History

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.

Physical Examination

Although moccasin envenomation usually is associated with less severe local effects than rattlesnake envenomation, severe envenomations do occur.^[11]

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.

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.

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.

Complications

Complications of envenomation may include the following:

Coagulopathy (uncommon in moccasin envenomations), thrombocytopenia (uncommon), and bleeding (rare)
Lymphatic injury, leading to prolonged or permanent swelling of the envenomated limb, particularly after exertion
Skin and soft-tissue necrosis
Rhabdomyolysis
Infection (affects ~2% of patients with viperid snake envenomation)
Death (extremely rare)

Also see Complications in Treatment.

Differential Diagnoses

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Media Gallery

Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of Sean Bush, MD.
Snake envenomations, moccasins. Cottonmouth or water moccasin (Agkistrodon piscivorus). Photo courtesy of Sean Bush, MD.
Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of George Bush.
Wound measurement in snakebites. Courtesy of Carolinas Poison Center.
Crotaline treatment algorithm.