David L. Hardy

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.

Sympatric rattlesnakes with contrasting mating systems show differences in seasonal patterns of plasma sex steroids

Long-term field studies conducted in Arizona show that two species of sympatric rattlesnakes differ in the structure of their mating systems, primarily in frequency and timing of mating seasons, despite exposure to identical environmental conditions. The western diamond-backed rattlesnake, Crotalus atrox, has two distinct mating seasons within a single annual spermatogenic cycle. The first mating season occurs from late August to early October. Following a hibernation period of 4 months, the second mating season occurs from mid-March to early May. Because there is a mating season in spring, long-term sperm storage by females during winter is facultative. In contrast, the black-tailed rattlesnake, Crotalus molossus, has a single mating season (mid-July to early September) within a single annual spermatogenic cycle. Due to the absence of a mating season in spring, long-term sperm storage by females during winter is obligatory. In both species, ovulation and fertilization occur in spring, and offspring are produced from mid-July to early September. Based on these robust data, we tested the hypotheses that seasonal patterns of plasma sex steroids (testosterone, 5α-dihydrotestosterone, and 17β-estradiol) differ between males in wild populations of C. atrox and C. molossus, and that peak levels would be coincident with the mating seasons. Specifically, we predicted that there would be two peaks of sex steroids in C. atrox and one peak in C. molossus, and that baseline levels would be detected outside the periods of mating and spermatogenesis. Our results supported these predictions. Furthermore, absolute concentrations of plasma testosterone and 5α-dihydrotestosterone, but not 17β-estradiol, were higher in C. atrox than in C. molossus. We discuss a possible scenario for the evolution of the different mating seasons in these sympatric rattlesnakes, and advocate that comparative approaches to address such questions should integrate proximate and ultimate causation to increase explanatory power.

Envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus): report of two cases and the in vitro effects of the venom on fibrinolysis and platelet aggregation

In two cases of human envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus) there was marked swelling and ecchymosis of the bitten extremity and thrombocytopenia and, in one case, hypofibrinogenemia. Treatment consisted of i.v. antivenin, crystalloid solution, fresh frozen plasma and cryoprecipitates, with recovery in each case. In vitro studies showed that the venom had fibrinolytic and platelet aggregating properties; a coagulant effect, although present, was much less marked.

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

Fifteen cases of envenomation by the Mojave rattlesnake (Crotalus scutulatus scutulatus) are reviewed. Systemic effects were observed in eight patients, consisting of early hypotension (3), decreased plasma fibrinogen (3) and platelets (2), elevated fibrinolytic split products (3) and eyelid ptosis (1). Local venom effects were most common and included swelling (15), ecchymosis (10), bleb formation (6) and necrosis (3). Effects upon neuromuscular transmission were neither common nor a clinical problem. Treatment consisted of i.v. crystalloid solution (15) and antivenin (12).

Compartment Syndrome, Fasciotomy, and Neuropathy After a Rattlesnake Envenomation: Aspects of Monitoring and Diagnosis

Abstract Compartment syndrome resulting from pitviper envenomation is uncommon in North America; however, when it does occur, early diagnosis, optimal antivenom therapy, and possible surgical decompression are the primary means of preventing the complication of neuropathy. Here, we report a case of a rattlesnake envenomation in the anterior compartment of the lower leg that required high doses of morphine to control pain. Although compartment syndrome was considered a possible outcome, subfascial pressures were not monitored and antivenom was discontinued at 24 hours. At 36 hours, the patient developed dorsal foot numbness and foot drop, and 15 hours later pressures within the anterior compartment were >68 mm Hg. Emergency fasciotomy was performed 59 hours postenvenomation. Peroneal neuropathy was evident after surgery and only partially recovered postoperatively. Earlier monitoring of subfascial pressures and using those pressures as a guide for decisions about time and dose of CroFab antivenom treatment may have permitted earlier surgical treatment after onset of compartment syndrome or even prevented the onset of this condition.

Fang tip spread, puncture distance, and suction for snake bite

We measured the distance between fang tip punctures in defensive bites by western diamondback rattlesnakes (Crotalus atrox) and the distance between their retracted fangs. Because the fang tips at penetration average 112% further apart than their bases at rest, The Extractor, a device widely marketed in the United States for snake bite first aid, will not simultaneously cover both punctures of most adult New World pitvipers.

Envenomation by the Mexican lance-headed rattlesnake Crotalus polystictus: a case report

A case of envenomation by the Mexican lance-headed rattlesnake, Crotalus polystictus, resulted in local swelling and muscle fasciculation, which abated after i.v. antivenin and an area of necrosis healed. A mild thrombocytopenia and hypofibrinogenemia with elevation of fibrin split products was noted.