Mohave Rattlesnake (Crotalus scutulatus) Identification Revisited.

Crotalus scutulatus (Mohave rattlesnake) is a clinically significant pit viper broadly distributed across much of the arid southwestern United States and mainland Mexico. Identification of C scutulatus is a concern among emergency medical service and emergency department personnel owing to its reputation for severe envenomations and difficulty in visually differentiating between C scutulatus and other species, primarily Crotalus atrox (western diamond-backed rattlesnake). We contrast distinctive characteristics of C scutulatus, C atrox, and 3 other sympatric species: Crotalus molossus, Crotalus ornatus, and Crotalus viridis (western and eastern black-tailed rattlesnakes and prairie rattlesnake, respectively). Greenish coloration eliminates C atrox but does not confirm C scutulatus. Obvious coarse and fine speckling of the dorsal pattern and a pale postocular stripe intersecting the mouth characterize C atrox. Dorsal speckling is insignificant or absent in the other species, whereas the pale postocular stripe passes above the mouth in C scutulatus and C viridis and is absent in C molossus and C ornatus. Tails boldly ringed with alternating black and white or contrasting shades of gray are shared by C atrox and C scutulatus, respectively, but a lack of boldly ringed tails characterizes the other species. The proximal rattle segment is yellow and black, or entirely yellow, in C scutulatus but black in the others. The most reliable visual identifications are based on evaluations of multiple traits, all of which are variable to some extent. Traits such as tail ring width and the size and number of crown scales have frequently been overemphasized in the past.

Snake eyes: Characterization of topical ocular exposures from rattlesnakes in Arizona.

Patients occasionally present with reports of ocular exposure to fluids from rattlesnakes, claiming or suspecting the substance to be venom. This study set out to evaluate and characterize reported cases of suspected venom-induced ophthalmia in humans. A retrospective review of rattlesnake exposures reported to the Arizona Poison and Drug Information Center over a 24-year period was conducted for ocular exposures. Recorded information included patient demographics, clinical course, laboratory results, and treatments. Documentation regarding interactions between patients and snakes was reviewed by Arizona Poison and Drug Information Center herpetologists to evaluate what substance was expelled from the snake resulting in ocular exposure. Our review of rattlesnake encounters found a total of 26 ocular exposure cases. Patient demographics were largely intentional interactions and involved the male sex. Symptoms ranged from asymptomatic to minor effects with 46.2% managed from home and treated with fluid irrigation. A review of cases by herpetologists concluded the exposure patients commonly experienced was to snake musk. Kinematics of venom expulsion by rattlesnakes conclude the venom gland must be compressed, fangs erected to ≥60o, and fang sheath compressed against the roof of the mouth for venom expulsion. Evidence suggests the chance of venom "spitting" by rattlesnakes is close to zero. Rattlesnakes are documented to forcefully expel airborne malodorous "musk" defensively. An important distinction to remember is musk has a foul odor and is usually colorless, while venom is comparatively odorless and yellow. Rattlesnake venom-induced ophthalmia is a rare event as venom expulsion requires the kinematics of feeding or defensive bites. If the rattlesnake is not in the process of biting or otherwise contacting some other object with its mouth, it is more biologically plausible patients are being exposed to snake musk as a deterrent. Whether it's venom or musk, topical exposure to the eyes should prompt immediate irrigation.

Fashionably late: A characterization of late coagulopathies in rattlesnake envenomations between Fab and F(ab')2 antivenoms.

BACKGROUND: Rattlesnake envenomation may lead to a multitude of clinical effects, including a late onset hemorrhage. Laboratory values such as platelets and fibrinogen are commonly used to assess the risk of developing a life-threatening bleed. To date, no specific threshold has been identified that links a lab value to the risk of bleeding. This has led to widespread practice variability among clinicians managing snake bites. In assessing risk for patients, we apply the concept that the more abnormal the lab values are, the higher the risk probably is. Late onset coagulopathies pose a unique clinical challenge because they indicate the potential risk for a life-threatening hemorrhage, yet they have been identified after hospital discharge. There are currently two antivenom (AV) products on the US market to treat rattlesnake envenomations, a Fab product, CroFab® (BTG, UK) and a F (ab')2 product, Anavip® (Bioclon, Mexico). OBJECTIVE: This study intended to characterize the incidence and severity of late coagulopathies reported to a Regional Poison Center (RPC) and hypothesized that late coagulopathies occur at rates higher than previously reported in the literature. Additionally, we sought to compare rates of late coagulopathy between Fab and F (ab')2 AV. METHODS: The investigators performed an in-depth review of all suspected snakebite envenomations from 2018 to 2020 that presented to an Arizona healthcare facility in the RPC's catchment area between January 2018 through December of 2020. Patients were excluded from analysis if they did not receive any antivenom, had an incomplete medical record with the APDIC, were diagnosed as something other than a rattlesnake bite or had a known medical history that clouded the diagnosis or assessment of a rattlesnake envenomation. RESULTS: In total, 522 records were reviewed of which 283 patients met the inclusion criteria. There were 149 patients who received Fab AV and 134 who received F (ab')2. No significant baseline or demographic differences existed between the groups. 95 of the 283 patients developed a late onset coagulopathy. 39% of the late onset coagulopathies were delayed, 32% were recurrent and 29% were persistent. When comparing the two different AV products, delayed or recurrent coagulopathies occurred in 36% of Fab AV- and 10% of F (ab')2 treated patients. Persistent coagulopathies occurred in 17% of Fab AV- and 8% of F (ab')2 treated patients. Interestingly, there were zero cases of late hypofibrinogenemia in any of the 134 F (ab')2 treated patients compared to 26% of all Fab treated ones. The average onset of late coagulopathy post-bite was 8 days for Fab AV and 7 for F (ab')2. CONCLUSION: The results from this study suggest the total rate of late onset coagulopathies may be underestimated. Additionally, our results suggest the potential that F (ab')2 AV may be associated with fewer late onset coagulopathies, especially late onset hypofibrinogenemia.

Arizona Ridge-nosed rattlesnake envenomation: Case report of a personal encounter with the official state reptile of Arizona, Crotalus willardi willardi.

This case report describes the effects of an envenomation from one of the most infrequently encountered species of rattlesnake in the United States, Crotalus willardi willardi (C. w. willardi), the Arizona Ridge-nosed Rattlesnake. A previously healthy 57-year-old male sustained a bite to his non-dominant hand from a C. w. willardi. The most pronounced effect from the envenomation was edema and progression of edema that extended from his hand to the mid bicep. He also experienced erythema and tenderness to palpation in the affected limb, and some diminished range of motion in the hand. He expressed only minimal pain. Other than a mildly positive D-Dimer and leukocytosis, he had no significant hematologic effects and no systemic effects. He was treated with standard doses of Crotalidae Polyvalent Immune Fab (Ovine). He reported complete recovery from the envenomation within three days of the bite. Although envenomation from rattlesnakes is somewhat common in Arizona, knowing the exact species of snake is not. Confirmed documentation is exceedingly rare as most people do not recognize the different rattlesnake species. In addition, some species of rattlesnake (such as C. w. willardi) are especially reclusive and found only in isolated mountainous regions. Being able to confirm an envenomation by C. w. willardi would require not only someone knowledgeable in herpetology, but also, preferably, photographic evidence. This case has both.

Rattling the border wall: Pathophysiological implications of functional and proteomic venom variation between Mexican and US subspecies of the desert rattlesnake Crotalus scutulatus.

While some US populations of the Mohave rattlesnake (Crotalus scutulatus scutulatus) are infamous for being potently neurotoxic, the Mexican subspecies C. s. salvini (Huamantlan rattlesnake) has been largely unstudied beyond crude lethality testing upon mice. In this study we show that at least some populations of this snake are as potently neurotoxic as its northern cousin. Testing of the Mexican antivenom Antivipmyn showed a complete lack of neutralisation for the neurotoxic effects of C. s. salvini venom, while the neurotoxic effects of the US subspecies C. s. scutulatus were time-delayed but ultimately not eliminated. These results document unrecognised potent neurological effects of a Mexican snake and highlight the medical importance of this subspecies, a finding augmented by the ineffectiveness of the Antivipmyn antivenom. These results also influence our understanding of the venom evolution of Crotalus scutulatus, suggesting that neurotoxicity is the ancestral feature of this species, with the US populations which lack neurotoxicity being derived states.

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.