISA and Western transfer. High concentrations were found in 4 of 6 C. scutulatus venom samples, 2 of 3 C. durissus samples and samples from C. viridis concolor and C. tigris. A moderate concentration was found in 1 of 3 C. durissus samples and low to trace concentrations in 1 C. durissus sample, 1 C. scutulatus sample, 2 of 12 C. atrox samples and a Trimeresurus flavoviridis sample, the latter being the only instance of detection of the toxin in a snake other than a rattlesnake. The toxin appears in at least two phylogenetic lines of rattlesnakes, and its geographic distribution in North American rattlesnake species resembles a mosaic.

Reptile envenomations

Venomous reptiles are distributed in select habitats in temperate and tropical areas of the world with few geographical exceptions, and have adapted to not only terrestial existence, but to arboreal and aquatic environments as well. Venomous snakes are found in the families Colubridae (fixed and rear fanged snakes), Elapidae (fixed and front fang snakes), Hydrophiidae (sea snakes), Viperidae (Old World vipers) and Crotalidae (pit vipers). Venomous lizards are found in the United States and Mexico, and comprise the family Helodermatidae. Venom delivery systems and venom components show diversity, and greater appreciation of interspecies clinical effect is apparent in modern literature. First aid care for the bitten individual remains controversial, but most authorities now tend to minimize field procedures, especially those endeavors which may potentially damage tissue. The weight of evidence in the area of definitive therapy lies with the use of antivenin, although proponents of primary surgical intervention in crotalid envenomations have followings, particularly in the United States. Recent developments in "purification" of existing antivenins are promising, and attention to species-specific antivenin production, especially to the venoms of the crotalid species of the New World, is encouraged. Due to a growing international traffic in venomous animals for the purposes of research and supply of zoos and private reptile collections, knowledge of resources for assistance in bites of non-indigenous reptiles is a growing consideration.

Geographical variation in Crotalus scutulatus scutulatus (Mojave rattlesnake) venom properties

Individual venom samples were analyzed from 12 specimens of Crotalus scutulatus scutulatus, from north of Tucson to the extreme southeastern region of Arizona. Six of the specimens, from north of Tucson, produced venom lethal toxicity (i.p. LD50) values in mice of 2.0-6.0 mg/kg. These coincided with the values previously reported for C. s. scutulatus in the Phoenix, Arizona, region and designated as type B venom (Glenn and Straight, 1978). In contrast, the venom LD50 of six individuals from extreme southeastern Arizona, including one individual near Tucson, ranged from 0.22-0.46 mg/kg. This corresponds to the values for C. s. scutulatus venom previously reported and designated as type A venom (Glenn and Straight, 1978). Specimens with type A venom have been collected in California, Nevada, Utah and regions of Arizona. In addition to differences in lethal toxicity, the type B venom consistently exhibits a different protein profile, greater proteolytic activity, greater hemorrhagic activity and contains little or none of the major lethal toxin, Mojave toxin, compared to the type A venom. No external morphological characteristic could be found differentiating the type A venom specimens from the type B venom specimens. These findings further confirm the geographical variation of C. s. scutulatus venom in Arizona.