Moccasin Envenomation Clinical Presentation

Updated: Aug 10, 2016
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Most bites occur on the extremities. Upper extremity bites predominate in males and are often associated with deliberate handling of the snake. Other findings may include the following:

  • Pain around the bite site
  • Swelling
  • Nausea, vomiting, or diarrhea
  • Syncope, near syncope

Co-intoxication with alcohol is common and may affect the patient's judgment and ability to comply with therapy.



Although moccasin envenomation usually is associated with less severe local effects than rattlesnake envenomation, severe envenomations do occur. [7]

Fang marks are common, but they may be absent.

Hemorrhagic vesicles may be present at the envenomation site.

Tenderness surrounding bite site is almost always present.

Use a pen to mark and time the border of advancing edema and tenderness often enough to gauge progression. Circumferential measurements of the envenomated extremity, repeated over time, may help differentiate swelling that is progressing (getting worse) from swelling that has stabilized (improving or not getting worse) but for which the leading edge is moving proximally because of limb elevation (see image below). Measurements of the contralateral (uninvolved) extremity may be useful for comparison.

Wound measurement in snakebites. Courtesy of Carol Wound measurement in snakebites. Courtesy of Carolinas Poison Center.

Rapidly progressive swelling is usually indicative of a more severe envenomation.

Erythema at the bite site, proximal to the bite site, and along patterns of lymphatic drainage may be noticed.

Ecchymosis and bullae may also be noted.

Bleeding into the tissues of the bite site is common. Systemic bleeding is uncommon in moccasin envenomations, occurring in less than 5% of copperhead envenomations.

Tachycardia is common and due to pain, anxiety, and third-spacing of fluids due to inflammation.

Hypotension is uncommon and usually due to intravascular volume depletion.



A large percentage of bites are considered intentionally interactive—they occur when the snake is handled, kept as a pet, or abused. Many bites are associated with ethanol use.



Complications of envenomation may include the following:

  • Bleeding
  • Compartment syndrome
  • Skin and soft tissue necrosis
  • Infection
  • Death