Moccasin Envenomation

Updated: Aug 10, 2016
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Overview

Background

Moccasins are new world pit vipers (family Viperidae, subfamily Crotalinae), which may be identified by a heat-sensing pit anteroinferior to each eye, elliptical pupils, a triangular head, and undivided subcaudal scales. See the image below.

Snake envenomations, moccasins. Copperhead (Agkist Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of Sean Bush, MD.

Moccasins comprise the genus Agkistrodon, which includes the cottonmouth (Agkistrodon piscivorus) and copperhead (Agkistrodon contortrix) in the southeastern United States; the cantil (Agkistrodon bilineatus) in Mexico and Central America; the mamushi (Agkistrodon blomhoffii), Siberian pit viper (Agkistrodon halys), and Central Asian pit viper (Agkistrodon intermedius) in central and northeastern Asia; and the Malayan pit viper (Calloselasma rhodostoma) and hundred-pace snake (Deinagkistrodon acutus) in southeastern Asia. See the image below.

Snake envenomations, moccasins. Cottonmouth or wat Snake envenomations, moccasins. Cottonmouth or water moccasin (Agkistrodon piscivorus). Photo courtesy of Sean Bush, MD.
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Pathophysiology

Envenomation occurs when the moccasin injects venom via hollow movable fangs located in the anterior mouth. The effects of moccasin envenomation are generally similar to rattlesnake envenomation. However, in most cases, moccasin envenomation is less serious than envenomation by rattlesnakes. For further discussion of more severe pit viper envenomation, see Rattlesnake Envenomation.

Moccasin venom is complex, with nearly 50 identified components. These can be broken down into four major categories [1] :

  • Proteolytic enzymes that directly destroy tissue, as happens in digestion of prey animals
  • Inflammatory mediators, including histamine- and bradykinin-like factors, that cause pain, erythema, swelling, and occasionally distributive shock
  • Fibrinolytic enzymes that cleave fibrin into ineffective D-dimers, resulting in coagulopathy
  • Antiplatelet factors that cause thrombocytopenia

Although neurotoxic factors can be detected in moccasin venom, clinically significant neurotoxicity does not occur with envenomation by copperheads or cottonmouths.

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Epidemiology

Frequency

United States

Approximately 5,000 snakebites are reported to poison centers each year. Of the venomous snakebites for which the species is known, moccasins are responsible for 42%. The vast majority of these (86%) are copperhead envenomations. In portions of the southeastern United States, copperheads account for 85% of all reported snake envenomations. [2, 3] See the image below.

Snake envenomations, moccasins. Copperhead (Agkist Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of George Bush.

International

An estimated 300,000-400,000 venomous snakebites occur per year worldwide. The proportion of these caused by Agkistrodon species is not known.

Sex

Incidence of snakebite is higher in males than in females.

Age

Young adults are bitten most commonly. [4]

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Prognosis

The American Association of Poison Control Centers (AAPCC) previously reported only one death from moccasin envenomation since its first annual report in 1983; however, the latest (2014) report includes 1 reported copperhead envenomation death. [5] Prospective studies of morbidity from moccasin envenomation have not been conducted. [6] However, in two retrospective studies of copperhead victims, patients missed a median of 2 or 6 weeks of work.

Nearly all patients fully recover after moccasin envenomation.

Some patients have long-term problems with limb pain and/or swelling, particularly after physical exertion. The proportion of patients that develop these sequelae and the impact of antivenom therapy on this incidence are not known.

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Patient Education

Call professionals, such as animal control, to move snakes.

Never attempt to handle, possess, or kill venomous reptiles.

For patient education resources, see the patient education article Snakebite.

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