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<< Diagnosis And Management Of North American Snake And Scorpion Envenomations

Pathophysiology

Pit Vipers/Crotalids

Crotalid venom is a stunningly complex mixture of proteins that include proteolytic enzymes, collagenases, phospholipases, nucleotidase, hyaluronidase, acetylcholinesterase, and amino acid oxidase. In addition, it contains elemental metals, amino acids, carbohydrates, lipids, serotonin, and even histamine. 18 Local toxic effects include swelling, pain, ecchymosis, and blebs; systemic effects result in coagulopathy, myocardial injury, muscular paralysis, and central nervous system injury. 4,6 See Table 1 for a more detailed description of venom effects.



Crotalid venom has multiple effects on many organ systems and one of the most prominent is the venom's power as an anticoagulant. Recently, it has been the subject of studies looking into clinical applications of a number of proteins isolated from venom for development of new anticoagulant drugs. These proteins have shown to inhibit platelet adhesion by interfering with the binding of vWF to the GPIb receptor and may provide an entirely new target for antiplatelet agents.19

Venom composition will change depending on the species of snake, age, diet, geographic location, and time of the year.4 Several types of Crotalids, once mature, have the ability to vary the amount of venom injected during a strike. Generally, the younger the snake, the more potent their venom.20

Coral Snakes

Coral snake venom is a heterogeneous mixture of peptides and enzymes with primarily neurotoxic effects on nerve conduction and neuromuscular transmission.7 The mechanism of action and pharmacodynamics of coral snake venom is unclear and has apparently not been the subject of any published research. It is unlikely that this uncertainty will be addressed unless, like the Crotalids, a researcher determines a potential clinical use for Elapid venom or one of its components. Some cytotoxic effects may occur but are usually minor especially when compared to Crotalid venom. Often, there are no symptoms for one to five hours but, once they begin, systemic signs and symptoms may progress rapidly. Tremors and cranial nerve dysfunction resulting in ptosis, dysarthria, and dysphagia are common in substantial envenomations. Respiratory depression occurs more rarely and late in the course.

Non-native Venomous Snakes

Imported snakes of the family Elapidae share some of the characteristics of coral snakes, including a tendency for elapid venom to cause mostly neurotoxic effects. Snakes of the family Viperidae, including Central and South American and Asian pit vipers and the true vipers of Africa, the Middle East, and Europe, are similar in effect to the Crotalid pit vipers of North America, with primarily cytotoxic venom, resulting in local tissue damage, coagulopathy, and organ dysfunction.

Scorpions

Scorpion venom is delivered through a tail stinger from two venom glands and is a combination of peptides and proteins with proteolytic and neurotoxic effects. Neurotoxic effects are proposed to be mediated by effects at sodium and potassium channels of neurons.21-22 Most envenomations produce only local effects of pain and swelling. In a randomized, placebo-controlled trial of scorpion antivenom conducted in Tunisia, 82.4% of 825 patients had only local effects. The other 17.6% exhibited systemic effects, primarily autonomic instability, e.g. hypertension, sweating, and fever. Nine (1%) of 825 patients experienced cardiogenic shock, six (0.8%) had pulmonary edema, and two (0.25%) died.23

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Last Modified: 06/27/2017
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